000
FXUS62 KCHS 201530
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1030 AM EST TUE JAN 20 2009
.SYNOPSIS...
LOW PRESSURE OFF THE EASTERN NORTH CAROLINA COAST WILL CONTINUE TO
TRACK NORTHEASTWARD AND AWAY FROM THE AREA TODAY. HIGH PRESSURE
WILL THEN BUILD BACK INTO THE AREA TONIGHT THROUGH FRIDAY...BEFORE
THE NEXT COLD FRONT MOVES INTO THE REGION OVER THE UPCOMING
WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
CURRENTLY AT THE SURFACE...AN AREA OF LOW PRESSURE CONTINUES TO
INTENSIFY OFF THE EASTERN NORTH CAROLINA COAST AS IT TRACKS
NORTHEASTWARD AND AWAY FROM THE FORECAST AREA. UPSTREAM A VIGOROUS
SHORTWAVE TROUGH OVER NORTHERN ALABAMA...IS BEGINNING TO ROUND THE
BASE OF A HIGHLY AMPLIFIED EASTERN CONUS UPPER TROUGH. RADAR IMAGERY
SHOWS SCATTERED RETURNS PRIMARILY NORTH OF THE SAVANNAH RIVER. CALLS
RECEIVED FROM THE PUBLIC AS WELL AS REPORTS RELAYED BY LOCAL MEDIA
CONFIRM THAT PRECIPITATION HAS CHANGED OVER TO PRIMARILY SNOW ACROSS
THE AREA. MEANWHILE VISIBLE SATELLITE IMAGERY SHOWS GENERALLY CLOUDY
CONDITIONS OVER A GOOD 2/3RDS OF THE FORECAST AREA WITH PARTLY
CLOUDY TO MOSTLY SUNNY CONDITIONS ALONG THE ALTAMAHA. MAIN NEAR TERM
CONCERN FOR THE REMAINDER OF THE DAY REVOLVES AROUND WINTER WEATHER
AND POTENTIAL SNOW ACCUMULATIONS.
THE AREA OF LOW PRESSURE OFF THE NORTH CAROLINA COAST WILL CONTINUE
TO TRACK NORTHEASTWARD AND AWAY FROM THE FORECAST AREA THIS
AFTERNOON...WHILE A POTENT UPPER LEVEL DISTURBANCE PUSHES INTO THE
REGION. GUIDANCE SHOWS A LAYER OF NEGATIVE SATURATED EQUIVALENT
POTENTIAL VORTICITY UNDERNEATH A LAYER OF FRONTOGENETICAL FORCING
BETWEEN H5 AND H4 HOLDING ON THROUGH MID AFTERNOON PRIMARILY NORTH
OF THE SAVANNAH RIVER AND FOCUSED ACROSS FAR NORTHWESTERN SOUTH
CAROLINA ZONES IN ASSOCIATION WITH LINGERING DEFORMATION ZONE FROM
STORM SYSTEM OFF THE NORTH CAROLINA COAST. ADDITIONALLY...MODELS
SHOW PRETTY DECENT H85-H5 LAYER QG FORCING PUSHING THROUGH THE
REGION IN ASSOCIATION WITH APPROACHING SHORTWAVE TROUGH THIS
AFTERNOON AND INTO EARLY THIS EVENING.
LIMITING MECHANISMS BEHIND ANY ORGANIZED CONVECTIVE BANDING HOWEVER
WILL LIKELY BE DRY AIR IN PLACE IN THE H7 TO H5 LAYER THROUGH MID TO
LATE AFTERNOON AND IN THE H85-H7 LAYER THROUGH ROUGHLY 16/17Z. THIS
ALONG WITH NORTHWESTERLY DOWNSLOPE FLOW AND SMALL SATURATED REGION
IN THE -12 TO -16C DENDRITIC GROWTH RANGE AS SEEN IN MODEL
SOUNDINGS...SHOULD LIMIT ANY POTENTIAL SNOW ACCUMULATIONS TO LESS
THAN AN INCH AND BELOW WARNING CRITERIA.
ONE CAVEAT THAT MAY COME INTO PLAY HOWEVER IS THE ROUGHLY 25 TO 30
NAUTICAL MILE FETCH OVER LAKES MARION AND MOULTRIE WITH A
NORTHWESTERLY LOW LEVEL FLOW LATE THIS AFTERNOON AND THIS EVENING.
COULD SEE SOME ENHANCEMENT GIVEN LINGERING SYNOPTIC FORCING FOR
ASCENT IN ASSOCIATION WITH APPROACHING SHORTWAVE TROUGH...PLENTY OF
SYNOPTIC MOISTURE WITH H85-H7 RH GREATER THAN 60 PERCENT...AND LAKE
SURFACE-H85 DELTA T/S AROUND 20 TO 21C. 1000-850 MB WIND FIELDS WILL
NOT REMAINED LOCKED IN A FIXED DIRECTION FOR A PROLONGED PERIOD OF
TIME HOWEVER TO TAKE ADVANTAGE OF OPTIMUM FETCH. THEREFORE...DON/T
ANTICIPATE ANY ACCUMULATIONS REACHING WARNING CRITERIA OVER A LARGE
ENOUGH AREA TO WARRANT A WINTER STORM WARNING...BUT WOULDN/T BE
SURPRISED TO SEE A FEW ISOLATED REPORTS OF AROUND 2 INCHES DOWNWIND
OF LAKE MOULTRIE.
AS FOR HEADLINES...WILL KEEP ONGOING WINTER WEATHER ADVISORIES IN
TACT BUT EXTEND THEM THROUGH 7 PM THIS EVENING AS SYNOPTIC MOISTURE
AND FORCING ARE EXPECTED TO REMAIN IN PLACE INTO EARLY THIS EVENING.
WILL NEED TO MONITOR CHARLESTON COUNTY CLOSELY FOR A POTENTIAL NEED
FOR A WINTER WEATHER ADVISORY DURING THE EVENING RUSH...BUT AT THIS
TIME IT APPEARS ANY WIDESPREAD ACCUMULATING SNOW...ALBEIT VERY SMALL
AMOUNTS...WILL REMAIN JUST OFF TO THE NORTHWEST.
TEMPERATURES AREN/T EXPECTED TO MOVE MUCH THROUGH THE REMAINDER OF
THE DAY WITH ONGOING STRONG COLD AIR ADVECTION. AFTER EARLY MORNING
HIGHS IN MOST LOCALES...TEMPERATURES SHOULD HOLD IN THE 30S ACROSS
MOST OF THE AREA...WITH SOME LOWER 40S EXPECTED ALONG THE ALTAMAHA
WHERE MORE SUNSHINE WILL BE SEEN.
LAKE WINDS...STRONG PRESSURE RISES /5-6 MB PER 3 HR/ HAVE DEVELOPED
OVER THE PAST COUPLE OF HOURS OVER BERKELEY COUNTY AND SURROUNDING
AREAS. THE TIGHTENED SFC PRES GRADIENT AS A RESULT BETWEEN INCOMING
HIGH PRES AND STRENGTHENING OFFSHORE LOW PRES WILL MAINTAIN STRONG
NW WINDS OVER LAKE MOULTRIE THROUGH THIS AFTN. WILL MAINTAIN THE
LAKE WIND ADVY AS IS...WITH ITS CURRENT EXPIRATION AT 5PM...AND LOOK
FOR WINDS TO STEADILY DIMINISH LATE THIS AFTN.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
CLEARING SKIES AND ONGOING COLD AIR ADVECTION WILL RESULT IN
CHILLY NIGHT ACROSS THE REGION WITH LOWS DROPPING INTO THE UPPER
TEENS WELL INLAND WITH MID 20S CLOSER TO THE COAST. COULD SEE
FLURRIES LINGER ACROSS BERKELEY AND CHARLESTON COUNTY UNTIL SUNSET
BUT NO ADDITIONAL ACCUMULATIONS WILL OCCUR. WIND CHILL VALUES WILL
DROP TO 10-15 INLAND AND CLOSER TO 15-20 ALONG THE COAST...WHICH
IS ABOVE WIND CHILL ADVISORY THRESHOLDS. ANY SNOW OR WET GROUNDS
THAT REMAIN AFTER SUNSET WILL QUICKLY REFREEZE AND THERE IS A
POSSIBILITY THAT BLACK ICE COULD BECOME AN ISSUE IN PLACES. THIS
WILL BE CAREFULLY MONITORED AS A WINTER WEATHER ADVISORY FOR BLACK
ICE MAY BE NEEDED.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST ON
WEDNESDAY...AS THE AXIS OF THE DEEP UPPER TROUGH SHIFTS INTO THE
ATLANTIC. THIS PATTERN WILL ALLOW FOR RAIN FREE WEATHER AND A
WARMING TREND THROUGH LATE WEEK. HIGH TEMPERATURES WILL RETURN TO
NEAR SEASONAL NORMALS BY THURSDAY...REACHING THE UPPER 50S ACROSS
THE FORECAST AREA.
THE CENTER OF HIGH PRESSURE WILL GRADUALLY SLIP TO THE SOUTHEAST
BY FRIDAY...WHILE A COLD FRONT APPROACHES FROM THE WEST. THE REGION
WILL FALL WITHIN WARM SOUTHERLY FLOW AHEAD OF THE FRONT...AND EXPECT
HIGH TEMPERATURES TO REACH THE LOWER TO MID 60S WITHIN THE WARM
SECTOR FRIDAY.
THERE ARE SOME TIMING DIFFERENCES BETWEEN THE ECMWF AND GFS
REGARDING COLD FRONTAL PASSAGE OVER THE WEEKEND...WITH GFS BEING
THE FASTER OF THE TWO SOLUTIONS. AS A COMPROMISE BETWEEN THE
MODELS...HAVE INTRODUCED A SLIGHT CHANCE FOR SHOWERS AFTER
MIDNIGHT EARLY SATURDAY MORNING....WITH HIGHEST RAIN CHANCES LATER
ON SATURDAY. WILL CAP POPS AT 30 PERCENT...AS MODELS WILL LIKELY
ADJUST TIMING IN SUBSEQUENT RUNS.
DECREASE RAIN CHANCES FROM WEST TO EAST AS THE FRONT DROPS TO THE
SOUTHEAST OFFSHORE ON SUNDAY. GFS RAPIDLY BUILDS HIGH PRESSURE
DOWN FROM THE NORTH BEHIND THE FRONT ON SUNDAY...SETTING UP A
STRONG INLAND WEDGE/COASTAL TROUGH PATTERN. A QUICK GLANCE AT 00Z
ECMWF APPEARS TO SUGGEST IT ALSO COMING AROUND TO A SIMILAR
PATTERN. HAVE THUS REINTRODUCED SLIGHT CHANCE POPS ACROSS THE AREA
LATE SUNDAY NIGHT INTO MONDAY. COOLER HIGH TEMPERATURES IN THE 50S
ARE POSSIBLE WITHIN ANY INLAND WEDGE ON SUNDAY.
&&
.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
KCHS...ANY PRECIP THAT FALLS IS EXPECTED TO BE IN THE FORM OF SNOW.
WILL MAINTAIN MENTION OF 4SM -SHSN BETWEEN 15-18Z AS ACTIVITY
UPSTREAM CONTINUES TO DEVELOP. MVFR CEILINGS WILL PERSIST ALONG
WITH GUSTY WINDS THROUGH MUCH OF THE AFTERNOON BEFORE VFR
CONDITIONS RETURN BY 00Z AS CLOUD COVER GETS SCOURED OUT BEHIND
DEPARTING LOW PRESSURE.
KSAV...SATELLITE OBSERVATIONS CONTINUE TO INDICATE LOW CLOUDS ON
THE VERGE OF OVERSPREADING THE KSAV TERMINAL. EXPECT MVFR CEILINGS
TO OCCUR BY 18Z OVER THE TERMINAL AND PERSIST THIS AFTERNOON ALONG
WITH GUSTY WINDS. CEILINGS SHOULD RECOVER TO VFR BY THE EVENING AS
CLOUD COVER BEGINS TO SCOUR OUT BEHIND DEPARTING LOW PRESSURE. NO
PRECIPITATION IS EXPECTED AT THE KSAV TERMINAL OUTSIDE OF A FEW
FLURRIES THIS MORNING...BUT CERTAINLY NOT ENOUGH TO INCLUDE A
MENTION ON THE 12Z TAF.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
FRIDAY NIGHT. COULD SEE MVFR CONDITIONS RETURN SATURDAY AS A COLD
FRONT PUSHES INTO THE AREA.
&&
.MARINE...
HAVE OBSERVED CONTINUED STRONG PRES RISES OVER THE SC/GA COASTAL
REGION THE PAST FEW HOURS AND THIS HAS BEEN REFLECTED IN SEEING GALE
TO NEAR GALE FORCE WINDS AT BOTH BUOYS 41004 AND 41008. THE STRONGER
WINDS WERE EARLIER THIS MORNING SEEN ALONG AND S OF THE ALTAMAHA
RIVER BUT THAT HAS NOW TRANSITIONED TO WRN PORTIONS OF THE CWFA AS
THE OFFSHORE LOW STRENGTHENS AND HIGH PRES TRIES TO COME IN. LATEST
MRP AND MMG GUIDANCE INDICATES SOLID SUSTAINED SCA WINDS BUT OVER
THE WARMER WATERS NEAR THE GULF STREAM...AM CONCERNED THAT FREQUENT
GUSTS TO GALE FORCE CAN BE MAINTAINED THROUGH THE DAY. THUS...HAVE
OPTED TO EXTEND THE GALE WARNING FOR THE OFFSHORE GA WATERS THROUGH
THIS AFTN...AND WILL LOOK FOR WINDS TO SUBSIDE BELOW GALE FORCE BY
LATE THIS AFTN. WILL ALSO KEEP SOLID SCA CONDITIONS GOING FOR ALL
THE NEARSHORE WATERS...INCLUDING CHAS HARBOR. BY TONIGHT...WINDS
WILL WILL DIMINISH AS HIGH PRESSURE TRIES TO BUILD IN FROM THE WEST.
ONLY THE GA OFFSHORE WATERS LOOK TO REMAIN WITHIN SCA THRESHOLDS.
WEDNESDAY THROUGH SUNDAY...HIGH PRESSURE WILL BUILD BACK INTO THE
REGION WEDNESDAY THROUGH FRIDAY...WITH THE NEXT COLD FRONT EXPECTED
TO APPROACH FROM THE WEST FRIDAY NIGHT AND PUSH THROUGH THE MARINE
AREA LATE SATURDAY. STRONG WEST WINDS EARLY WEDNESDAY WILL GRADUALLY
DIMINISH WITHIN BUILDING HIGH PRESSURE...THEN BECOME SOUTHWEST AHEAD
OF THE FRONT BY EARLY FRIDAY. GFS MODEL DEVELOPS A TIGHT PRESSURE
GRADIENT AS THE FRONT DROPS SOUTH THROUGH THE AREA LATE
SATURDAY...SUGGESTING WINDS AND SEAS COULD REACH SMALL CRAFT
ADVISORY CRITERIA.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR SCZ045.
WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR
SCZ043>045.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ330-
350-352-354.
GALE WARNING UNTIL 5 PM EST THIS AFTERNOON FOR AMZ374.
&&
$$
JRJ/JPC/DPB
000
FXUS62 KCHS 201156
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
656 AM EST TUE JAN 20 2009
.SYNOPSIS...
LOW PRESSURE ALONG THE SOUTH CAROLINA COAST WILL SHIFT NORTHEAST
OF THE AREA TODAY. HIGH PRESSURE WILL THEN BUILD BACK INTO THE
AREA TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT
MOVES INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
UPDATE...STARTING TO GET REPORTS OF LIGHT SNOW AROUND ORANGEBURG.
TEMPERATURES HAVE FALLEN TO NEAR FREEZING AT WALTERBORO AND WILL
CONTINUE TO TUMBLE ACROSS COASTAL SOUTH CAROLINA THROUGH SUNRISE.
THE 10Z RUC IS FORECASTING A INCH OF SNOW FROM HARLEYVILLE UP TO
SAINT STEPHEN WITH A 1/2 INCH FROM WILLIAMS DOWN TO WALTERBORO
THEN EAST TO JEDBURG AND JAMESTOWN...WHICH SEEMS REASONABLE GIVEN
CURRENT RADAR AND SATELLITE TRENDS. STILL DO NOT HAVE ENOUGH
CONFIDENCE THAT MEASURABLE SNOWFALL WILL REACH IN TO CHARLESTON
COUNTY...SO THE CURRENT CONFIGURATION OF THE WINTER WEATHER
ADVISORY LOOKS ON TRACK. WILL CONTINUE TO MONITOR.
VERY DIFFICULT WINTER WEATHER FORECAST FOR THE FORECAST AREA
TODAY. A POTENT SHORTWAVE EVIDENT ON WATER VAPOR IMAGERY ACROSS
SOUTHERN MISSOURI WILL ROUND THE BASE OF THE AMPLIFYING LONG-WAVE
TROUGH TODAY. SURFACE OBSERVATIONS INDICATE CYCLOGENESIS IS WELL
UNDERWAY WITH THE CENTER OF THE LOW POSITIONED SOMEWHERE ACROSS
BERKELEY OR WILLIAMSBURG COUNTIES. SATELLITE TRENDS SUGGEST THE
SYSTEM IS BEGINNING TO RAPIDLY MATURE WITH WHAT APPEARS TO BE A
BAROCLINIC LEAF FORMING ALONG THE NORTH CAROLINA COAST. THE
SURFACE CYCLONE WILL STEADILY INTENSIFY THROUGH THE DAY AS UPPER
DIFLUENCE AHEAD OF THE APPROACHING SHORTWAVE INCREASES. COLD
CYCLONIC FLOW ON THE BACKSIDE OF THE DEPARTING LOW WILL HELP DRAG
COLD AND SOMEWHAT DRIER IN FROM THE NORTH THIS MORNING WITH WRAP
AROUND PRECIPITATION IMPACTING MAINLY THE NORTHERN HALF OF THE
FORECAST AREA. ALL OF OUR AVAILABLE SHORT TERM GUIDANCE SUGGESTS
RAIN WILL QUICKLY CHANGE TO SNOW AROUND SUNRISE AS SURFACE
TEMPERATURES RAPIDLY DROP WITH THERMAL PROFILES SUPPORTING SNOW
THROUGH THE AFTERNOON HOURS. THIS QUESTION NOW IS HOW MUCH
MEASURABLE SNOW WILL FALL.
IMPRESSIVE QUASIGEOSTROPHIC FORCING AHEAD OF THE APPROACHING
SHORTWAVE IS ALREADY SUPPORTING A FAIRLY LARGE SWATH OF LIGHT
RAIN AND SNOW STRETCHING FROM THE MIDLANDS THROUGH EASTERN NORTH
CAROLINA. MODELS SUGGEST THE STRONGEST FORCING AND HEAVIEST SNOW
WILL REMAIN TO THE NORTH WITH ONLY THE FAR NORTHERN COUNTIES
GETTING INTO THE FRINGES OF THE STRONGEST 850-700MB FRONTOGENETIC
ZONE. HOWEVER THE NAM/GFS/SREF AND 4-KM NSSL WRF ALL ROTATE A
FAIRLY HEALTHY AREA OF LIGHT SNOW INTO PORTIONS OF COLLETON-
DORCHESTER-BERKELEY AND CHARLESTON COUNTY LATER THIS MORNING.
GIVEN THE REFLECTIVITY TRENDS NOTED ON THE KCAE AND KGSP RADARS WE
HAVE NO REASON TO DISPUTE THIS...BUT THIS WILL BE A VERY CLOSE
CALL AS THE PRECIPITATION COULD VERY WELL PASS JUST TO THE NORTH
OF THESE COUNTIES. ATTM THE BEST CHANCES FOR MEASURABLE SNOW LOOKS
TO REMAIN ROUGHLY NORTH OF A LINE FROM ISLANDTON TO WALTERBORO-
SUMMERVILLE-HUGER AND SHULERVILLE WITH ONLY TRACE AMOUNTS OR
FLURRIES FARTHER TO THE SOUTH. TOTAL ACCUMULATIONS LOOK TO BE NO
HIGHER THAN 1/2 TO 1 INCH AT BEST IN THESE AREAS AND MAINLY
CONFINED TO GRASSY SURFACES. THE SNOW LOOKS TO BECOME SOMEWHAT
CONVECTIVE BY MID-LATE MORNING AS MID-LEVEL LAPSE RATES STEEPEN SO
ISOLATED HIGHER AMOUNTS CAN NOT BE RULED OUT WHERE BURSTS OF
HEAVIER SNOW OCCUR. ITS INTERESTING TO NOTE THAT OUR LOCAL
WORKSTATION WRF MODEL DEVELOPS WHAT APPEARS TO BE A SMALL AREA OF
LAKE ENHANCED SNOWS DOWNWIND OF LAKES MOULTRIE AND MARION BY LATE
MORNING AS THERMAL PROFILES STEEPEN AND LOW-LEVEL TRAJECTORIES
TURN NORTHWEST. TOUGH CALL ON WHETHER THIS BANDED FEATURE WILL
FORM BUT ITS WORTH NOTING AS A SMALL AREA OF ENHANCED CONVECTIVE
SNOWS COULD CERTAINLY MATERIALIZE.
AFTER MUCH INTERNAL DISCUSSION AND COORDINATION WITH WFO/S ILM
AND CAE...WE PLAN TO CANCEL THE WINTER WEATHER ADVISORY FOR
JENKINS-SCREVEN-ALLENDALE AND HAMPTON COUNTIES AND MAINTAIN THE
ADVISORY UNTIL 5 PM THIS AFTERNOON FOR INLAND COLLETON-DORCHESTER
AND BERKELEY. CHARLESTON COUNTY IS STILL A TOSS UP...PARTICULARLY
FOR THE NORTH CHARLESTON AREA...BUT THERE IS JUST NOT ENOUGH
EVIDENCE IN THE AVAILABLE GUIDANCE TO SUPPORT AN EXPANSION INTO
THE CHARLESTON METRO AREA JUST YET. THIS COULD CERTAINLY CHANGE
LATER THIS MORNING AS MESOSCALE TRENDS BECOME MORE EVIDENT.
WILL GO WITH POPS AROUND 50 PERCENT ACROSS THE ADVISORY AREA
TAPERING TO 20 PERCENT ALONG THE SAVANNAH RIVER WITH POPS
DIMINISHING FROM SW-NE AS THE AFTERNOON PROGRESSES. ANY LINGERING
SNOW SHOWERS SHOULD DIMINISH TO FLURRIES ACROSS THE CHARLESTON
TRI-COUNTY AREA BY MID AFTERNOON.
HIGHS WILL BE EXTREMELY TRICKY TODAY AND WILL BE HIGHLY DEPENDANT
ON PRECIPITATION COVERAGE. WITH EVAPORATIONAL COOLING LIKELY TO
DOMINATE ACROSS THE NORTH WITH THE SNOW...THE COLDEST TEMPERATURES
WILL FOUND THERE WHILE FARTHER SOUTH SOME MORNING SUN MAY PRODUCE
A QUICK RISE IN TEMPERATURES SOUTH OF SAVANNAH. IN ADDITION SOME
AREAS ACROSS THE NORTH COULD SEE TEMPERATURES HOLD STEADY OR DROP
AFTER SUNRISE AS EVAPORATIONAL PROCESSES TAKE HOLD. WILL SHOW
HIGHS MID-UPPER 30S NORTH WITH UPPER 40S ACROSS THE FAR SOUTH BUT
FURTHER ADJUSTMENTS WILL LIKELY BE NEEDED LATER THIS MORNING.
LAKE WINDS...WINDS ARE EXPECTED TO INCREASE TO LAKE WIND ADVISORY
THRESHOLDS LATER THIS MORNING AS THE GRADIENT TIGHTENS ON THE
BACKSIDE OF DEPARTING LOW PRESSURE.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
CLEARING SKIES AND ONGOING COLD AIR ADVECTION WILL RESULT IN
CHILLY NIGHT ACROSS THE REGION WITH LOWS DROPPING INTO THE UPPER
TEENS WELL INLAND WITH MID 20S CLOSER TO THE COAST. COULD SEE
FLURRIES LINGER ACROSS BERKELEY AND CHARLESTON COUNTY UNTIL SUNSET
BUT NO ADDITIONAL ACCUMULATIONS WILL OCCUR. WIND CHILL VALUES WILL
DROP TO 10-15 INLAND AND CLOSER TO 15-20 ALONG THE COAST...WHICH
IS ABOVE WIND CHILL ADVISORY THRESHOLDS. ANY SNOW OR WET GROUNDS
THAT REMAIN AFTER SUNSET WILL QUICKLY REFREEZE AND THERE IS A
POSSIBILITY THAT BLACK ICE COULD BECOME AN ISSUE IN PLACES. THIS
WILL BE CAREFULLY MONITORED AS A WINTER WEATHER ADVISORY FOR BLACK
ICE MAY BE NEEDED.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST ON
WEDNESDAY...AS THE AXIS OF THE DEEP UPPER TROUGH SHIFTS INTO THE
ATLANTIC. THIS PATTERN WILL ALLOW FOR RAIN FREE WEATHER AND A
WARMING TREND THROUGH LATE WEEK. HIGH TEMPERATURES WILL RETURN TO
NEAR SEASONAL NORMALS BY THURSDAY...REACHING THE UPPER 50S ACROSS
THE FORECAST AREA.
THE CENTER OF HIGH PRESSURE WILL GRADUALLY SLIP TO THE SOUTHEAST
BY FRIDAY...WHILE A COLD FRONT APPROACHES FROM THE WEST. THE REGION
WILL FALL WITHIN WARM SOUTHERLY FLOW AHEAD OF THE FRONT...AND EXPECT
HIGH TEMPERATURES TO REACH THE LOWER TO MID 60S WITHIN THE WARM
SECTOR FRIDAY.
THERE ARE SOME TIMING DIFFERENCES BETWEEN THE ECMWF AND GFS
REGARDING COLD FRONTAL PASSAGE OVER THE WEEKEND...WITH GFS BEING
THE FASTER OF THE TWO SOLUTIONS. AS A COMPROMISE BETWEEN THE
MODELS...HAVE INTRODUCED A SLIGHT CHANCE FOR SHOWERS AFTER
MIDNIGHT EARLY SATURDAY MORNING....WITH HIGHEST RAIN CHANCES LATER
ON SATURDAY. WILL CAP POPS AT 30 PERCENT...AS MODELS WILL LIKELY
ADJUST TIMING IN SUBSEQUENT RUNS.
DECREASE RAIN CHANCES FROM WEST TO EAST AS THE FRONT DROPS TO THE
SOUTHEAST OFFSHORE ON SUNDAY. GFS RAPIDLY BUILDS HIGH PRESSURE
DOWN FROM THE NORTH BEHIND THE FRONT ON SUNDAY...SETTING UP A
STRONG INLAND WEDGE/COASTAL TROUGH PATTERN. A QUICK GLANCE AT 00Z
ECMWF APPEARS TO SUGGEST IT ALSO COMING AROUND TO A SIMILAR
PATTERN. HAVE THUS REINTRODUCED SLIGHT CHANCE POPS ACROSS THE AREA
LATE SUNDAY NIGHT INTO MONDAY. COOLER HIGH TEMPERATURES IN THE 50S
ARE POSSIBLE WITHIN ANY INLAND WEDGE ON SUNDAY.
&&
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
KCHS...CEILINGS HAVE LOWERED TO MVFR DURING THE PAST HOUR AND
SHOULD SETTLE TOWARDS LOW-END IFR THROUGH SUNRISE. LIGHT RAIN AND
SNOW CONTINUES TO BLOSSOM OVER THE SOUTH CAROLINA MIDLANDS AND
SOME OF THIS ACTIVITY MAY BRUSH THE KCHS TERMINAL AFTER SUNRISE.
WILL MAINTAIN A MENTION OF 4SM -SHSN BETWEEN 14-18Z. MVFR CEILINGS
WILL PERSIST ALONG WITH GUSTY WINDS THROUGH MUCH OF THE AFTERNOON
BEFORE VFR CONDITIONS RETURN BY 00Z AS CLOUD COVER GETS SCOURED
OUT BEHIND DEPARTING LOW PRESSURE.
KSAV...SATELLITE AND UPSTREAM OBSERVATIONS INDICATE LOW CLOUDS ARE
ON THE VERGE OF OVERSPREADING THE KSAV TERMINAL. EXPECT MVFR
CEILINGS TO OCCUR THERE SHORTLY AND PERSIST FOR MUCH OF THE DAY
ALONG WITH GUSTY WINDS. CEILINGS SHOULD RECOVER TO VFR BY MID
AFTERNOON AS CLOUD COVER BEGINS TO SCOUR OUT BEHIND DEPARTING LOW
PRESSURE. NO PRECIPITATION IS EXPECTED AT THE KSAV TERMINAL
OUTSIDE OF A FEW FLURRIES THIS MORNING...BUT CERTAINLY NOT ENOUGH
TO INCLUDE A MENTION ON THE 12Z TAF.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
FRIDAY NIGHT. COULD SEE MVFR CONDITIONS RETURN SATURDAY AS A COLD
FRONT PUSHES INTO THE AREA.
&&
.MARINE...
LARGE PRESSURE RISES ON THE BACKSIDE OF THE DEVELOPING SURFACE LOW
IS SUPPORTING GALE FORCE WINDS ACROSS MUCH OF NORTHEAST FLORIDA
AND SOUTHEAST GEORGIA OFFSHORE WATERS THIS MORNING. 41012 HAS
REPORTED WINDS IN EXCESS OF 40 KT OVER THE PAST FEW HOURS AND
41008 IS BEGINNING TO GUST TO GALE FORCE. HAVE RAISED A GALE
WARNING FOR OUR GEORGIA OFFSHORE LEG UNTIL 11 AM. THE GEORGIA
NEARSHORE WATERS ARE A TOUGH CALL BUT SUSPECT A STRONG SMALL CRAFT
ADVISORY WILL WORK THERE. FARTHER NORTH...WINDS WILL QUICKLY
INCREASE THIS MORNING AS THE LOW MOVES NORTHEAST OF THE REGION.
WILL MAINTAIN SMALL CRAFT ADVISORIES FOR THE SOUTH CAROLINA
NEARSHORE WATERS AND THE CHARLESTON HARBOR THROUGH LATE AFTERNOON.
BY TONIGHT...WINDS WILL WILL DIMINISH AS HIGH PRESSURE TRIES TO
BUILD IN FROM THE WEST. ONLY THE GEORGIA OFFSHORE WATERS LOOK TO
REMAIN WITHIN SMALL CRAFT ADVISORY THRESHOLDS.
WEDNESDAY THROUGH SUNDAY...HIGH PRESSURE WILL BUILD BACK INTO THE
REGION WEDNESDAY THROUGH FRIDAY...WITH THE NEXT COLD FRONT
EXPECTED TO APPROACH FROM THE WEST FRIDAY NIGHT AND PUSH THROUGH
THE MARINE AREA LATE SATURDAY. STRONG WEST WINDS EARLY WEDNESDAY
WILL GRADUALLY DIMINISH WITHIN BUILDING HIGH PRESSURE...THEN
BECOME SOUTHWEST AHEAD OF THE FRONT BY EARLY FRIDAY. GFS MODEL
DEVELOPS A TIGHT PRESSURE GRADIENT AS THE FRONT DROPS SOUTH
THROUGH THE AREA LATE SATURDAY...SUGGESTING WINDS AND SEAS COULD
REACH SMALL CRAFT ADVISORY CRITERIA.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR SCZ045.
WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
SCZ043>045.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ330-
350-352-354.
GALE WARNING UNTIL 11 AM EST THIS MORNING FOR AMZ374.
&&
$$
ST
000
FXUS62 KCHS 201117
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
617 AM EST TUE JAN 20 2009
.SYNOPSIS...
LOW PRESSURE ALONG THE SOUTH CAROLINA COAST WILL SHIFT NORTHEAST
OF THE AREA TODAY. HIGH PRESSURE WILL THEN BUILD BACK INTO THE
AREA TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT
MOVES INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
VERY DIFFICULT WINTER WEATHER FORECAST FOR THE FORECAST AREA TODAY.
A POTENT SHORTWAVE EVIDENT ON WATER VAPOR IMAGERY ACROSS SOUTHERN
MISSOURI WILL ROUND THE BASE OF THE AMPLIFYING LONG-WAVE TROUGH
TODAY. SURFACE OBSERVATIONS INDICATE CYCLOGENESIS IS WELL
UNDERWAY WITH THE CENTER OF THE LOW POSITIONED SOMEWHERE ACROSS
BERKELEY OR WILLIAMSBURG COUNTIES. SATELLITE TRENDS SUGGEST THE
SYSTEM IS BEGINNING TO RAPIDLY MATURE WITH WHAT APPEARS TO BE A
BAROCLINIC LEAF FORMING ALONG THE NORTH CAROLINA COAST. THE
SURFACE CYCLONE WILL STEADILY INTENSIFY THROUGH THE DAY AS UPPER
DIFLUENCE AHEAD OF THE APPROACHING SHORTWAVE INCREASES. COLD
CYCLONIC FLOW ON THE BACKSIDE OF THE DEPARTING LOW WILL HELP DRAG
COLD AND SOMEWHAT DRIER IN FROM THE NORTH THIS MORNING WITH WRAP
AROUND PRECIPITATION IMPACTING MAINLY THE NORTHERN HALF OF THE
FORECAST AREA. ALL OF OUR AVAILABLE SHORT TERM GUIDANCE SUGGESTS
RAIN WILL QUICKLY CHANGE TO SNOW AROUND SUNRISE AS SURFACE
TEMPERATURES RAPIDLY DROP WITH THERMAL PROFILES SUPPORTING SNOW
THROUGH THE AFTERNOON HOURS. THIS QUESTION NOW IS HOW MUCH
MEASURABLE SNOW WILL FALL.
IMPRESSIVE QUASIGEOSTROPHIC FORCING AHEAD OF THE APPROACHING
SHORTWAVE IS ALREADY SUPPORTING A FAIRLY LARGE SWATH OF LIGHT
RAIN AND SNOW STRETCHING FROM THE MIDLANDS THROUGH EASTERN NORTH
CAROLINA. MODELS SUGGEST THE STRONGEST FORCING AND HEAVIEST SNOW
WILL REMAIN TO THE NORTH WITH ONLY THE FAR NORTHERN COUNTIES
GETTING INTO THE FRINGES OF THE STRONGEST 850-700MB FRONTOGENETIC
ZONE. HOWEVER THE NAM/GFS/SREF AND 4-KM NSSL WRF ALL ROTATE A
FAIRLY HEALTHY AREA OF LIGHT SNOW INTO PORTIONS OF COLLETON-
DORCHESTER-BERKELEY AND CHARLESTON COUNTY LATER THIS MORNING.
GIVEN THE REFLECTIVITY TRENDS NOTED ON THE KCAE AND KGSP RADARS WE
HAVE NO REASON TO DISPUTE THIS...BUT THIS WILL BE A VERY CLOSE
CALL AS THE PRECIPITATION COULD VERY WELL PASS JUST TO THE NORTH
OF THESE COUNTIES. ATTM THE BEST CHANCES FOR MEASURABLE SNOW LOOKS
TO REMAIN ROUGHLY NORTH OF A LINE FROM ISLANDTON TO WALTERBORO-
SUMMERVILLE-HUGER AND SHULERVILLE WITH ONLY TRACE AMOUNTS OR
FLURRIES FARTHER TO THE SOUTH. TOTAL ACCUMULATIONS LOOK TO BE NO
HIGHER THAN 1/2 TO 1 INCH AT BEST IN THESE AREAS AND MAINLY
CONFINED TO GRASSY SURFACES. THE SNOW LOOKS TO BECOME SOMEWHAT
CONVECTIVE BY MID-LATE MORNING AS MID-LEVEL LAPSE RATES STEEPEN SO
ISOLATED HIGHER AMOUNTS CAN NOT BE RULED OUT WHERE BURSTS OF
HEAVIER SNOW OCCUR. ITS INTERESTING TO NOTE THAT OUR LOCAL
WORKSTATION WRF MODEL DEVELOPS WHAT APPEARS TO BE A SMALL AREA OF
LAKE ENHANCED SNOWS DOWNWIND OF LAKES MOULTRIE AND MARION BY LATE
MORNING AS THERMAL PROFILES STEEPEN AND LOW-LEVEL TRAJECTORIES
TURN NORTHWEST. TOUGH CALL ON WHETHER THIS BANDED FEATURE WILL
FORM BUT ITS WORTH NOTING AS A SMALL AREA OF ENHANCED CONVECTIVE
SNOWS COULD CERTAINLY MATERIALIZE.
AFTER MUCH INTERNAL DISCUSSION AND COORDINATION WITH WFO/S ILM
AND CAE...WE PLAN TO CANCEL THE WINTER WEATHER ADVISORY FOR
JENKINS-SCREVEN-ALLENDALE AND HAMPTON COUNTIES AND MAINTAIN THE
ADVISORY UNTIL 5 PM THIS AFTERNOON FOR INLAND COLLETON-DORCHESTER
AND BERKELEY. CHARLESTON COUNTY IS STILL A TOSS UP...PARTICULARLY
FOR THE NORTH CHARLESTON AREA...BUT THERE IS JUST NOT ENOUGH
EVIDENCE IN THE AVAILABLE GUIDANCE TO SUPPORT AN EXPANSION INTO
THE CHARLESTON METRO AREA JUST YET. THIS COULD CERTAINLY CHANGE
LATER THIS MORNING AS MESOSCALE TRENDS BECOME MORE EVIDENT.
WILL GO WITH POPS AROUND 50 PERCENT ACROSS THE ADVISORY AREA
TAPERING TO 20 PERCENT ALONG THE SAVANNAH RIVER WITH POPS
DIMINISHING FROM SW-NE AS THE AFTERNOON PROGRESSES. ANY LINGERING
SNOW SHOWERS SHOULD DIMINISH TO FLURRIES ACROSS THE CHARLESTON
TRI-COUNTY AREA BY MID AFTERNOON.
HIGHS WILL BE EXTREMELY TRICKY TODAY AND WILL BE HIGHLY DEPENDANT
ON PRECIPITATION COVERAGE. WITH EVAPORATIONAL COOLING LIKELY TO
DOMINATE ACROSS THE NORTH WITH THE SNOW...THE COLDEST TEMPERATURES
WILL FOUND THERE WHILE FARTHER SOUTH SOME MORNING SUN MAY PRODUCE
A QUICK RISE IN TEMPERATURES SOUTH OF SAVANNAH. IN ADDITION SOME
AREAS ACROSS THE NORTH COULD SEE TEMPERATURES HOLD STEADY OR DROP
AFTER SUNRISE AS EVAPORATIONAL PROCESSES TAKE HOLD. WILL SHOW
HIGHS MID-UPPER 30S NORTH WITH UPPER 40S ACROSS THE FAR SOUTH BUT
FURTHER ADJUSTMENTS WILL LIKELY BE NEEDED LATER THIS MORNING.
LAKE WINDS...WINDS ARE EXPECTED TO INCREASE TO LAKE WIND ADVISORY
THRESHOLDS LATER THIS MORNING AS THE GRADIENT TIGHTENS ON THE
BACKSIDE OF DEPARTING LOW PRESSURE.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
CLEARING SKIES AND ONGOING COLD AIR ADVECTION WILL RESULT IN
CHILLY NIGHT ACROSS THE REGION WITH LOWS DROPPING INTO THE UPPER
TEENS WELL INLAND WITH MID 20S CLOSER TO THE COAST. COULD SEE
FLURRIES LINGER ACROSS BERKELEY AND CHARLESTON COUNTY UNTIL SUNSET
BUT NO ADDITIONAL ACCUMULATIONS WILL OCCUR. WIND CHILL VALUES WILL
DROP TO 10-15 INLAND AND CLOSER TO 15-20 ALONG THE COAST...WHICH
IS ABOVE WIND CHILL ADVISORY THRESHOLDS. ANY SNOW OR WET GROUNDS
THAT REMAIN AFTER SUNSET WILL QUICKLY REFREEZE AND THERE IS A
POSSIBILITY THAT BLACK ICE COULD BECOME AN ISSUE IN PLACES. THIS
WILL BE CAREFULLY MONITORED AS A WINTER WEATHER ADVISORY FOR BLACK
ICE MAY BE NEEDED.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST ON
WEDNESDAY...AS THE AXIS OF THE DEEP UPPER TROUGH SHIFTS INTO THE
ATLANTIC. THIS PATTERN WILL ALLOW FOR RAIN FREE WEATHER AND A
WARMING TREND THROUGH LATE WEEK. HIGH TEMPERATURES WILL RETURN TO
NEAR SEASONAL NORMALS BY THURSDAY...REACHING THE UPPER 50S ACROSS
THE FORECAST AREA.
THE CENTER OF HIGH PRESSURE WILL GRADUALLY SLIP TO THE SOUTHEAST
BY FRIDAY...WHILE A COLD FRONT APPROACHES FROM THE WEST. THE REGION
WILL FALL WITHIN WARM SOUTHERLY FLOW AHEAD OF THE FRONT...AND EXPECT
HIGH TEMPERATURES TO REACH THE LOWER TO MID 60S WITHIN THE WARM
SECTOR FRIDAY.
THERE ARE SOME TIMING DIFFERENCES BETWEEN THE ECMWF AND GFS
REGARDING COLD FRONTAL PASSAGE OVER THE WEEKEND...WITH GFS BEING
THE FASTER OF THE TWO SOLUTIONS. AS A COMPROMISE BETWEEN THE
MODELS...HAVE INTRODUCED A SLIGHT CHANCE FOR SHOWERS AFTER
MIDNIGHT EARLY SATURDAY MORNING....WITH HIGHEST RAIN CHANCES LATER
ON SATURDAY. WILL CAP POPS AT 30 PERCENT...AS MODELS WILL LIKELY
ADJUST TIMING IN SUBSEQUENT RUNS.
DECREASE RAIN CHANCES FROM WEST TO EAST AS THE FRONT DROPS TO THE
SOUTHEAST OFFSHORE ON SUNDAY. GFS RAPIDLY BUILDS HIGH PRESSURE
DOWN FROM THE NORTH BEHIND THE FRONT ON SUNDAY...SETTING UP A
STRONG INLAND WEDGE/COASTAL TROUGH PATTERN. A QUICK GLANCE AT 00Z
ECMWF APPEARS TO SUGGEST IT ALSO COMING AROUND TO A SIMILAR
PATTERN. HAVE THUS REINTRODUCED SLIGHT CHANCE POPS ACROSS THE AREA
LATE SUNDAY NIGHT INTO MONDAY. COOLER HIGH TEMPERATURES IN THE 50S
ARE POSSIBLE WITHIN ANY INLAND WEDGE ON SUNDAY.
&&
.AVIATION /11Z TUESDAY THROUGH SATURDAY/...
KCHS...CEILINGS HAVE LOWERED TO MVFR DURING THE PAST HOUR AND
SHOULD SETTLE TOWARDS LOW-END IFR THROUGH SUNRISE. LIGHT RAIN AND
SNOW CONTINUES TO BLOSSOM OVER THE SOUTH CAROLINA MIDLANDS AND
SOME OF THIS ACTIVITY MAY BRUSH THE KCHS TERMINAL AFTER SUNRISE.
WILL MAINTAIN A MENTION OF 4SM -SHSN BETWEEN 14-18Z. MVFR CEILINGS
WILL PERSIST ALONG WITH GUSTY WINDS THROUGH MUCH OF THE AFTERNOON
BEFORE VFR CONDITIONS RETURN BY 00Z AS CLOUD COVER GETS SCOURED
OUT BEHIND DEPARTING LOW PRESSURE.
KSAV...SATELLITE AND UPSTREAM OBSERVATIONS INDICATE LOW CLOUDS ARE
ON THE VERGE OF OVERSPREADING THE KSAV TERMINAL. EXPECT MVFR
CEILINGS TO OCCUR THERE SHORTLY AND PERSIST FOR MUCH OF THE DAY
ALONG WITH GUSTY WINDS. CEILINGS SHOULD RECOVER TO VFR BY MID
AFTERNOON AS CLOUD COVER BEGINS TO SCOUR OUT BEHIND DEPARTING LOW
PRESSURE. NO PRECIPITATION IS EXPECTED AT THE KSAV TERMINAL
OUTSIDE OF A FEW FLURRIES THIS MORNING...BUT CERTAINLY NOT ENOUGH
TO INCLUDE A MENTION ON THE 12Z TAF.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
FRIDAY NIGHT. COULD SEE MVFR CONDITIONS RETURN SATURDAY AS A COLD
FRONT PUSHES INTO THE AREA.
&&
.MARINE...
LARGE PRESSURE RISES ON THE BACKSIDE OF THE DEVELOPING SURFACE LOW
IS SUPPORTING GALE FORCE WINDS ACROSS MUCH OF NORTHEAST FLORIDA
AND SOUTHEAST GEORGIA OFFSHORE WATERS THIS MORNING. 41012 HAS
REPORTED WINDS IN EXCESS OF 40 KT OVER THE PAST FEW HOURS AND
41008 IS BEGINNING TO GUST TO GALE FORCE. HAVE RAISED A GALE
WARNING FOR OUR GEORGIA OFFSHORE LEG UNTIL 11 AM. THE GEORGIA
NEARSHORE WATERS ARE A TOUGH CALL BUT SUSPECT A STRONG SMALL CRAFT
ADVISORY WILL WORK THERE. FARTHER NORTH...WINDS WILL QUICKLY
INCREASE THIS MORNING AS THE LOW MOVES NORTHEAST OF THE REGION.
WILL MAINTAIN SMALL CRAFT ADVISORIES FOR THE SOUTH CAROLINA
NEARSHORE WATERS AND THE CHARLESTON HARBOR THROUGH LATE AFTERNOON.
BY TONIGHT...WINDS WILL WILL DIMINISH AS HIGH PRESSURE TRIES TO
BUILD IN FROM THE WEST. ONLY THE GEORGIA OFFSHORE WATERS LOOK TO
REMAIN WITHIN SMALL CRAFT ADVISORY THRESHOLDS.
WEDNESDAY THROUGH SUNDAY...HIGH PRESSURE WILL BUILD BACK INTO THE
REGION WEDNESDAY THROUGH FRIDAY...WITH THE NEXT COLD FRONT
EXPECTED TO APPROACH FROM THE WEST FRIDAY NIGHT AND PUSH THROUGH
THE MARINE AREA LATE SATURDAY. STRONG WEST WINDS EARLY WEDNESDAY
WILL GRADUALLY DIMINISH WITHIN BUILDING HIGH PRESSURE...THEN
BECOME SOUTHWEST AHEAD OF THE FRONT BY EARLY FRIDAY. GFS MODEL
DEVELOPS A TIGHT PRESSURE GRADIENT AS THE FRONT DROPS SOUTH
THROUGH THE AREA LATE SATURDAY...SUGGESTING WINDS AND SEAS COULD
REACH SMALL CRAFT ADVISORY CRITERIA.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR SCZ045.
WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
SCZ043>045.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ330-
350-352-354.
GALE WARNING UNTIL 11 AM EST THIS MORNING FOR AMZ374.
&&
$$
ST
000
FXUS62 KCHS 200849
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
349 AM EST TUE JAN 20 2009
.SYNOPSIS...
LOW PRESSURE ALONG THE SOUTH CAROLINA COAST WILL SHIFT NORTHEAST
OF THE AREA TODAY. HIGH PRESSURE WILL THEN BUILD BACK INTO THE
AREA TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT
MOVES INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /THROUGH TODAY/...
VERY DIFFICULT WINTER WEATHER FORECAST FOR THE FORECAST AREA TODAY.
A POTENT SHORTWAVE EVIDENT ON WATER VAPOR IMAGERY ACROSS SOUTHERN
MISSOURI WILL ROUND THE BASE OF THE AMPLIFYING LONG-WAVE TROUGH
TODAY. SURFACE OBSERVATIONS INDICATE CYCLOGENESIS IS WELL
UNDERWAY WITH THE CENTER OF THE LOW POSITIONED SOMEWHERE ACROSS
BERKELEY OR WILLIAMSBURG COUNTIES. SATELLITE TRENDS SUGGEST THE
SYSTEM IS BEGINNING TO RAPIDLY MATURE WITH WHAT APPEARS TO BE A
BAROCLINIC LEAF FORMING ALONG THE NORTH CAROLINA COAST. THE
SURFACE CYCLONE WILL STEADILY INTENSIFY THROUGH THE DAY AS UPPER
DIFLUENCE AHEAD OF THE APPROACHING SHORTWAVE INCREASES. COLD
CYCLONIC FLOW ON THE BACKSIDE OF THE DEPARTING LOW WILL HELP DRAG
COLD AND SOMEWHAT DRIER IN FROM THE NORTH THIS MORNING WITH WRAP
AROUND PRECIPITATION IMPACTING MAINLY THE NORTHERN HALF OF THE
FORECAST AREA. ALL OF OUR AVAILABLE SHORT TERM GUIDANCE SUGGESTS
RAIN WILL QUICKLY CHANGE TO SNOW AROUND SUNRISE AS SURFACE
TEMPERATURES RAPIDLY DROP WITH THERMAL PROFILES SUPPORTING SNOW
THROUGH THE AFTERNOON HOURS. THIS QUESTION NOW IS HOW MUCH
MEASURABLE SNOW WILL FALL.
IMPRESSIVE QUASIGEOSTROPHIC FORCING AHEAD OF THE APPROACHING
SHORTWAVE IS ALREADY SUPPORTING A FAIRLY LARGE SWATH OF LIGHT
RAIN AND SNOW STRETCHING FROM THE MIDLANDS THROUGH EASTERN NORTH
CAROLINA. MODELS SUGGEST THE STRONGEST FORCING AND HEAVIEST SNOW
WILL REMAIN TO THE NORTH WITH ONLY THE FAR NORTHERN COUNTIES
GETTING INTO THE FRINGES OF THE STRONGEST 850-700MB FRONTOGENETIC
ZONE. HOWEVER THE NAM/GFS/SREF AND 4-KM NSSL WRF ALL ROTATE A
FAIRLY HEALTHY AREA OF LIGHT SNOW INTO PORTIONS OF COLLETON-
DORCHESTER-BERKELEY AND CHARLESTON COUNTY LATER THIS MORNING.
GIVEN THE REFLECTIVITY TRENDS NOTED ON THE KCAE AND KGSP RADARS WE
HAVE NO REASON TO DISPUTE THIS...BUT THIS WILL BE A VERY CLOSE
CALL AS THE PRECIPITATION COULD VERY WELL PASS JUST TO THE NORTH
OF THESE COUNTIES. ATTM THE BEST CHANCES FOR MEASURABLE SNOW LOOKS
TO REMAIN ROUGHLY NORTH OF A LINE FROM SMOAKS TO WALTERBORO-
SUMMERVILLE-HUGER AND SHULERVILLE WITH ONLY TRACE AMOUNTS OR
FLURRIES FARTHER TO THE SOUTH. TOTAL ACCUMULATIONS LOOK TO BE NO
HIGHER THAN 1/2 TO 1 INCH AT BEST IN THESE AREAS AND MAINLY
CONFINED TO GRASSY SURFACES. THE SNOW LOOKS TO BECOME SOMEWHAT
CONVECTIVE BY MID-LATE MORNING AS MID-LEVEL LAPSE RATES STEEPEN SO
ISOLATED HIGHER AMOUNTS CAN NOT BE RULED OUT WHERE BURSTS OF
HEAVIER SNOW OCCUR. ITS INTERESTING TO NOTE THAT OUR LOCAL
WORKSTATION WRF MODEL DEVELOPS WHAT APPEARS TO BE A SMALL AREA OF
LAKE ENHANCED SNOWS DOWNWIND OF LAKES MOULTRIE AND MARION BY LATE
MORNING AS THERMAL PROFILES STEEPEN AND LOW-LEVEL TRAJECTORIES
TURN NORTHWEST. TOUGH CALL ON WHETHER THIS BANDED FEATURE WILL
FORM BUT ITS WORTH NOTING AS A SMALL AREA OF ENHANCED CONVECTIVE
SNOWS COULD CERTAINLY MATERIALIZE.
AFTER MUCH INTERNAL DISCUSSION AND COORDINATION WITH WFO/S ILM
AND CAE...WE PLAN TO CANCEL THE WINTER WEATHER ADVISORY FOR
JENKINS-SCREVEN-ALLENDALE AND HAMPTON COUNTIES AND MAINTAIN THE
ADVISORY UNTIL 5 PM THIS AFTERNOON FOR INLAND COLLETON-DORCHESTER
AND BERKELEY. CHARLESTON COUNTY IS STILL A TOSS UP...PARTICULARLY
FOR THE NORTH CHARLESTON AREA...BUT THERE IS JUST NOT ENOUGH
EVIDENCE IN THE AVAILABLE GUIDANCE TO SUPPORT AN EXPANSION INTO
THE CHARLESTON METRO AREA JUST YET. THIS COULD CERTAINLY CHANGE
LATER THIS MORNING AS MESOSCALE TRENDS BECOME MORE EVIDENT.
WILL GO WITH POPS AROUND 50 PERCENT ACROSS THE ADVISORY AREA
TAPERING TO 20 PERCENT ALONG THE SAVANNAH RIVER WITH POPS
DIMINISHING FROM SW-NE AS THE AFTERNOON PROGRESSES. ANY LINGERING
SNOW SHOWERS SHOULD DIMINISH TO FLURRIES ACROSS THE CHARLESTON
TRI-COUNTY AREA BY MID AFTERNOON.
HIGHS WILL BE EXTREMELY TRICKY TODAY AND WILL BE HIGHLY DEPENDANT
ON PRECIPITATION COVERAGE. WITH EVAPORATIONAL COOLING LIKELY TO
DOMINATE ACROSS THE NORTH WITH THE SNOW...THE COLDEST TEMPERATURES
WILL FOUND THERE WHILE FARTHER SOUTH SOME MORNING SUN MAY PRODUCE
A QUICK RISE IN TEMPERATURES SOUTH OF SAVANNAH. IN ADDITION SOME
AREAS ACROSS THE NORTH COULD SEE TEMPERATURES HOLD STEADY OR DROP
AFTER SUNRISE AS EVAPORATIONAL PROCESSES TAKE HOLD. WILL SHOW
HIGHS MID-UPPER 30S NORTH WITH UPPER 40S ACROSS THE FAR SOUTH BUT
FURTHER ADJUSTMENTS WILL LIKELY BE NEEDED LATER THIS MORNING.
LAKE WINDS...WINDS ARE EXPECTED TO INCREASE TO LAKE WIND ADVISORY
THRESHOLDS LATER THIS MORNING AS THE GRADIENT TIGHTENS ON THE
BACKSIDE OF DEPARTING LOW PRESSURE.
&&
.SHORT TERM /TONIGHT/...
CLEARING SKIES AND ONGOING COLD AIR ADVECTION WILL RESULT IN
CHILLY NIGHT ACROSS THE REGION WITH LOWS DROPPING INTO THE UPPER
TEENS WELL INLAND WITH MID 20S CLOSER TO THE COAST. COULD SEE
FLURRIES LINGER ACROSS BERKELEY AND CHARLESTON COUNTY UNTIL SUNSET
BUT NO ADDITIONAL ACCUMULATIONS WILL OCCUR. WIND CHILL VALUES WILL
DROP TO 10-15 INLAND AND CLOSER TO 15-20 ALONG THE COAST...WHICH
IS ABOVE WIND CHILL ADVISORY THRESHOLDS. ANY SNOW OR WET GROUNDS
THAT REMAIN AFTER SUNSET WILL QUICKLY REFREEZE AND THERE IS A
POSSIBILITY THAT BLACK ICE COULD BECOME AN ISSUE IN PLACES. THIS
WILL BE CAREFULLY MONITORED AS A WINTER WEATHER ADVISORY FOR BLACK
ICE MAY BE NEEDED.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE WEST ON
WEDNESDAY...AS THE AXIS OF THE DEEP UPPER TROUGH SHIFTS INTO THE
ATLANTIC. THIS PATTERN WILL ALLOW FOR RAIN FREE WEATHER AND A
WARMING TREND THROUGH LATE WEEK. HIGH TEMPERATURES WILL RETURN TO
NEAR SEASONAL NORMALS BY THURSDAY...REACHING THE UPPER 50S ACROSS
THE FORECAST AREA.
THE CENTER OF HIGH PRESSURE WILL GRADUALLY SLIP TO THE SOUTHEAST
BY FRIDAY...WHILE A COLD FRONT APPROACHES FROM THE WEST. THE REGION
WILL FALL WITHIN WARM SOUTHERLY FLOW AHEAD OF THE FRONT...AND EXPECT
HIGH TEMPERATURES TO REACH THE LOWER TO MID 60S WITHIN THE WARM
SECTOR FRIDAY.
THERE ARE SOME TIMING DIFFERENCES BETWEEN THE ECMWF AND GFS
REGARDING COLD FRONTAL PASSAGE OVER THE WEEKEND...WITH GFS BEING
THE FASTER OF THE TWO SOLUTIONS. AS A COMPROMISE BETWEEN THE
MODELS...HAVE INTRODUCED A SLIGHT CHANCE FOR SHOWERS AFTER
MIDNIGHT EARLY SATURDAY MORNING....WITH HIGHEST RAIN CHANCES LATER
ON SATURDAY. WILL CAP POPS AT 30 PERCENT...AS MODELS WILL LIKELY
ADJUST TIMING IN SUBSEQUENT RUNS.
DECREASE RAIN CHANCES FROM WEST TO EAST AS THE FRONT DROPS TO THE
SOUTHEAST OFFSHORE ON SUNDAY. GFS RAPIDLY BUILDS HIGH PRESSURE
DOWN FROM THE NORTH BEHIND THE FRONT ON SUNDAY...SETTING UP A
STRONG INLAND WEDGE/COASTAL TROUGH PATTERN. A QUICK GLANCE AT 00Z
ECMWF APPEARS TO SUGGEST IT ALSO COMING AROUND TO A SIMILAR
PATTERN. HAVE THUS REINTRODUCED SLIGHT CHANCE POPS ACROSS THE AREA
LATE SUNDAY NIGHT INTO MONDAY. COOLER HIGH TEMPERATURES IN THE 50S
ARE POSSIBLE WITHIN ANY INLAND WEDGE ON SUNDAY.
&&
.AVIATION /08Z TUESDAY THROUGH SATURDAY/...
VERY LIGHT RAIN IN THE VICINITY OF KCHS WILL MOVE QUICKLY OFF TO
THE NORTHEAST THROUGH 07Z WITH NO REDUCTIONS IN VISIBILITY.
CEILINGS ARE POISED TO BEGIN A SLOW DECLINE ACROSS THE REGION
OVERNIGHT AS LOW PRESSURE MOVES OFF THE SOUTH CAROLINA COAST AND
CYCLONIC FLOW IN ITS WAKE DRIVES COLDER AIR INTO THE REGION.
KCHS...EXPECT CEILINGS TO REACH LOW-END MVFR BY SUNRISE AS LIGHT
SNOW BLOSSOMS OVER THE MIDLANDS. AS THE LOW PULLS AWAY A BATCH OF
LIGHT SNOW IS EXPECTED TO DRIVE SOUTHEAST TOWARDS THE KCHS
TERMINAL...POSSIBLY DROPPING VISIBILITIES DOWN MVFR THRESHOLDS...
ROUGHLY IN THE 14-18Z TIME FRAME. SOME MINOR ACCUMULATIONS WILL BE
POSSIBLE AT THE TERMINAL...MAINLY ON GRASSY AREAS. THE SNOW WILL
GRADUALLY TAPPER TO FLURRIES DURING THE AFTERNOON BUT LOW CLOUDS
WILL REMAIN THROUGH MUCH OF THE DAY BEFORE SCOURING OUT THIS
EVENING.
KSAV...CAREFULLY WATCHING LARGE PRESSURE RISES ACROSS THE FLORIDA
PANHANDLE WHERE WINDS HAVE BEEN GUSTING CLOSE TO 20 KT. LOOKS LIKE
THE BULK OF THESE WINDS SHOULD REMAIN SOUTH OF KSAV BUT A DISTINCT
INCREASE IN SPEEDS IS LIKELY OVER THE NEXT FEW HOURS. CEILINGS
WILL ALSO DROP DOWN TO HIGH-END MVFR BY 10Z OR SO. NO PRECIPITATION
IS EXPECTED AT THE KSAV TERMINAL OUTSIDE OF A FEW FLURRIES THIS
MORNING...BUT CERTAINLY NOT ENOUGH TO INCLUDE A MENTION ON THE 06Z
TAF. LOW CLOUDS WILL PERSIST THROUGH MUCH OF THE AFTERNOON BEFORE
SOURING OUT THIS EVENING.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
FRIDAY NIGHT. COULD SEE MVFR CONDITIONS RETURN SATURDAY AS A COLD
FRONT PUSHES INTO THE AREA.
&&
.MARINE...
LARGE PRESSURE RISES ON THE BACKSIDE OF THE DEVELOPING SURFACE LOW
IS SUPPORTING GALE FORCE WINDS ACROSS MUCH OF NORTHEAST FLORIDA
AND SOUTHEAST GEORGIA OFFSHORE WATERS THIS MORNING. 41012 HAS
REPORTED WINDS IN EXCESS OF 40 KT OVER THE PAST FEW HOURS AND
41008 IS BEGINNING TO GUST TO GALE FORCE. HAVE RAISED A GALE
WARNING FOR OUR GEORGIA OFFSHORE LEG UNTIL 11 AM. THE GEORGIA
NEARSHORE WATERS ARE A TOUGH CALL BUT SUSPECT A STRONG SMALL CRAFT
ADVISORY WILL WORK THERE. FARTHER NORTH...WINDS WILL QUICKLY
INCREASE THIS MORNING AS THE LOW MOVES NORTHEAST OF THE REGION.
WILL MAINTAIN SMALL CRAFT ADVISORIES FOR THE SOUTH CAROLINA
NEARSHORE WATERS AND THE CHARLESTON HARBOR THROUGH LATE AFTERNOON.
BY TONIGHT...WINDS WILL WILL DIMINISH AS HIGH PRESSURE TRIES TO
BUILD IN FROM THE WEST. ONLY THE GEORGIA OFFSHORE WATERS LOOK TO
REMAIN WITHIN SMALL CRAFT ADVISORY THRESHOLDS.
WEDNESDAY THROUGH SUNDAY...HIGH PRESSURE WILL BUILD BACK INTO THE
REGION WEDNESDAY THROUGH FRIDAY...WITH THE NEXT COLD FRONT
EXPECTED TO APPROACH FROM THE WEST FRIDAY NIGHT AND PUSH THROUGH
THE MARINE AREA LATE SATURDAY. STRONG WEST WINDS EARLY WEDNESDAY
WILL GRADUALLY DIMINISH WITHIN BUILDING HIGH PRESSURE...THEN
BECOME SOUTHWEST AHEAD OF THE FRONT BY EARLY FRIDAY. GFS MODEL
DEVELOPS A TIGHT PRESSURE GRADIENT AS THE FRONT DROPS SOUTH
THROUGH THE AREA LATE SATURDAY...SUGGESTING WINDS AND SEAS COULD
REACH SMALL CRAFT ADVISORY CRITERIA.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR SCZ045.
WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
SCZ043>045.
MARINE...SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ330-
350-352-354.
GALE WARNING UNTIL 11 AM EST THIS MORNING FOR AMZ374.
&&
$$
ST/79
000
FXUS62 KCHS 200531
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1231 AM EST TUE JAN 20 2009
.SYNOPSIS...
LOW PRES WILL DEVELOP ALONG A COLD FRONT OVER THE ATLC LATE TONIGHT
AND EARLY TUESDAY...THEN SHIFTS NE TO OFF THE MID ATLC COAST DURING
THE AFTERNOON. HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA
TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT MOVES
INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
LATE MONDAY EVENING...A COLD FRONT WAS ADVANCING INTO WESTERN
COUNTIES OF THE FORECAST AREA. SURFACE LOWS WERE NOTED ON THE
BOUNDARY OVER THE SC MIDLANDS...AND OVER SE GA. THESE LOWS ARE
EXPECTED TO CONSOLIDATE INTO A SINGLE DOMINANT LOW PRESSURE ALONG
THE GA/SC COAST...IN THE VICINITY OF THE SAVANNAH RIVER
ENTRANCE...OVERNIGHT/EARLY TUE.
AHEAD OF THE COLD FRONT...DEEP LAYER FORCING/ASCENT SUPPORTED
SHOWERS/ISOLATED THUNDERSTORMS POISED TO ADVANCE THROUGH SE
GA...MAINLY S OF I-16...BY MIDNIGHT-1 AM. THEN...WRAP AROUND
MOISTURE ASSOCIATED WITH AN AMPLIFYING UPPER WAVE WILL ARRIVE
ACROSS INLAND COUNTIES AS COLDER AIR SPREADS INTO THE REGION
OVERNIGHT. AS A RESULT...ANY RAIN SHOULD CHANGE TO SNOW
SHOWERS...WITH A SLIGHT CHANCE FOR A BRIEF PERIOD OF FREEZING RAIN
DURING THE CHANGEOVER...ACROSS INLAND COUNTIES BEFORE DAYBREAK.
GIVEN PROGRESS OF UPSTREAM COLD AIR...MOVED START TIMES OF ONGOING
WINTER WEATHER ADVISORIES FROM HAMPTON/ALLENDALE COUNTIES EAST TO
BERKELEY COUNTY A COUPLE OF HOURS FROM THE AFTERNOON
PACKAGE...STARTING AT 3 AM WEST AND 4 AM EAST. ALSO...EXPANDED THE
WINTER WEATHER ADVISORY TO INCLUDE JENKINS/SCREVEN COUNTIES IN SE
GA...WHERE SNOW SHOWERS MAY PRODUCE SOME ACCUMULATION ON THE S
PERIPHERY OF THE WRAP AROUND REGIME.
PER COLLABORATION WITH WFO ILM...OPTED NOT TO EXPAND A WINTER
WEATHER ADVISORY INTO CHARLESTON COUNTY WITH THE MON EVENING
PACKAGE...AS COLD AIR/CHANGEOVER TO SNOW SHOWERS WILL ARRIVE LATEST...
TUESDAY MORNING.
LAKE WINDS...STRONG COLD AIR ADVECTION WILL BEGIN OVER LAKE
MOULTRIE LATE TONIGHT AS A TROUGH OF LOW PRESSURE MOVES THROUGH
THE AREA AND A STRONG STORM SYSTEM BEGINS TO ORGANIZE OFF THE
CAROLINA COAST. SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS
ARE EXPECTED LATE TONIGHT...THEREFORE WILL ISSUE A LAKE WIND
ADVISORY FOR LAKE MOULTRIE.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/...
WE HAVE INITIATED A WINTER WEATHER ADVISORY FOR SNOW ACROSS OUR
INLAND SC COUNTIES STARTING TUESDAY MORNING. AT THIS TIME HOWEVER
THAT DOES NOT INCLUDE CHARLESTON OR BEAUFORT COUNTIES...BUT THIS
COULD CHANGE DEPENDING UPON THE EVOLUTION OF THE SURFACE LOW AS IT
REACHES THE ATLC AND THE STRENGTH OF THE UPPER SHORT WAVE AND
ASSOCIATED DYNAMICS.
THE SURFACE LOW WILL STRENGTHEN AS IT MOVES ACROSS THE GULF STREAM
WATERS TUESDAY MORNING...WITH A CONTINUED INFLUX OF COLD AIR
MOVING IN FROM THE NW IN ITS WAKE. INDICATIONS ARE THAT ANY LIGHT
RAINS AND/OR MIXED PRECIP IN THE MORNING WILL CHANGE OVER TO ALL
SNOW BY AFTERNOON...AS THICKNESS...CROSS-SECTIONS...SOUNDINGS AND
WET BULBS ALL SUPPORT FROZEN PRECIP OVERSPREADING THE AREA.
AT 12Z...CONDITIONS OVERALL ARE TOO WARM AND TOO DRY TO SUPPORT
ANYTHING MORE THAN A LITTLE LIGHT RAIN...SNOW AND/OR FREEZING RAIN.
FROM 15Z TO 21Z...THE COLDER AIR IS OVERSPREADING THE AREA...WITH
A GRADUAL INCREASE IN MOISTURE. WHILE THE -10 TO -20C ICE GROWTH
ZONE HAS MOSTLY LESS THAN 80 PERCENT RH EARLY IN THIS TIME
PERIOD...IT DOES INCREASE TO AROUND 80 PERCENT OVER NORTHERN AND
WESTERN AREA BY AFTERNOON. SIGNIFICANT QG FORCING AT BOTH 700-500
MB AND 500-300 MB IS OCCURRING...WITH WEAK TO MODERATE LOW-MID
FRONTOGENESIS. ALSO...A 500-300 MB JET MOVES ACROSS THE AREA
DURING THE MORNING AND EARLY AFTERNOON. CROSS-SECTIONS ALSO SHOW
POSSIBLE BANDING OF SNOW DURING THIS TIME...WITH SATURATED EPV
ALONG WITH THE FRONTOGENESIS. THIS IS FURTHER SUPPORTED BY THE
ISENTROPIC TROWEL ANALYSIS WHICH SHOWS WEAK ISENTROPIC LIFT AT THE
290 AND 295K SURFACES DURING TUESDAY AFTERNOON...IN SYNC WITH THE
UPWARD OMEGA FIELDS.
GARCIA TECHNIQUE YIELDS ABOUT 1/2 TO 1 INCH OF SNOWFALL ACROSS
BEREKLEY...DORCHESTER...INLAND COLLETON...HAMPTON AND ALLENDALE
COUNTIES. HOWEVER...THE GROUND IS RELATIVELY WARM...WITH RECENT
SOIL TEMP AT KCHS STILL NEAR 50 DEGREES. WHILE THIS MIGHT POINT TO
SLIGHTLY LESS AMOUNTS...GIVEN THE POTENTIAL FOR HEAVIER BURSTS OF
SNOW WITH POSSIBLE CONVECTIVE BANDING...AND DECREASE IN SNOW
AMOUNTS DUE TO THE WARM GROUND SHOULD BE COMPENSATED FOR BY THE
POSSIBLE HEAVIER SNOWFALL. IN ADDITION...THE NW FETCH IS OFF LAKE
MOULTRIE AND LAKE MARION...OR FROM ABOUT 300-310 DEGREES.
TEMPERATURE DIFFERENCE BETWEEN THE AIR AND THE LAKE WILL BE ABOUT
10-12 DEGREES...WHICH LOOKS TO BE ENOUGH TO ALLOW FOR THE
POSSIBILITY OF A BAND OF SNOW DEVELOPING OVER THE LAKE WATERS
/SIMILAR TO LAKE EFFECT SNOWS IN THE GREAT LAKES/. SHOULD THIS
INDEED BECOME REALIZED...THEN SNOW AMOUNTS COULD BE LOCALLY HIGHER
DOWNWIND FROM THE LAKES.
FURTHER SOUTH AND EAST...WE HAVE OPTED TO KEEP CHARLESTON AND
BEAUFORT COUNTIES OUT OF THE ADVISORY. THE CURRENT THINKING IS
THAT THE BEST FORCING AND MOISTURE WILL REMAIN JUST NW OF BEAUFORT
COUNTY...AND WHILE WE DID CONSIDER INCLUDING CHARLESTON COUNTY IN
THE EARLIER ADVISORY...FOR COORDINATION PURPOSES WITH WFO ILM...WE
HAVE OPTED TO LEAVE THEM OUT AS WELL. THIS COULD CHANGE LATER
TONIGHT AFTER WE GET A BETTER HANDLE ON HOW THIS UNUSUAL SITUATION
WILL EVOLVE.
THE ADVISORY MAY NEED TO BE EXPANDED FURTHER SOUTH AND EAST LATER
TONIGHT OR EARLY TUESDAY...AND THERE IS EVEN THE POTENTIAL FOR AN
UPGRADE TO A WARNING. WHILE WE DO NOT EXPECT TO REACH OUR CRITERIA
OF 2 INCH SNOWFALL IN 12 HOURS...IT COULD BE PRUDENT TO ISSUE THE
WARNING FOR THE IMPACT...GIVEN HOW UNUSUAL THIS SITUATION IS.
MOST OF THE SNOWFALL WILL OCCUR ACROSS GRASSY SURFACES...ROOF TOPS
AND TREES...BUT IF HEAVIER SNOW BANDS DEVELOP...THEN SOME
ROADS...BRIDGES AND OVERPASSES COULD ALSO BECOME COVERED OR AT
LEAST SLICK.
THE SOUTHERN EXTENT OF THE SNOW WILL BE MAINLY THE I-16 CORRIDOR
IN SE GA...WITH THE POSSIBILITY OF FLURRIES EVEN AS FAR SOUTH AS
SAVANNAH...TYBEE ISLAND AND STATESBORO TUESDAY MORNING. SNOW WILL
TAPER OFF FROM SW TO NE DURING THE MID AND LATE AFTERNOON HOURS ON
TUESDAY AS THE ATLC LOW PULLS FURTHER AWAY...AND THE SHORT WAVE
BEGINS ITS EXIT OF THE AREA.
LITTLE CHANGE IN TEMPS ARE EXPECTED ACROSS NORTHERN AREAS ON
TUESDAY...WITH HIGHS GENERALLY IN THE 30S. CENTRAL AREAS WILL
REACH ONLY INTO THE LOWER 40S...WHILE OUR SOUTHERN AREAS WILL BE
THE WARMEST WITH READINGS IN THE MID TO UPPER 40S WHERE THE BEST
INSOLATION WILL OCCUR.
LAKE WINDS...CONTINUED STRONG COLD AIR ADVECTION OVER LAKE
MOULTRIE TUESDAY ACROSS THE WARMER LAKE WATERS WILL RESULT IN
SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS TUESDAY...THUS
A CONTINUATION OF THE LAKE WIND ADVISORY FOR LAKE MOULTRIE.
&&
.LONG TERM /TONIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EXTENDED
PERIOD THIS AFTERNOON...WITH ONLY A FEW MINOR DIFFERENCES NOTED OVER
THE WEEKEND AND INTO EARLY NEXT WEEK.
THE STRONG STORM SYSTEM WILL CONTINUE TO TRACK NORTHEASTWARD AND
AWAY FROM THE AREA TUESDAY NIGHT...WITH HIGH PRESSURE THEN BEGINNING
TO BUILD BACK INTO THE REGION. HAVE MENTIONED A SLIGHT CHANCE OF
FLURRIES IN THE EVENING ACROSS FAR NORTHERN ZONES AS DEEP
MOISTURE...SUFFICIENTLY COLD AIR ALOFT...AND DECENT FETCH OFF OF
LAKE MOULTRIE MAY BE ENOUGH TO KEEP A FEW SNOW FLAKES AROUND. ANY
LINGERING FLURRIES OR LIGHT SNOW SHOWERS SHOULD END IN THE
EVENING...WITH PRECIPITATION FREE WEATHER ANTICIPATED AFTER
MIDNIGHT.
HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA WEDNESDAY THROUGH
FRIDAY...RESULTING IN RAIN FREE WEATHER ACROSS THE REGION.
MODELS ARE IN GOOD AGREEMENT BRINGING A COLD FRONT SLOWLY THROUGH
THE REGION FRIDAY NIGHT THROUGH SATURDAY NIGHT...SO WILL CARRY
SLIGHT CHANCE/LOW CHANCE POPS FOR NOW UNTIL GUIDANCE GETS A BETTER
HANDLE ON TIMING DETAILS. HIGH PRESSURE IS THEN EXPECTED TO BUILD
FROM THE NORTH SUNDAY THROUGH MONDAY...WITH RAIN FREE WEATHER
ANTICIPATED.
&&
.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
VERY LIGHT RAIN IN THE VICINITY OF KCHS WILL MOVE QUICKLY OFF TO
THE NORTHEAST THROUGH 07Z WITH NO REDUCTIONS IN VISIBILITY.
CEILINGS ARE POISED TO BEGIN A SLOW DECLINE ACROSS THE REGION
OVERNIGHT AS LOW PRESSURE MOVES OFF THE SOUTH CAROLINA COAST AND
CYCLONIC FLOW IN ITS WAKE DRIVES COLDER AIR INTO THE REGION.
KCHS...EXPECT CEILINGS TO REACH LOW-END MVFR BY SUNRISE AS LIGHT
SNOW BLOSSOMS OVER THE MIDLANDS. AS THE LOW PULLS AWAY A BATCH OF
LIGHT SNOW IS EXPECTED TO DRIVE SOUTHEAST TOWARDS THE KCHS
TERMINAL...POSSIBLY DROPPING VISIBILITIES DOWN MVFR THRESHOLDS...
ROUGHLY IN THE 14-18Z TIME FRAME. SOME MINOR ACCUMULATIONS WILL BE
POSSIBLE AT THE TERMINAL...MAINLY ON GRASSY AREAS. THE SNOW WILL
GRADUALLY TAPPER TO FLURRIES DURING THE AFTERNOON BUT LOW CLOUDS
WILL REMAIN THROUGH MUCH OF THE DAY BEFORE SCOURING OUT THIS
EVENING.
KSAV...CAREFULLY WATCHING LARGE PRESSURE RISES ACROSS THE FLORIDA
PANHANDLE WHERE WINDS HAVE BEEN GUSTING CLOSE TO 20 KT. LOOKS LIKE
THE BULK OF THESE WINDS SHOULD REMAIN SOUTH OF KSAV BUT A DISTINCT
INCREASE IN SPEEDS IS LIKELY OVER THE NEXT FEW HOURS. CEILINGS
WILL ALSO DROP DOWN TO HIGH-END MVFR BY 10Z OR SO. NO PRECIPITATION
IS EXPECTED AT THE KSAV TERMINAL OUTSIDE OF A FEW FLURRIES THIS
MORNING...BUT CERTAINLY NOT ENOUGH TO INCLUDE A MENTION ON THE 06Z
TAF. LOW CLOUDS WILL PERSIST THROUGH MUCH OF THE AFTERNOON BEFORE
SOURING OUT THIS EVENING.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS ARE EXPECTED THROUGH
FRIDAY NIGHT. COULD SEE MVFR CONDITIONS RETURN SATURDAY AS A COLD
FRONT PUSHES INTO THE AREA.
&&
.MARINE...
A DEEPENING SURFACE TROUGH WAS APPROACHING THE COASTAL WATERS LATE
MON EVENING...AND WINDS ACROSS THE COASTAL WATERS WILL INCREASE
SIGNIFICANTLY OVERNIGHT AS SURFACE LOW PRESSURE CONSOLIDATES AND
INTENSIFIES NEAR THE ENTRANCE TO THE SAVANNAH RIVER. DUE THE
MON EVENING TRENDS...SUGGESTING A FASTER SYSTEM EVOLUTION...MOVED
UP THE START TIMES FOR ONGOING SMALL CRAFT ADVISORIES A COUPLE OF
HOURS FROM THE PREVIOUS FORECAST.
IN RESPONSE TO DEEPENING LOW PRESSURE ADVANCING NE...SCA
CONDITIONS WILL CONTINUE TO IMPACT THE MARINE AREA THROUGH TUESDAY
EVENING AS STRONG COLD AIR ADVECTION POURS INTO THE REGION.
THERE IS A SLIGHT CHANCE FOR A BRIEF PERIOD OF GALE FORCE GUSTS
ACROSS THE OUTER GA WATERS AND PERHAPS EVEN ACROSS THE SC
NEARSHORE WATERS TUES INTO TUE NIGHT.
HIGH PRESSURE WILL BUILD BACK INTO THE REGION WEDNESDAY THROUGH
FRIDAY...WITH THE NEXT COLD FRONT EXPECTED TO APPROACH FROM THE WEST
FRIDAY NIGHT AND PUSH THROUGH THE MARINE AREA ON SATURDAY. SEAS MAY
REMAIN IN THE SMALL CRAFT RANGE ACROSS THE OUTER GEORGIA WATERS
EARLY WEDNESDAY...OTHERWISE WINDS AND SEAS ARE EXPECTED TO REMAIN
BELOW HEADLINE THRESHOLDS WEDNESDAY THROUGH SATURDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...WINTER WEATHER ADVISORY UNTIL 1 PM EST THIS AFTERNOON FOR
GAZ087-088.
SC...LAKE WIND ADVISORY FROM 4 AM EARLY THIS MORNING TO 5 PM EST
THIS AFTERNOON FOR SCZ045.
WINTER WEATHER ADVISORY FROM 4 AM EARLY THIS MORNING TO 11 PM
EST THIS EVENING FOR SCZ044-045.
WINTER WEATHER ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR
SCZ040-042-043.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR AMZ350-
352.
SMALL CRAFT ADVISORY UNTIL 5 AM EST WEDNESDAY FOR AMZ354.
SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
SMALL CRAFT ADVISORY UNTIL 5 PM EST THIS AFTERNOON FOR AMZ330.
&&
$$
ST
000
FXUS62 KCHS 200304
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1004 PM EST MON JAN 19 2009
.SYNOPSIS...
LOW PRES WILL DEVELOP ALONG A COLD FRONT OVER THE ATLC LATE TONIGHT
AND EARLY TUESDAY...THEN SHIFTS NE TO OFF THE MID ATLC COAST DURING
THE AFTERNOON. HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA
TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT MOVES
INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
LATE MONDAY EVENING...A COLD FRONT WAS ADVANCING INTO WESTERN
COUNTIES OF THE FORECAST AREA. SURFACE LOWS WERE NOTED ON THE
BOUNDARY OVER THE SC MIDLANDS...AND OVER SE GA. THESE LOWS ARE
EXPECTED TO CONSOLIDATE INTO A SINGLE DOMINANT LOW PRESSURE ALONG
THE GA/SC COAST...IN THE VICINITY OF THE SAVANNAH RIVER
ENTRANCE...OVERNIGHT/EARLY TUE.
AHEAD OF THE COLD FRONT...DEEP LAYER FORCING/ASCENT SUPPORTED
SHOWERS/ISOLATED THUNDERSTORMS POISED TO ADVANCE THROUGH SE
GA...MAINLY S OF I-16...BY MIDNIGHT-1 AM. THEN...WRAP AROUND
MOISTURE ASSOCIATED WITH AN AMPLIFYING UPPER WAVE WILL ARRIVE
ACROSS INLAND COUNTIES AS COLDER AIR SPREADS INTO THE REGION
OVERNIGHT. AS A RESULT...ANY RAIN SHOULD CHANGE TO SNOW
SHOWERS...WITH A SLIGHT CHANCE FOR A BRIEF PERIOD OF FREEZING RAIN
DURING THE CHANGEOVER...ACROSS INLAND COUNTIES BEFORE DAYBREAK.
GIVEN PROGRESS OF UPSTREAM COLD AIR...MOVED START TIMES OF ONGOING
WINTER WEATHER ADVISORIES FROM HAMPTON/ALLENDALE COUNTIES EAST TO
BERKELEY COUNTY A COUPLE OF HOURS FROM THE AFTERNOON
PACKAGE...STARTING AT 3 AM WEST AND 4 AM EAST. ALSO...EXPANDED THE
WINTER WEATHER ADVISORY TO INCLUDE JENKINS/SCREVEN COUNTIES IN SE
GA...WHERE SNOW SHOWERS MAY PRODUCE SOME ACCUMULATION ON THE S
PERIPHERY OF THE WRAP AROUND REGIME.
PER COLLABORATION WITH WFO ILM...OPTED NOT TO EXPAND A WINTER
WEATHER ADVISORY INTO CHARLESTON COUNTY WITH THE MON EVENING
PACKAGE...AS COLD AIR/CHANGEOVER TO SNOW SHOWERS WILL ARRIVE LATEST...
TUESDAY MORNING.
LAKE WINDS...STRONG COLD AIR ADVECTION WILL BEGIN OVER LAKE
MOULTRIE LATE TONIGHT AS A TROUGH OF LOW PRESSURE MOVES THROUGH
THE AREA AND A STRONG STORM SYSTEM BEGINS TO ORGANIZE OFF THE
CAROLINA COAST. SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS
ARE EXPECTED LATE TONIGHT...THEREFORE WILL ISSUE A LAKE WIND
ADVISORY FOR LAKE MOULTRIE.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
WE HAVE INITIATED A WINTER WEATHER ADVISORY FOR SNOW ACROSS OUR
INLAND SC COUNTIES STARTING TUESDAY MORNING. AT THIS TIME HOWEVER
THAT DOES NOT INCLUDE CHARLESTON OR BEAUFORT COUNTIES...BUT THIS
COULD CHANGE DEPENDING UPON THE EVOLUTION OF THE SURFACE LOW AS IT
REACHES THE ATLC AND THE STRENGTH OF THE UPPER SHORT WAVE AND
ASSOCIATED DYNAMICS.
THE SURFACE LOW WILL STRENGTHEN AS IT MOVES ACROSS THE GULF STREAM
WATERS TUESDAY MORNING...WITH A CONTINUED INFLUX OF COLD AIR
MOVING IN FROM THE NW IN ITS WAKE. INDICATIONS ARE THAT ANY LIGHT
RAINS AND/OR MIXED PRECIP IN THE MORNING WILL CHANGE OVER TO ALL
SNOW BY AFTERNOON...AS THICKNESS...CROSS-SECTIONS...SOUNDINGS AND
WET BULBS ALL SUPPORT FROZEN PRECIP OVERSPREADING THE AREA.
AT 12Z...CONDITIONS OVERALL ARE TOO WARM AND TOO DRY TO SUPPORT
ANYTHING MORE THAN A LITTLE LIGHT RAIN...SNOW AND/OR FREEZING RAIN.
FROM 15Z TO 21Z...THE COLDER AIR IS OVERSPREADING THE AREA...WITH
A GRADUAL INCREASE IN MOISTURE. WHILE THE -10 TO -20C ICE GROWTH
ZONE HAS MOSTLY LESS THAN 80 PERCENT RH EARLY IN THIS TIME
PERIOD...IT DOES INCREASE TO AROUND 80 PERCENT OVER NORTHERN AND
WESTERN AREA BY AFTERNOON. SIGNIFICANT QG FORCING AT BOTH 700-500
MB AND 500-300 MB IS OCCURRING...WITH WEAK TO MODERATE LOW-MID
FRONTOGENESIS. ALSO...A 500-300 MB JET MOVES ACROSS THE AREA
DURING THE MORNING AND EARLY AFTERNOON. CROSS-SECTIONS ALSO SHOW
POSSIBLE BANDING OF SNOW DURING THIS TIME...WITH SATURATED EPV
ALONG WITH THE FRONTOGENESIS. THIS IS FURTHER SUPPORTED BY THE
ISENTROPIC TROWEL ANALYSIS WHICH SHOWS WEAK ISENTROPIC LIFT AT THE
290 AND 295K SURFACES DURING TUESDAY AFTERNOON...IN SYNC WITH THE
UPWARD OMEGA FIELDS.
GARCIA TECHNIQUE YIELDS ABOUT 1/2 TO 1 INCH OF SNOWFALL ACROSS
BEREKLEY...DORCHESTER...INLAND COLLETON...HAMPTON AND ALLENDALE
COUNTIES. HOWEVER...THE GROUND IS RELATIVELY WARM...WITH RECENT
SOIL TEMP AT KCHS STILL NEAR 50 DEGREES. WHILE THIS MIGHT POINT TO
SLIGHTLY LESS AMOUNTS...GIVEN THE POTENTIAL FOR HEAVIER BURSTS OF
SNOW WITH POSSIBLE CONVECTIVE BANDING...AND DECREASE IN SNOW
AMOUNTS DUE TO THE WARM GROUND SHOULD BE COMPENSATED FOR BY THE
POSSIBLE HEAVIER SNOWFALL. IN ADDITION...THE NW FETCH IS OFF LAKE
MOULTRIE AND LAKE MARION...OR FROM ABOUT 300-310 DEGREES.
TEMPERATURE DIFFERENCE BETWEEN THE AIR AND THE LAKE WILL BE ABOUT
10-12 DEGREES...WHICH LOOKS TO BE ENOUGH TO ALLOW FOR THE
POSSIBILITY OF A BAND OF SNOW DEVELOPING OVER THE LAKE WATERS
/SIMILAR TO LAKE EFFECT SNOWS IN THE GREAT LAKES/. SHOULD THIS
INDEED BECOME REALIZED...THEN SNOW AMOUNTS COULD BE LOCALLY HIGHER
DOWNWIND FROM THE LAKES.
FURTHER SOUTH AND EAST...WE HAVE OPTED TO KEEP CHARLESTON AND
BEAUFORT COUNTIES OUT OF THE ADVISORY. THE CURRENT THINKING IS
THAT THE BEST FORCING AND MOISTURE WILL REMAIN JUST NW OF BEAUFORT
COUNTY...AND WHILE WE DID CONSIDER INCLUDING CHARLESTON COUNTY IN
THE EARLIER ADVISORY...FOR COORDINATION PURPOSES WITH WFO ILM...WE
HAVE OPTED TO LEAVE THEM OUT AS WELL. THIS COULD CHANGE LATER
TONIGHT AFTER WE GET A BETTER HANDLE ON HOW THIS UNUSUAL SITUATION
WILL EVOLVE.
THE ADVISORY MAY NEED TO BE EXPANDED FURTHER SOUTH AND EAST LATER
TONIGHT OR EARLY TUESDAY...AND THERE IS EVEN THE POTENTIAL FOR AN
UPGRADE TO A WARNING. WHILE WE DO NOT EXPECT TO REACH OUR CRITERIA
OF 2 INCH SNOWFALL IN 12 HOURS...IT COULD BE PRUDENT TO ISSUE THE
WARNING FOR THE IMPACT...GIVEN HOW UNUSUAL THIS SITUATION IS.
MOST OF THE SNOWFALL WILL OCCUR ACROSS GRASSY SURFACES...ROOF TOPS
AND TREES...BUT IF HEAVIER SNOW BANDS DEVELOP...THEN SOME
ROADS...BRIDGES AND OVERPASSES COULD ALSO BECOME COVERED OR AT
LEAST SLICK.
THE SOUTHERN EXTENT OF THE SNOW WILL BE MAINLY THE I-16 CORRIDOR
IN SE GA...WITH THE POSSIBILITY OF FLURRIES EVEN AS FAR SOUTH AS
SAVANNAH...TYBEE ISLAND AND STATESBORO TUESDAY MORNING. SNOW WILL
TAPER OFF FROM SW TO NE DURING THE MID AND LATE AFTERNOON HOURS ON
TUESDAY AS THE ATLC LOW PULLS FURTHER AWAY...AND THE SHORT WAVE
BEGINS ITS EXIT OF THE AREA.
LITTLE CHANGE IN TEMPS ARE EXPECTED ACROSS NORTHERN AREAS ON
TUESDAY...WITH HIGHS GENERALLY IN THE 30S. CENTRAL AREAS WILL
REACH ONLY INTO THE LOWER 40S...WHILE OUR SOUTHERN AREAS WILL BE
THE WARMEST WITH READINGS IN THE MID TO UPPER 40S WHERE THE BEST
INSOLATION WILL OCCUR.
LAKE WINDS...CONTINUED STRONG COLD AIR ADVECTION OVER LAKE
MOULTRIE TUESDAY ACROSS THE WARMER LAKE WATERS WILL RESULT IN
SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS TUESDAY...THUS
A CONTINUATION OF THE LAKE WIND ADVISORY FOR LAKE MOULTRIE.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EXTENDED
PERIOD THIS AFTERNOON...WITH ONLY A FEW MINOR DIFFERENCES NOTED OVER
THE WEEKEND AND INTO EARLY NEXT WEEK.
THE STRONG STORM SYSTEM WILL CONTINUE TO TRACK NORTHEASTWARD AND
AWAY FROM THE AREA TUESDAY NIGHT...WITH HIGH PRESSURE THEN BEGINNING
TO BUILD BACK INTO THE REGION. HAVE MENTIONED A SLIGHT CHANCE OF
FLURRIES IN THE EVENING ACROSS FAR NORTHERN ZONES AS DEEP
MOISTURE...SUFFICIENTLY COLD AIR ALOFT...AND DECENT FETCH OFF OF
LAKE MOULTRIE MAY BE ENOUGH TO KEEP A FEW SNOW FLAKES AROUND. ANY
LINGERING FLURRIES OR LIGHT SNOW SHOWERS SHOULD END IN THE
EVENING...WITH PRECIPITATION FREE WEATHER ANTICIPATED AFTER
MIDNIGHT.
HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA WEDNESDAY THROUGH
FRIDAY...RESULTING IN RAIN FREE WEATHER ACROSS THE REGION.
MODELS ARE IN GOOD AGREEMENT BRINGING A COLD FRONT SLOWLY THROUGH
THE REGION FRIDAY NIGHT THROUGH SATURDAY NIGHT...SO WILL CARRY
SLIGHT CHANCE/LOW CHANCE POPS FOR NOW UNTIL GUIDANCE GETS A BETTER
HANDLE ON TIMING DETAILS. HIGH PRESSURE IS THEN EXPECTED TO BUILD
FROM THE NORTH SUNDAY THROUGH MONDAY...WITH RAIN FREE WEATHER
ANTICIPATED.
&&
.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
HAVE INTRODUCED A BRIEF PERIOD OF LIGHT RAIN AT KSAV AS THE
PRECIPITATION IS ACTUALLY REACHING THE SURFACE. SHOULD SEE THIS
ACTIVITY END WITHIN AN HOUR.
AS THE LOW PRESSURE SYSTEM DEVELOPS ALONG THE FRONT...CONDITIONS
WILL BE DETERIORATING AS THE LOW APPROACHES FROM THE WEST. EXPECT
BRIEF PERIODS OF LIGHT RAIN BETWEEN 06-10Z WITH MVFR CEILINGS AT
KCHS AIRPORT. THE RAIN WILL THEN CHANGE OVER TO LIGHT SNOW SHOWERS
BY MID-MORNING AND LASTING THROUGH EARLY TO MID-AFTERNOON. MVFR
OR LOWER VISIBILITIES IS EXPECTED DURING THE SNOW SHOWERS.
HOWEVER...ONLY INTRODUCED MVFR VISIBILITIES AT THIS TIME.
DRIER AIR WILL BEGIN FILTERING IN AS SOUTHWESTERLY WINDS BACK
TOWARD THE NORTHWEST IN THE AFTERNOON. WINDS WILL INCREASE 10 TO
15 KNOTS BY MID-MORNING AS THE LOW PRESSURE SYSTEM DEEPENS. HAVE
INTRODUCED VCSH FOR THE KSAV TERMINAL AS THE ACTIVITY WILL BECOME
MORE ISOLATED TO THE SOUTH. EXPECT MAINLY VFR CONDITIONS IN KSAV
WITH A POSSIBLE BRIEF PERIOD OF MVFR CEILINGS.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A BRIEF PERIOD OF MVFR
CONDITIONS TUESDAY EVENING AT THE CHARLESTON TERMINAL. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH FRIDAY NIGHT. COULD SEE MVFR
CONDITIONS RETURN SATURDAY AS A COLD FRONT PUSHES INTO THE AREA.
&&
.MARINE...
A DEEPENING SURFACE TROUGH WAS APPROACHING THE COASTAL WATERS LATE
MON EVENING...AND WINDS ACROSS THE COASTAL WATERS WILL INCREASE
SIGNIFICANTLY OVERNIGHT AS SURFACE LOW PRESSURE CONSOLIDATES AND
INTENSIFIES NEAR THE ENTRANCE TO THE SAVANNAH RIVER. DUE THE
MON EVENING TRENDS...SUGGESTING A FASTER SYSTEM EVOLUTION...MOVED
UP THE START TIMES FOR ONGOING SMALL CRAFT ADVISORIES A COUPLE OF
HOURS FROM THE PREVIOUS FORECAST.
IN RESPONSE TO DEEPENING LOW PRESSURE ADVANCING NE...SCA
CONDITIONS WILL CONTINUE TO IMPACT THE MARINE AREA THROUGH TUESDAY
EVENING AS STRONG COLD AIR ADVECTION POURS INTO THE REGION.
THERE IS A SLIGHT CHANCE FOR A BRIEF PERIOD OF GALE FORCE GUSTS
ACROSS THE OUTER GA WATERS AND PERHAPS EVEN ACROSS THE SC
NEARSHORE WATERS TUES INTO TUE NIGHT.
HIGH PRESSURE WILL BUILD BACK INTO THE REGION WEDNESDAY THROUGH
FRIDAY...WITH THE NEXT COLD FRONT EXPECTED TO APPROACH FROM THE WEST
FRIDAY NIGHT AND PUSH THROUGH THE MARINE AREA ON SATURDAY. SEAS MAY
REMAIN IN THE SMALL CRAFT RANGE ACROSS THE OUTER GEORGIA WATERS
EARLY WEDNESDAY...OTHERWISE WINDS AND SEAS ARE EXPECTED TO REMAIN
BELOW HEADLINE THRESHOLDS WEDNESDAY THROUGH SATURDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...WINTER WEATHER ADVISORY FROM 3 AM TO 1 PM EST TUESDAY FOR
GAZ087-088.
SC...LAKE WIND ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR SCZ045.
WINTER WEATHER ADVISORY FROM 4 AM TO 11 PM EST TUESDAY FOR
SCZ044-045.
WINTER WEATHER ADVISORY FROM 3 AM TO 5 PM EST TUESDAY FOR
SCZ040-042-043.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EST TUESDAY FOR AMZ350-352.
SMALL CRAFT ADVISORY UNTIL 5 AM EST WEDNESDAY FOR AMZ354.
SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 2 AM TO 5 PM EST TUESDAY FOR AMZ330.
&&
$$
000
FXUS62 KCHS 192357
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
657 PM EST MON JAN 19 2009
.SYNOPSIS...
LOW PRES WILL DEVELOP ALONG A COLD FRONT OVER THE ATLC LATE TONIGHT
AND EARLY TUESDAY...THEN SHIFTS NE TO OFF THE MID ATLC COAST DURING
THE AFTERNOON. HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA
TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT MOVES
INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
SHORT WAVE NOW MOVING THROUGH THE TN VALLEY AND THE SOUTHERN
APPALACHIANS WILL PUSH THROUGH THE AREA TONIGHT...BRINGING WITH IT
PLENTY OF CLOUDS EARLY TONIGHT AND A SLIGHT CHANCE OF RAIN.
ALREADY WE ARE SEEING CONSIDERABLE RADAR RETURNS...BUT THEY ARE
STILL JUST LOW TO MID LEVEL CLOUDS WITH THE AIR MASS STILL SO DRY.
DEW POINT DEPRESSIONS ARE 20 DEGREES OR HIGHER AS OF MID
AFTERNOON...THUS IT WILL BE AWHILE BEFORE THINGS MOISTEN UP. BUT A
LITTLE CONVECTIVE PRECIP WILL DEVELOP THIS EVENING RESULTING IN SOME
LIGHT RAINS.
AS THE SHORT WAVES MOVES ACROSS THE AREA TONIGHT IT WILL DEVELOP A
SURFACE LOW PRES SYSTEM OVER CENTRAL AND SOUTHERN SC...WHICH
SHIFTS EAST. THIS LOW WILL DEVELOP FURTHER AS IT REACHES THE
WARMER ATLC WATERS LATE TONIGHT...WITH COLDER AIR TO FUNNEL IN ON
THE BACKSIDE OF THE LOW. STRONG UPWARD OMEGA AND 500-300 MB
Q-VECTOR CONVERGENCE AND INCREASING ISENTROPIC LIFT WILL SUPPORT
SLIGHT CHANCE TO CHANCE POPS MAINLY ACROSS THE CENTRAL AND
NORTHERN CWFA IN CLOSER PROXIMITY TO THE SURFACE LOW. WHILE MOST
OF THE PRECIP TONIGHT WILL BE IN LIQUID FORM...THERE MAY BE A
LITTLE FREEZING PRECIP FAR INLAND LATE AS TEMPS FALL TO NEAR 32
DEGREES. THIS IS MAINLY IN THE AREA FROM SAINT GEORGE TO
WILLIAMS...TO ALLENDALE...HILLTONIA AND MILLEN.
IN ADDITION...SOUNDINGS INDICATE THAT THE COLDER AIR WILL
PENETRATE ENOUGH INTO THE NW ZONES BY MORNING TO ALLOW FOR SOME
LIGHT SNOW TO ALSO MIX IN WITH THE RAIN AND FREEZING RAIN. NO
ACCUMULATION OF ICE OR SNOW WILL OCCUR BY MORNING...BUT MOTORISTS
SHOULD STILL USE EXTREME CARE DUE TO THE WET ROADS...AND KEEP IN
MIND THAT SHOULD TEMPS DROP BELOW FREEZING THAT MINOR ICING WOULD
OCCUR ACROSS SOME OF THE ELEVATED ROAD SURFACE SUCH AS OVERPASSES
AND BRIDGES.
LOW TEMPS FURTHER SE TONIGHT WILL BE IN THE MID AND UPPER 30S...SO
NO CONCERNS FOR WINTER PRECIP ACROSS THE VAST MAJORITY OF THE
FORECAST AREA.
LAKE WINDS...STRONG COLD AIR ADVECTION WILL BEGIN OVER LAKE
MOULTRIE LATE TONIGHT AS A TROUGH OF LOW PRESSURE MOVES THROUGH
THE AREA AND A STRONG STORM SYSTEM BEGINS TO ORGANIZE OFF THE
CAROLINA COAST. SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS
ARE EXPECTED LATE TONIGHT...THEREFORE WILL ISSUE A LAKE WIND
ADVISORY FOR LAKE MOULTRIE.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
WE HAVE INITIATED A WINTER WEATHER ADVISORY FOR SNOW ACROSS OUR
INLAND SC COUNTIES STARTING TUESDAY MORNING. AT THIS TIME HOWEVER
THAT DOES NOT INCLUDE CHARLESTON OR BEAUFORT COUNTIES...BUT THIS
COULD CHANGE DEPENDING UPON THE EVOLUTION OF THE SURFACE LOW AS IT
REACHES THE ATLC AND THE STRENGTH OF THE UPPER SHORT WAVE AND
ASSOCIATED DYNAMICS.
THE SURFACE LOW WILL STRENGTHEN AS IT MOVES ACROSS THE GULF STREAM
WATERS TUESDAY MORNING...WITH A CONTINUED INFLUX OF COLD AIR
MOVING IN FROM THE NW IN ITS WAKE. INDICATIONS ARE THAT ANY LIGHT
RAINS AND/OR MIXED PRECIP IN THE MORNING WILL CHANGE OVER TO ALL
SNOW BY AFTERNOON...AS THICKNESS...CROSS-SECTIONS...SOUNDINGS AND
WET BULBS ALL SUPPORT FROZEN PRECIP OVERSPREADING THE AREA.
AT 12Z...CONDITIONS OVERALL ARE TOO WARM AND TOO DRY TO SUPPORT
ANYTHING MORE THAN A LITTLE LIGHT RAIN...SNOW AND/OR FREEZING RAIN.
FROM 15Z TO 21Z...THE COLDER AIR IS OVERSPREADING THE AREA...WITH
A GRADUAL INCREASE IN MOISTURE. WHILE THE -10 TO -20C ICE GROWTH
ZONE HAS MOSTLY LESS THAN 80 PERCENT RH EARLY IN THIS TIME
PERIOD...IT DOES INCREASE TO AROUND 80 PERCENT OVER NORTHERN AND
WESTERN AREA BY AFTERNOON. SIGNIFICANT QG FORCING AT BOTH 700-500
MB AND 500-300 MB IS OCCURRING...WITH WEAK TO MODERATE LOW-MID
FRONTOGENESIS. ALSO...A 500-300 MB JET MOVES ACROSS THE AREA
DURING THE MORNING AND EARLY AFTERNOON. CROSS-SECTIONS ALSO SHOW
POSSIBLE BANDING OF SNOW DURING THIS TIME...WITH SATURATED EPV
ALONG WITH THE FRONTOGENESIS. THIS IS FURTHER SUPPORTED BY THE
ISENTROPIC TROWEL ANALYSIS WHICH SHOWS WEAK ISENTROPIC LIFT AT THE
290 AND 295K SURFACES DURING TUESDAY AFTERNOON...IN SYNC WITH THE
UPWARD OMEGA FIELDS.
GARCIA TECHNIQUE YIELDS ABOUT 1/2 TO 1 INCH OF SNOWFALL ACROSS
BEREKLEY...DORCHESTER...INLAND COLLETON...HAMPTON AND ALLENDALE
COUNTIES. HOWEVER...THE GROUND IS RELATIVELY WARM...WITH RECENT
SOIL TEMP AT KCHS STILL NEAR 50 DEGREES. WHILE THIS MIGHT POINT TO
SLIGHTLY LESS AMOUNTS...GIVEN THE POTENTIAL FOR HEAVIER BURSTS OF
SNOW WITH POSSIBLE CONVECTIVE BANDING...AND DECREASE IN SNOW
AMOUNTS DUE TO THE WARM GROUND SHOULD BE COMPENSATED FOR BY THE
POSSIBLE HEAVIER SNOWFALL. IN ADDITION...THE NW FETCH IS OFF LAKE
MOULTRIE AND LAKE MARION...OR FROM ABOUT 300-310 DEGREES.
TEMPERATURE DIFFERENCE BETWEEN THE AIR AND THE LAKE WILL BE ABOUT
10-12 DEGREES...WHICH LOOKS TO BE ENOUGH TO ALLOW FOR THE
POSSIBILITY OF A BAND OF SNOW DEVELOPING OVER THE LAKE WATERS
/SIMILAR TO LAKE EFFECT SNOWS IN THE GREAT LAKES/. SHOULD THIS
INDEED BECOME REALIZED...THEN SNOW AMOUNTS COULD BE LOCALLY HIGHER
DOWNWIND FROM THE LAKES.
FURTHER SOUTH AND EAST...WE HAVE OPTED TO KEEP CHARLESTON AND
BEAUFORT COUNTIES OUT OF THE ADVISORY. THE CURRENT THINKING IS
THAT THE BEST FORCING AND MOISTURE WILL REMAIN JUST NW OF BEAUFORT
COUNTY...AND WHILE WE DID CONSIDER INCLUDING CHARLESTON COUNTY IN
THE EARLIER ADVISORY...FOR COORDINATION PURPOSES WITH WFO ILM...WE
HAVE OPTED TO LEAVE THEM OUT AS WELL. THIS COULD CHANGE LATER
TONIGHT AFTER WE GET A BETTER HANDLE ON HOW THIS UNUSUAL SITUATION
WILL EVOLVE.
THE ADVISORY MAY NEED TO BE EXPANDED FURTHER SOUTH AND EAST LATER
TONIGHT OR EARLY TUESDAY...AND THERE IS EVEN THE POTENTIAL FOR AN
UPGRADE TO A WARNING. WHILE WE DO NOT EXPECT TO REACH OUR CRITERIA
OF 2 INCH SNOWFALL IN 12 HOURS...IT COULD BE PRUDENT TO ISSUE THE
WARNING FOR THE IMPACT...GIVEN HOW UNUSUAL THIS SITUATION IS.
MOST OF THE SNOWFALL WILL OCCUR ACROSS GRASSY SURFACES...ROOF TOPS
AND TREES...BUT IF HEAVIER SNOW BANDS DEVELOP...THEN SOME
ROADS...BRIDGES AND OVERPASSES COULD ALSO BECOME COVERED OR AT
LEAST SLICK.
THE SOUTHERN EXTENT OF THE SNOW WILL BE MAINLY THE I-16 CORRIDOR
IN SE GA...WITH THE POSSIBILITY OF FLURRIES EVEN AS FAR SOUTH AS
SAVANNAH...TYBEE ISLAND AND STATESBORO TUESDAY MORNING. SNOW WILL
TAPER OFF FROM SW TO NE DURING THE MID AND LATE AFTERNOON HOURS ON
TUESDAY AS THE ATLC LOW PULLS FURTHER AWAY...AND THE SHORT WAVE
BEGINS ITS EXIT OF THE AREA.
LITTLE CHANGE IN TEMPS ARE EXPECTED ACROSS NORTHERN AREAS ON
TUESDAY...WITH HIGHS GENERALLY IN THE 30S. CENTRAL AREAS WILL
REACH ONLY INTO THE LOWER 40S...WHILE OUR SOUTHERN AREAS WILL BE
THE WARMEST WITH READINGS IN THE MID TO UPPER 40S WHERE THE BEST
INSOLATION WILL OCCUR.
LAKE WINDS...CONTINUED STRONG COLD AIR ADVECTION OVER LAKE
MOULTRIE TUESDAY ACROSS THE WARMER LAKE WATERS WILL RESULT IN
SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS TUESDAY...THUS
A CONTINUATION OF THE LAKE WIND ADVISORY FOR LAKE MOULTRIE.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EXTENDED
PERIOD THIS AFTERNOON...WITH ONLY A FEW MINOR DIFFERENCES NOTED OVER
THE WEEKEND AND INTO EARLY NEXT WEEK.
THE STRONG STORM SYSTEM WILL CONTINUE TO TRACK NORTHEASTWARD AND
AWAY FROM THE AREA TUESDAY NIGHT...WITH HIGH PRESSURE THEN BEGINNING
TO BUILD BACK INTO THE REGION. HAVE MENTIONED A SLIGHT CHANCE OF
FLURRIES IN THE EVENING ACROSS FAR NORTHERN ZONES AS DEEP
MOISTURE...SUFFICIENTLY COLD AIR ALOFT...AND DECENT FETCH OFF OF
LAKE MOULTRIE MAY BE ENOUGH TO KEEP A FEW SNOW FLAKES AROUND. ANY
LINGERING FLURRIES OR LIGHT SNOW SHOWERS SHOULD END IN THE
EVENING...WITH PRECIPITATION FREE WEATHER ANTICIPATED AFTER
MIDNIGHT.
HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA WEDNESDAY THROUGH
FRIDAY...RESULTING IN RAIN FREE WEATHER ACROSS THE REGION.
MODELS ARE IN GOOD AGREEMENT BRINGING A COLD FRONT SLOWLY THROUGH
THE REGION FRIDAY NIGHT THROUGH SATURDAY NIGHT...SO WILL CARRY
SLIGHT CHANCE/LOW CHANCE POPS FOR NOW UNTIL GUIDANCE GETS A BETTER
HANDLE ON TIMING DETAILS. HIGH PRESSURE IS THEN EXPECTED TO BUILD
FROM THE NORTH SUNDAY THROUGH MONDAY...WITH RAIN FREE WEATHER
ANTICIPATED.
&&
.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
HAVE INTRODUCED A BRIEF PERIOD OF LIGHT RAIN AT KSAV AS THE
PRECIPITATION IS ACTUALLY REACHING THE SURFACE. SHOULD SEE THIS
ACTIVITY END WITHIN AN HOUR.
AS THE LOW PRESSURE SYSTEM DEVELOPS ALONG THE FRONT...CONDITIONS
WILL BE DETERIORATING AS THE LOW APPROACHES FROM THE WEST. EXPECT
BRIEF PERIODS OF LIGHT RAIN BETWEEN 06-10Z WITH MVFR CEILINGS AT
KCHS AIRPORT. THE RAIN WILL THEN CHANGE OVER TO LIGHT SNOW SHOWERS
BY MID-MORNING AND LASTING THROUGH EARLY TO MID-AFTERNOON. MVFR
OR LOWER VISIBILITIES IS EXPECTED DURING THE SNOW SHOWERS.
HOWEVER...ONLY INTRODUCED MVFR VISIBILITIES AT THIS TIME.
DRIER AIR WILL BEGIN FILTERING IN AS SOUTHWESTERLY WINDS BACK
TOWARD THE NORTHWEST IN THE AFTERNOON. WINDS WILL INCREASE 10 TO
15 KNOTS BY MID-MORNING AS THE LOW PRESSURE SYSTEM DEEPENS. HAVE
INTRODUCED VCSH FOR THE KSAV TERMINAL AS THE ACTIVITY WILL BECOME
MORE ISOLATED TO THE SOUTH. EXPECT MAINLY VFR CONDITIONS IN KSAV
WITH A POSSIBLE BRIEF PERIOD OF MVFR CEILINGS.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A BRIEF PERIOD OF MVFR
CONDITIONS TUESDAY EVENING AT THE CHARLESTON TERMINAL. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH FRIDAY NIGHT. COULD SEE MVFR
CONDITIONS RETURN SATURDAY AS A COLD FRONT PUSHES INTO THE AREA.
&&
.MARINE...
A TROUGH OF LOW PRESSURE WILL MOVE THROUGH THE WATERS OVERNIGHT...AS
A STORM SYSTEM BEGINS TO ORGANIZE OFF THE CAROLINA COAST. WINDS ARE
EXPECTED TO INCREASE OVER THE COASTAL WATERS AHEAD OF THE
APPROACHING TROUGH OF LOW PRESSURE...AND CONTINUE TO IMPACT THE
MARINE AREA THROUGH TUESDAY EVENING AS STRONG COLD AIR ADVECTION
POURS IN BEHIND THE DEPARTING STORM SYSTEM. HAVE RAISED SMALL CRAFT
ADVISORIES FOR ALL WATERS BEGINNING LATE THIS EVENING OR AFTER
MIDNIGHT...AND CONTINUING THROUGH LATE TUESDAY AFTERNOON OR TUESDAY
EVENING MOST WATERS.
HIGH PRESSURE WILL BUILD BACK INTO THE REGION WEDNESDAY THROUGH
FRIDAY...WITH THE NEXT COLD FRONT EXPECTED TO APPROACH FROM THE WEST
FRIDAY NIGHT AND PUSH THROUGH THE MARINE AREA ON SATURDAY. SEAS MAY
REMAIN IN THE SMALL CRAFT RANGE ACROSS THE OUTER GEORGIA WATERS
EARLY WEDNESDAY...OTHERWISE WINDS AND SEAS ARE EXPECTED TO REMAIN
BELOW HEADLINE THRESHOLDS WEDNESDAY THROUGH SATURDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR SCZ045.
WINTER WEATHER ADVISORY FROM 8 AM TO 10 PM EST TUESDAY FOR
SCZ044-045.
WINTER WEATHER ADVISORY FROM 6 AM TO 5 PM EST TUESDAY FOR
SCZ040-042-043.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 11 PM EST TUESDAY FOR AMZ350-
352.
SMALL CRAFT ADVISORY FROM 1 AM TUESDAY TO 5 AM EST WEDNESDAY
FOR AMZ354.
SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EST
WEDNESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR AMZ330.
&&
$$
000
FXUS62 KCHS 192203
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
456 PM EST MON JAN 19 2009
...WINTER WEATHER LIKELY IN MANY AREAS TUESDAY...
.SYNOPSIS...
LOW PRES WILL DEVELOP ALONG A COLD FRONT OVER THE ATLC LATE TONIGHT
AND EARLY TUESDAY...THEN SHIFTS NE TO OFF THE MID ATLC COAST DURING
THE AFTERNOON. HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA
TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT MOVES
INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
SHORT WAVE NOW MOVING THROUGH THE TN VALLEY AND THE SOUTHERN
APPALACHIANS WILL PUSH THROUGH THE AREA TONIGHT...BRINGING WITH IT
PLENTY OF CLOUDS EARLY TONIGHT AND A SLIGHT CHANCE OF RAIN.
ALREADY WE ARE SEEING CONSIDERABLE RADAR RETURNS...BUT THEY ARE
STILL JUST LOW TO MID LEVEL CLOUDS WITH THE AIR MASS STILL SO DRY.
DEW POINT DEPRESSIONS ARE 20 DEGREES OR HIGHER AS OF MID
AFTERNOON...THUS IT WILL BE AWHILE BEFORE THINGS MOISTEN UP. BUT A
LITTLE CONVECTIVE PRECIP WILL DEVELOP THIS EVENING RESULTING IN SOME
LIGHT RAINS.
AS THE SHORT WAVES MOVES ACROSS THE AREA TONIGHT IT WILL DEVELOP A
SURFACE LOW PRES SYSTEM OVER CENTRAL AND SOUTHERN SC...WHICH
SHIFTS EAST. THIS LOW WILL DEVELOP FURTHER AS IT REACHES THE
WARMER ATLC WATERS LATE TONIGHT...WITH COLDER AIR TO FUNNEL IN ON
THE BACKSIDE OF THE LOW. STRONG UPWARD OMEGA AND 500-300 MB
Q-VECTOR CONVERGENCE AND INCREASING ISENTROPIC LIFT WILL SUPPORT
SLIGHT CHANCE TO CHANCE POPS MAINLY ACROSS THE CENTRAL AND
NORTHERN CWFA IN CLOSER PROXIMITY TO THE SURFACE LOW. WHILE MOST
OF THE PRECIP TONIGHT WILL BE IN LIQUID FORM...THERE MAY BE A
LITTLE FREEZING PRECIP FAR INLAND LATE AS TEMPS FALL TO NEAR 32
DEGREES. THIS IS MAINLY IN THE AREA FROM SAINT GEORGE TO
WILLIAMS...TO ALLENDALE...HILLTONIA AND MILLEN.
IN ADDITION...SOUNDINGS INDICATE THAT THE COLDER AIR WILL
PENETRATE ENOUGH INTO THE NW ZONES BY MORNING TO ALLOW FOR SOME
LIGHT SNOW TO ALSO MIX IN WITH THE RAIN AND FREEZING RAIN. NO
ACCUMULATION OF ICE OR SNOW WILL OCCUR BY MORNING...BUT MOTORISTS
SHOULD STILL USE EXTREME CARE DUE TO THE WET ROADS...AND KEEP IN
MIND THAT SHOULD TEMPS DROP BELOW FREEZING THAT MINOR ICING WOULD
OCCUR ACROSS SOME OF THE ELEVATED ROAD SURFACE SUCH AS OVERPASSES
AND BRIDGES.
LOW TEMPS FURTHER SE TONIGHT WILL BE IN THE MID AND UPPER 30S...SO
NO CONCERNS FOR WINTER PRECIP ACROSS THE VAST MAJORITY OF THE
FORECAST AREA.
LAKE WINDS...STRONG COLD AIR ADVECTION WILL BEGIN OVER LAKE
MOULTRIE LATE TONIGHT AS A TROUGH OF LOW PRESSURE MOVES THROUGH
THE AREA AND A STRONG STORM SYSTEM BEGINS TO ORGANIZE OFF THE
CAROLINA COAST. SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS
ARE EXPECTED LATE TONIGHT...THEREFORE WILL ISSUE A LAKE WIND
ADVISORY FOR LAKE MOULTRIE.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
WE HAVE INITIATED A WINTER WEATHER ADVISORY FOR SNOW ACROSS OUR
INLAND SC COUNTIES STARTING TUESDAY MORNING. AT THIS TIME HOWEVER
THAT DOES NOT INCLUDE CHARLESTON OR BEAUFORT COUNTIES...BUT THIS
COULD CHANGE DEPENDING UPON THE EVOLUTION OF THE SURFACE LOW AS IT
REACHES THE ATLC AND THE STRENGTH OF THE UPPER SHORT WAVE AND
ASSOCIATED DYNAMICS.
THE SURFACE LOW WILL STRENGTHEN AS IT MOVES ACROSS THE GULF STREAM
WATERS TUESDAY MORNING...WITH A CONTINUED INFLUX OF COLD AIR
MOVING IN FROM THE NW IN ITS WAKE. INDICATIONS ARE THAT ANY LIGHT
RAINS AND/OR MIXED PRECIP IN THE MORNING WILL CHANGE OVER TO ALL
SNOW BY AFTERNOON...AS THICKNESS...CROSS-SECTIONS...SOUNDINGS AND
WET BULBS ALL SUPPORT FROZEN PRECIP OVERSPREADING THE AREA.
AT 12Z...CONDITIONS OVERALL ARE TOO WARM AND TOO DRY TO SUPPORT
ANYTHING MORE THAN A LITTLE LIGHT RAIN...SNOW AND/OR FREEZING RAIN.
FROM 15Z TO 21Z...THE COLDER AIR IS OVERSPREADING THE AREA...WITH
A GRADUAL INCREASE IN MOISTURE. WHILE THE -10 TO -20C ICE GROWTH
ZONE HAS MOSTLY LESS THAN 80 PERCENT RH EARLY IN THIS TIME
PERIOD...IT DOES INCREASE TO AROUND 80 PERCENT OVER NORTHERN AND
WESTERN AREA BY AFTERNOON. SIGNIFICANT QG FORCING AT BOTH 700-500
MB AND 500-300 MB IS OCCURRING...WITH WEAK TO MODERATE LOW-MID
FRONTOGENESIS. ALSO...A 500-300 MB JET MOVES ACROSS THE AREA
DURING THE MORNING AND EARLY AFTERNOON. CROSS-SECTIONS ALSO SHOW
POSSIBLE BANDING OF SNOW DURING THIS TIME...WITH SATURATED EPV
ALONG WITH THE FRONTOGENESIS. THIS IS FURTHER SUPPORTED BY THE
ISENTROPIC TROWEL ANALYSIS WHICH SHOWS WEAK ISENTROPIC LIFT AT THE
290 AND 295K SURFACES DURING TUESDAY AFTERNOON...IN SYNC WITH THE
UPWARD OMEGA FIELDS.
GARCIA TECHNIQUE YIELDS ABOUT 1/2 TO 1 INCH OF SNOWFALL ACROSS
BEREKLEY...DORCHESTER...INLAND COLLETON...HAMPTON AND ALLENDALE
COUNTIES. HOWEVER...THE GROUND IS RELATIVELY WARM...WITH RECENT
SOIL TEMP AT KCHS STILL NEAR 50 DEGREES. WHILE THIS MIGHT POINT TO
SLIGHTLY LESS AMOUNTS...GIVEN THE POTENTIAL FOR HEAVIER BURSTS OF
SNOW WITH POSSIBLE CONVECTIVE BANDING...AND DECREASE IN SNOW
AMOUNTS DUE TO THE WARM GROUND SHOULD BE COMPENSATED FOR BY THE
POSSIBLE HEAVIER SNOWFALL. IN ADDITION...THE NW FETCH IS OFF LAKE
MOULTRIE AND LAKE MARION...OR FROM ABOUT 300-310 DEGREES.
TEMPERATURE DIFFERENCE BETWEEN THE AIR AND THE LAKE WILL BE ABOUT
10-12 DEGREES...WHICH LOOKS TO BE ENOUGH TO ALLOW FOR THE
POSSIBILITY OF A BAND OF SNOW DEVELOPING OVER THE LAKE WATERS
/SIMILAR TO LAKE EFFECT SNOWS IN THE GREAT LAKES/. SHOULD THIS
INDEED BECOME REALIZED...THEN SNOW AMOUNTS COULD BE LOCALLY HIGHER
DOWNWIND FROM THE LAKES.
FURTHER SOUTH AND EAST...WE HAVE OPTED TO KEEP CHARLESTON AND
BEAUFORT COUNTIES OUT OF THE ADVISORY. THE CURRENT THINKING IS
THAT THE BEST FORCING AND MOISTURE WILL REMAIN JUST NW OF BEAUFORT
COUNTY...AND WHILE WE DID CONSIDER INCLUDING CHARLESTON COUNTY IN
THE EARLIER ADVISORY...FOR COORDINATION PURPOSES WITH WFO ILM...WE
HAVE OPTED TO LEAVE THEM OUT AS WELL. THIS COULD CHANGE LATER
TONIGHT AFTER WE GET A BETTER HANDLE ON HOW THIS UNUSUAL SITUATION
WILL EVOLVE.
THE ADVISORY MAY NEED TO BE EXPANDED FURTHER SOUTH AND EAST LATER
TONIGHT OR EARLY TUESDAY...AND THERE IS EVEN THE POTENTIAL FOR AN
UPGRADE TO A WARNING. WHILE WE DO NOT EXPECT TO REACH OUR CRITERIA
OF 2 INCH SNOWFALL IN 12 HOURS...IT COULD BE PRUDENT TO ISSUE THE
WARNING FOR THE IMPACT...GIVEN HOW UNUSUAL THIS SITUATION IS.
MOST OF THE SNOWFALL WILL OCCUR ACROSS GRASSY SURFACES...ROOF TOPS
AND TREES...BUT IF HEAVIER SNOW BANDS DEVELOP...THEN SOME
ROADS...BRIDGES AND OVERPASSES COULD ALSO BECOME COVERED OR AT
LEAST SLICK.
THE SOUTHERN EXTENT OF THE SNOW WILL BE MAINLY THE I-16 CORRIDOR
IN SE GA...WITH THE POSSIBILITY OF FLURRIES EVEN AS FAR SOUTH AS
SAVANNAH...TYBEE ISLAND AND STATESBORO TUESDAY MORNING. SNOW WILL
TAPER OFF FROM SW TO NE DURING THE MID AND LATE AFTERNOON HOURS ON
TUESDAY AS THE ATLC LOW PULLS FURTHER AWAY...AND THE SHORT WAVE
BEGINS ITS EXIT OF THE AREA.
LITTLE CHANGE IN TEMPS ARE EXPECTED ACROSS NORTHERN AREAS ON
TUESDAY...WITH HIGHS GENERALLY IN THE 30S. CENTRAL AREAS WILL
REACH ONLY INTO THE LOWER 40S...WHILE OUR SOUTHERN AREAS WILL BE
THE WARMEST WITH READINGS IN THE MID TO UPPER 40S WHERE THE BEST
INSOLATION WILL OCCUR.
LAKE WINDS...CONTINUED STRONG COLD AIR ADVECTION OVER LAKE
MOULTRIE TUESDAY ACROSS THE WARMER LAKE WATERS WILL RESULT IN
SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS TUESDAY...THUS
A CONTINUATION OF THE LAKE WIND ADVISORY FOR LAKE MOULTRIE.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EXTENDED
PERIOD THIS AFTERNOON...WITH ONLY A FEW MINOR DIFFERENCES NOTED OVER
THE WEEKEND AND INTO EARLY NEXT WEEK.
THE STRONG STORM SYSTEM WILL CONTINUE TO TRACK NORTHEASTWARD AND
AWAY FROM THE AREA TUESDAY NIGHT...WITH HIGH PRESSURE THEN BEGINNING
TO BUILD BACK INTO THE REGION. HAVE MENTIONED A SLIGHT CHANCE OF
FLURRIES IN THE EVENING ACROSS FAR NORTHERN ZONES AS DEEP
MOISTURE...SUFFICIENTLY COLD AIR ALOFT...AND DECENT FETCH OFF OF
LAKE MOULTRIE MAY BE ENOUGH TO KEEP A FEW SNOW FLAKES AROUND. ANY
LINGERING FLURRIES OR LIGHT SNOW SHOWERS SHOULD END IN THE
EVENING...WITH PRECIPITATION FREE WEATHER ANTICIPATED AFTER
MIDNIGHT.
HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA WEDNESDAY THROUGH
FRIDAY...RESULTING IN RAIN FREE WEATHER ACROSS THE REGION.
MODELS ARE IN GOOD AGREEMENT BRINGING A COLD FRONT SLOWLY THROUGH
THE REGION FRIDAY NIGHT THROUGH SATURDAY NIGHT...SO WILL CARRY
SLIGHT CHANCE/LOW CHANCE POPS FOR NOW UNTIL GUIDANCE GETS A BETTER
HANDLE ON TIMING DETAILS. HIGH PRESSURE IS THEN EXPECTED TO BUILD
FROM THE NORTH SUNDAY THROUGH MONDAY...WITH RAIN FREE WEATHER
ANTICIPATED.
&&
.AVIATION /21Z MONDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL PREVAIL TODAY AT BOTH TERMINALS. CLOUD COVER
WILL INCREASE IN COVERAGE THIS AFTERNOON AND EVENING AS A LOW
BEGINS TO DEVELOP TO THE WEST OF THE FORECAST AREA. AS THIS NEW
SYSTEM DEVELOPS...WINDS WILL SHIFT FROM WEST TO SOUTHWEST FOR A
PERIOD BETWEEN 22Z AND 06Z. EXPECT A FEW GUSTS UP TO 17 KNOTS THIS
AFTERNOON AHEAD OF THIS DEVELOPING SYSTEM.
CLOUD COVER WILL CONTINUE TO INCREASE AND CIGS WILL APPROACH MVFR
CONDITIONS BY 09Z AT THE CHS TERMINAL TONIGHT. EXPECT LIGHT RAIN OR
DRIZZLE AT THE CHS TERMINAL TOMORROW MORNING TO TURN OVER TO SNOW
AT DAYBREAK. SNOW ACCUMULATION OF LESS THAN 1/2 INCH IS EXPECTED
AT THIS TIME. WILL KEEP THE SAV TERMINAL DRY FOR THE ENTIRE
FORECAST PERIOD AT THIS TIME. DRY AIR WILL BEGIN TO FILTER INTO THE
REGION BY TOMORROW AFTERNOON AS 12 KT WINDS FROM THE SOUTHWEST
BEGIN TO SHIFT TO THE NORTHWEST. HAVE MAINTAINED MVFR CIGS AT THE
CHS TERMINAL DURING PRECIP ACTIVITY WHILE KEEPING THE SAV
TERMINAL IN VFR CONDITIONS DUE TO THE AMOUNT OF DRY AIR FILTERING
IN ALOFT.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A BRIEF PERIOD OF MVFR
CONDITIONS TUESDAY EVENING AT THE CHARLESTON TERMINAL. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH FRIDAY NIGHT. COULD SEE MVFR
CONDITIONS RETURN SATURDAY AS A COLD FRONT PUSHES INTO THE AREA.
&&
.MARINE...
A TROUGH OF LOW PRESSURE WILL MOVE THROUGH THE WATERS OVERNIGHT...AS
A STORM SYSTEM BEGINS TO ORGANIZE OFF THE CAROLINA COAST. WINDS ARE
EXPECTED TO INCREASE OVER THE COASTAL WATERS AHEAD OF THE
APPROACHING TROUGH OF LOW PRESSURE...AND CONTINUE TO IMPACT THE
MARINE AREA THROUGH TUESDAY EVENING AS STRONG COLD AIR ADVECTION
POURS IN BEHIND THE DEPARTING STORM SYSTEM. HAVE RAISED SMALL CRAFT
ADVISORIES FOR ALL WATERS BEGINNING LATE THIS EVENING OR AFTER
MIDNIGHT...AND CONTINUING THROUGH LATE TUESDAY AFTERNOON OR TUESDAY
EVENING MOST WATERS.
HIGH PRESSURE WILL BUILD BACK INTO THE REGION WEDNESDAY THROUGH
FRIDAY...WITH THE NEXT COLD FRONT EXPECTED TO APPROACH FROM THE WEST
FRIDAY NIGHT AND PUSH THROUGH THE MARINE AREA ON SATURDAY. SEAS MAY
REMAIN IN THE SMALL CRAFT RANGE ACROSS THE OUTER GEORGIA WATERS
EARLY WEDNESDAY...OTHERWISE WINDS AND SEAS ARE EXPECTED TO REMAIN
BELOW HEADLINE THRESHOLDS WEDNESDAY THROUGH SATURDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR SCZ045.
WINTER WEATHER ADVISORY FROM 8 AM TO 10 PM EST TUESDAY FOR
SCZ044-045.
WINTER WEATHER ADVISORY FROM 6 AM TO 5 PM EST TUESDAY FOR
SCZ040-042-043.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 11 PM EST TUESDAY FOR AMZ350-
352.
SMALL CRAFT ADVISORY FROM 1 AM TUESDAY TO 5 AM EST WEDNESDAY
FOR AMZ354.
SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EST
WEDNESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR AMZ330.
&&
$$
33/JRJ
000
FXUS62 KCHS 192156
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
456 PM EST MON JAN 19 2009
...WINTER WEATHER LIKELY IN MANY AREAS TUESDAY...
.SYNOPSIS...
LOW PRES WILL DEVELOP ALONG A COLD FRONT OVER THE ATLC LATE TONIGHT
AND EARLY TUESDAY...THEN SHIFTS NE TO OFF THE MID ATLC COAST DURING
THE AFTERNOON. HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA
TUESDAY NIGHT THROUGH FRIDAY...BEFORE THE NEXT COLD FRONT MOVES
INTO THE REGION OVER THE UPCOMING WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
SHORT WAVE NOW MOVING THROUGH THE TN VALLEY AND THE SOUTHERN
APPALACHIANS WILL PUSH THROUGH THE AREA TONIGHT...BRINGING WITH IT
PLENTY OF CLOUDS EARLY TONIGHT AND A SLIGHT CHANCE OF RAIN.
ALREADY WE ARE SEEING CONSIDERABLE RADAR RETURNS...BUT THEY ARE
STILL JUST LOW TO MID LEVEL CLOUDS WITH THE AIR MASS STILL SO DRY.
DEW POINT DEPRESSIONS ARE 20 DEGREES OR HIGHER AS OF MID
AFTERNOON...THUS IT WILL BE AWHILE BEFORE THINGS MOISTEN UP.
AS THE SHORT WAVES MOVES ACROSS THE AREA TONIGHT IT WILL DEVELOP A
SURFACE LOW PRES SYSTEM OVER CENTRAL AND SOUTHERN SC...WHICH
SHIFTS EAST. THIS LOW WILL DEVELOP FURTHER AS IT REACHES THE
WARMER ATLC WATERS LATE TONIGHT...WITH COLDER AIR TO FUNNEL IN ON
THE BACKSIDE OF THE LOW. STRONG UPWARD OMEGA AND 500-300 MB
Q-VECTOR CONVERGENCE AND INCREASING ISENTROPIC LIFT WILL SUPPORT
SLIGHT CHANCE TO CHANCE POPS MAINLY ACROSS THE CENTRAL AND
NORTHERN CWFA IN CLOSER PROXIMITY TO THE SURFACE LOW. WHILE MOST
OF THE PRECIP TONIGHT WILL BE IN LIQUID FORM...THERE MAY BE A
LITTLE FREEZING PRECIP FAR INLAND LATE AS TEMPS FALL TO NEAR 32
DEGREES. THIS IS MAINLY IN THE AREA FROM SAINT GEORGE TO
WILLIAMS...TO ALLENDALE...HILLTONIA AND MILLEN.
IN ADDITION...SOUNDINGS INDICATE THAT THE COLDER AIR WILL
PENETRATE ENOUGH INTO THE NW ZONES BY MORNING TO ALLOW FOR SOME
LIGHT SNOW TO ALSO MIX IN WITH THE RAIN AND FREEZING RAIN. NO
ACCUMULATION OF ICE OR SNOW WILL OCCUR BY MORNING...BUT MOTORISTS
SHOULD STILL USE EXTREME CARE DUE TO THE WET ROADS...AND KEEP IN
MIND THAT SHOULD TEMPS DROP BELOW FREEZING THAT MINOR ICING WOULD
OCCUR ACROSS SOME OF THE ELEVATED ROAD SURFACE SUCH AS OVERPASSES
AND BRIDGES.
LOW TEMPS FURTHER SE TONIGHT WILL BE IN THE MID AND UPPER 30S...SO
NO CONCERNS FOR WINTER PRECIP ACROSS THE VAST MAJORITY OF THE
FORECAST AREA.
LAKE WINDS...STRONG COLD AIR ADVECTION WILL BEGIN OVER LAKE
MOULTRIE LATE TONIGHT AS A TROUGH OF LOW PRESSURE MOVES THROUGH
THE AREA AND A STRONG STORM SYSTEM BEGINS TO ORGANIZE OFF THE
CAROLINA COAST. SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS
ARE EXPECTED LATE TONIGHT...THEREFORE WILL ISSUE A LAKE WIND
ADVISORY FOR LAKE MOULTRIE.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
WE HAVE INITIATED A WINTER WEATHER ADVISORY FOR SNOW ACROSS OUR
INLAND SC COUNTIES STARTING TUESDAY MORNING. AT THIS TIME HOWEVER
THAT DOES NOT INCLUDE CHARLESTON OR BEAUFORT COUNTIES...BUT THIS
COULD CHANGE DEPENDING UPON THE EVOLUTION OF THE SURFACE LOW AS IT
REACHES THE ATLC AND THE STRENGTH OF THE UPPER SHORT WAVE AND
ASSOCIATED DYNAMICS.
THE SURFACE LOW WILL STRENGTHEN AS IT MOVES ACROSS THE GULF STREAM
WATERS TUESDAY MORNING...WITH A CONTINUED INFLUX OF COLD AIR
MOVING IN FROM THE NW IN ITS WAKE. INDICATIONS ARE THAT ANY LIGHT
RAINS AND/OR MIXED PRECIP IN THE MORNING WILL CHANGE OVER TO ALL
SNOW BY AFTERNOON...AS THICKNESS...CROSS-SECTIONS...SOUNDINGS AND
WET BULBS ALL SUPPORT FROZEN PRECIP OVERSPREADING THE AREA.
AT 12Z...CONDITIONS OVERALL ARE TOO WARM AND TOO DRY TO SUPPORT
ANYTHING MORE THAN A LITTLE LIGHT RAIN...SNOW AND/OR FREEZING RAIN.
FROM 15Z TO 21Z...THE COLDER AIR IS OVERSPREADING THE AREA...WITH
A GRADUAL INCREASE IN MOISTURE. WHILE THE -10 TO -20C ICE GROWTH
ZONE HAS MOSTLY LESS THAN 80 PERCENT RH EARLY IN THIS TIME
PERIOD...IT DOES INCREASE TO AROUND 80 PERCENT OVER NORTHERN AND
WESTERN AREA BY AFTERNOON. SIGNIFICANT QG FORCING AT BOTH 700-500
MB AND 500-300 MB IS OCCURRING...WITH WEAK TO MODERATE LOW-MID
FRONTOGENESIS. ALSO...A 500-300 MB JET MOVES ACROSS THE AREA
DURING THE MORNING AND EARLY AFTERNOON. CROSS-SECTIONS ALSO SHOW
POSSIBLE BANDING OF SNOW DURING THIS TIME...WITH SATURATED EPV
ALONG WITH THE FRONTOGENESIS. THIS IS FURTHER SUPPORTED BY THE
ISENTROPIC TROWEL ANALYSIS WHICH SHOWS WEAK ISENTROPIC LIFT AT THE
290 AND 295K SURFACES DURING TUESDAY AFTERNOON...IN SYNC WITH THE
UPWARD OMEGA FIELDS.
GARCIA TECHNIQUE YIELDS ABOUT 1/2 TO 1 INCH OF SNOWFALL ACROSS
BEREKLEY...DORCHESTER...INLAND COLLETON...HAMPTON AND ALLENDALE
COUNTIES. HOWEVER...THE GROUND IS RELATIVELY WARM...WITH RECENT
SOIL TEMP AT KCHS STILL NEAR 50 DEGREES. WHILE THIS MIGHT POINT TO
SLIGHTLY LESS AMOUNTS...GIVEN THE POTENTIAL FOR HEAVIER BURSTS OF
SNOW WITH POSSIBLE CONVECTIVE BANDING...AND DECREASE IN SNOW
AMOUNTS DUE TO THE WARM GROUND SHOULD BE COMPENSATED FOR BY THE
POSSIBLE HEAVIER SNOWFALL. IN ADDITION...THE NW FETCH IS OFF LAKE
MOULTRIE AND LAKE MARION...OR FROM ABOUT 300-310 DEGREES.
TEMPERATURE DIFFERENCE BETWEEN THE AIR AND THE LAKE WILL BE ABOUT
10-12 DEGREES...WHICH LOOKS TO BE ENOUGH TO ALLOW FOR THE
POSSIBILITY OF A BAND OF SNOW DEVELOPING OVER THE LAKE WATERS
/SIMILAR TO LAKE EFFECT SNOWS IN THE GREAT LAKES/. SHOULD THIS
INDEED BECOME REALIZED...THEN SNOW AMOUNTS COULD BE LOCALLY HIGHER
DOWNWIND FROM THE LAKES.
FURTHER SOUTH AND EAST...WE HAVE OPTED TO KEEP CHARLESTON AND
BEAUFORT COUNTIES OUT OF THE ADVISORY. THE CURRENT THINKING IS
THAT THE BEST FORCING AND MOISTURE WILL REMAIN JUST NW OF BEAUFORT
COUNTY...AND WHILE WE DID CONSIDER INCLUDING CHARLESTON COUNTY IN
THE EARLIER ADVISORY...FOR COORDINATION PURPOSES WITH WFO ILM...WE
HAVE OPTED TO LEAVE THEM OUT AS WELL. THIS COULD CHANGE LATER
TONIGHT AFTER WE GET A BETTER HANDLE ON HOW THIS UNUSUAL SITUATION
WILL EVOLVE.
THE ADVISORY MAY NEED TO BE EXPANDED FURTHER SOUTH AND EAST LATER
TONIGHT OR EARLY TUESDAY...AND THERE IS EVEN THE POTENTIAL FOR AN
UPGRADE TO A WARNING. WHILE WE DO NOT EXPECT TO REACH OUR CRITERIA
OF 2 INCH SNOWFALL IN 12 HOURS...IT COULD BE PRUDENT TO ISSUE THE
WARNING FOR THE IMPACT...GIVEN HOW UNUSUAL THIS SITUATION IS.
MOST OF THE SNOWFALL WILL OCCUR ACROSS GRASSY SURFACES...ROOF TOPS
AND TREES...BUT IF HEAVIER SNOW BANDS DEVELOP...THEN SOME
ROADS...BRIDGES AND OVERPASSES COULD ALSO BECOME COVERED OR AT
LEAST SLICK.
THE SOUTHERN EXTENT OF THE SNOW WILL BE MAINLY THE I-16 CORRIDOR
IN SE GA...WITH THE POSSIBILITY OF FLURRIES EVEN AS FAR SOUTH AS
SAVANNAH...TYBEE ISLAND AND STATESBORO TUESDAY MORNING. SNOW WILL
TAPER OFF FROM SW TO NE DURING THE MID AND LATE AFTERNOON HOURS ON
TUESDAY AS THE ATLC LOW PULLS FURTHER AWAY...AND THE SHORT WAVE
BEGINS ITS EXIT OF THE AREA.
LITTLE CHANGE IN TEMPS ARE EXPECTED ACROSS NORTHERN AREAS ON
TUESDAY...WITH HIGHS GENERALLY IN THE 30S. CENTRAL AREAS WILL
REACH ONLY INTO THE LOWER 40S...WHILE OUR SOUTHERN AREAS WILL BE
THE WARMEST WITH READINGS IN THE MID TO UPPER 40S WHERE THE BEST
INSOLATION WILL OCCUR.
LAKE WINDS...CONTINUED STRONG COLD AIR ADVECTION OVER LAKE
MOULTRIE TUESDAY ACROSS THE WARMER LAKE WATERS WILL RESULT IN
SUSTAINED WINDS OF 20 KNOTS WITH GUSTS TO 25 KNOTS TUESDAY...THUS
A CONTINUATION OF THE LAKE WIND ADVISORY FOR LAKE MOULTRIE.
&&
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
MEDIUM RANGE GUIDANCE IS IN GOOD AGREEMENT THROUGH THE EXTENDED
PERIOD THIS AFTERNOON...WITH ONLY A FEW MINOR DIFFERENCES NOTED OVER
THE WEEKEND AND INTO EARLY NEXT WEEK.
THE STRONG STORM SYSTEM WILL CONTINUE TO TRACK NORTHEASTWARD AND
AWAY FROM THE AREA TUESDAY NIGHT...WITH HIGH PRESSURE THEN BEGINNING
TO BUILD BACK INTO THE REGION. HAVE MENTIONED A SLIGHT CHANCE OF
FLURRIES IN THE EVENING ACROSS FAR NORTHERN ZONES AS DEEP
MOISTURE...SUFFICIENTLY COLD AIR ALOFT...AND DECENT FETCH OFF OF
LAKE MOULTRIE MAY BE ENOUGH TO KEEP A FEW SNOW FLAKES AROUND. ANY
LINGERING FLURRIES OR LIGHT SNOW SHOWERS SHOULD END IN THE
EVENING...WITH PRECIPITATION FREE WEATHER ANTICIPATED AFTER
MIDNIGHT.
HIGH PRESSURE WILL THEN BUILD BACK INTO THE AREA WEDNESDAY THROUGH
FRIDAY...RESULTING IN RAIN FREE WEATHER ACROSS THE REGION.
MODELS ARE IN GOOD AGREEMENT BRINGING A COLD FRONT SLOWLY THROUGH
THE REGION FRIDAY NIGHT THROUGH SATURDAY NIGHT...SO WILL CARRY
SLIGHT CHANCE/LOW CHANCE POPS FOR NOW UNTIL GUIDANCE GETS A BETTER
HANDLE ON TIMING DETAILS. HIGH PRESSURE IS THEN EXPECTED TO BUILD
FROM THE NORTH SUNDAY THROUGH MONDAY...WITH RAIN FREE WEATHER
ANTICIPATED.
&&
.AVIATION /21Z MONDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL PREVAIL TODAY AT BOTH TERMINALS. CLOUD COVER
WILL INCREASE IN COVERAGE THIS AFTERNOON AND EVENING AS A LOW
BEGINS TO DEVELOP TO THE WEST OF THE FORECAST AREA. AS THIS NEW
SYSTEM DEVELOPS...WINDS WILL SHIFT FROM WEST TO SOUTHWEST FOR A
PERIOD BETWEEN 22Z AND 06Z. EXPECT A FEW GUSTS UP TO 17 KNOTS THIS
AFTERNOON AHEAD OF THIS DEVELOPING SYSTEM.
CLOUD COVER WILL CONTINUE TO INCREASE AND CIGS WILL APPROACH MVFR
CONDITIONS BY 09Z AT THE CHS TERMINAL TONIGHT. EXPECT LIGHT RAIN OR
DRIZZLE AT THE CHS TERMINAL TOMORROW MORNING TO TURN OVER TO SNOW
AT DAYBREAK. SNOW ACCUMULATION OF LESS THAN 1/2 INCH IS EXPECTED
AT THIS TIME. WILL KEEP THE SAV TERMINAL DRY FOR THE ENTIRE
FORECAST PERIOD AT THIS TIME. DRY AIR WILL BEGIN TO FILTER INTO THE
REGION BY TOMORROW AFTERNOON AS 12 KT WINDS FROM THE SOUTHWEST
BEGIN TO SHIFT TO THE NORTHWEST. HAVE MAINTAINED MVFR CIGS AT THE
CHS TERMINAL DURING PRECIP ACTIVITY WHILE KEEPING THE SAV
TERMINAL IN VFR CONDITIONS DUE TO THE AMOUNT OF DRY AIR FILTERING
IN ALOFT.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A BRIEF PERIOD OF MVFR
CONDITIONS TUESDAY EVENING AT THE CHARLESTON TERMINAL. OTHERWISE VFR
CONDITIONS ARE EXPECTED THROUGH FRIDAY NIGHT. COULD SEE MVFR
CONDITIONS RETURN SATURDAY AS A COLD FRONT PUSHES INTO THE AREA.
&&
.MARINE...
A TROUGH OF LOW PRESSURE WILL MOVE THROUGH THE WATERS OVERNIGHT...AS
A STORM SYSTEM BEGINS TO ORGANIZE OFF THE CAROLINA COAST. WINDS ARE
EXPECTED TO INCREASE OVER THE COASTAL WATERS AHEAD OF THE
APPROACHING TROUGH OF LOW PRESSURE...AND CONTINUE TO IMPACT THE
MARINE AREA THROUGH TUESDAY EVENING AS STRONG COLD AIR ADVECTION
POURS IN BEHIND THE DEPARTING STORM SYSTEM. HAVE RAISED SMALL CRAFT
ADVISORIES FOR ALL WATERS BEGINNING LATE THIS EVENING OR AFTER
MIDNIGHT...AND CONTINUING THROUGH LATE TUESDAY AFTERNOON OR TUESDAY
EVENING MOST WATERS.
HIGH PRESSURE WILL BUILD BACK INTO THE REGION WEDNESDAY THROUGH
FRIDAY...WITH THE NEXT COLD FRONT EXPECTED TO APPROACH FROM THE WEST
FRIDAY NIGHT AND PUSH THROUGH THE MARINE AREA ON SATURDAY. SEAS MAY
REMAIN IN THE SMALL CRAFT RANGE ACROSS THE OUTER GEORGIA WATERS
EARLY WEDNESDAY...OTHERWISE WINDS AND SEAS ARE EXPECTED TO REMAIN
BELOW HEADLINE THRESHOLDS WEDNESDAY THROUGH SATURDAY.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...LAKE WIND ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR SCZ045.
WINTER WEATHER ADVISORY FROM 8 AM TO 10 PM EST TUESDAY FOR
SCZ044-045.
WINTER WEATHER ADVISORY FROM 6 AM TO 5 PM EST TUESDAY FOR
SCZ040-042-043.
MARINE...SMALL CRAFT ADVISORY FROM 1 AM TO 11 PM EST TUESDAY FOR AMZ350-
352.
SMALL CRAFT ADVISORY FROM 1 AM TUESDAY TO 5 AM EST WEDNESDAY
FOR AMZ354.
SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EST
WEDNESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 AM TO 5 PM EST TUESDAY FOR AMZ330.
&&
$$
33/JRJ
000
FXUS62 KCHS 191754
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1254 PM EST MON JAN 19 2009
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP ALONG A DESCENDING COLD FRONT EARLY
TUESDAY AND PULL NORTHEAST OFF THE CAROLINA COAST BY TUESDAY
AFTERNOON. HIGH PRESSURE WILL THEN BUILD INTO THE AREA THROUGH
FRIDAY...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
SHORT WAVE MOVING THROUGH THE TN VALLEY THIS MORNING WILL PUSH
TOWARD THE AREA THIS AFTERNOON...RESULTING IN AN INCREASE IN MID
AND HIGH LEVEL CLOUDINESS. THAT CLOUD COVER IS NOW MOVING INTO
UPSTATE SC AND WESTERN AND CENTRAL GA...AND WILL STEADILY PUSH NE
AND EAST THROUGH THE AFTERNOON. THUS OUR PARTLY CLOUDY OR MOSTLY
CLEAR CONDITIONS FROM THIS MORNING WILL BECOME MOSTLY CLOUDY
ACROSS THE MAJORITY OF THE FORECAST AREA THIS AFTERNOON. THE
EXCEPTION WILL BE THE FAR SE CORNER...WHERE NO WORSE THAN PARTLY
CLOUDY SKY CONDITION WILL OCCUR.
SHORT WAVE WILL ALSO CAUSE AN INCREASE IN MOISTURE AS IT
APPROACHES...AND WE WILL SEE A FEW RETURNS ON RADAR LATE...BUT
BELIEVE IT WOULD REMAIN AS VIRGA GIVEN LARGE DEW POINT
DEPRESSIONS. OUR GRIDS WILL SHOW POPS NO HIGHER THAN 10-12 PERCENT
OVER THE NW TIER...BUT NO MENTION OF PRECIP TODAY IN THE PUBLIC
FORECAST.
REGARDING TEMPS...1000-850 THICKNESS SCHEME SUPPORTS MID 50S NW
TO LOWER 60S SE. WE WILL TRIM TEMPS OVER NW ZONES A DEGREE OR TWO
TO ACCOUNT FOR MORE CLOUD COVER WHICH WILL HOLD TEMPS DOWN IN THE
LOWER 50S...BUT OTHERWISE THICKNESS FORECASTS WILL BE REALIZED.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
ANOTHER IN A SERIES OF SHORTWAVE TROUGHS WILL ROUND THE BASE OF
THE AMPLIFYING LONG-WAVE TROUGH TONIGHT. THE NAM/GFS AND ECMWF
HAS FINALLY COME INTO SOME SORT OF AGREEMENT THAT THE APPROACHING
SHORTWAVE WILL INITIATE CYCLOGENESIS ACROSS THE MIDLANDS THIS
EVENING WITH THE DEVELOPING LOW REFORMING OFF THE NORTHEAST SOUTH
CAROLINA COAST BY SUNRISE TUESDAY WHERE LOW-LEVEL BAROCLINICITY
IS THE GREATEST. STRONG UPWARD FORCING AHEAD OF THE SHORTWAVE INDUCED
BY IMPRESSIVE 500-300MB Q-VECTOR CONVERGENCE AND INCREASING
ISENTROPIC ASSENT WILL LIKELY SUPPORT AT LEAST PATCHY PRECIPITATION
AFTER MIDNIGHT WITH THE PRECIPITATION INCREASING IN BOTH COVERAGE
AND INTENSITY AS SUNRISE APPROACHES. WITH TEMPERATURES FALLING INTO
THE 30S AND TEMPERATURES ABOVE THE BOUNDARY LAYER PROGGED TO DROPPED
BELOW FREEZING...SOME P-TYPE PROBLEMS APPEAR LIKELY WELL INLAND FROM
THE COAST.
MODEL AND BUFKIT SOUNDINGS SUGGEST THAT ALTHOUGH THE LOWER
TROPOSPHERE WILL SUFFICIENTLY MOISTEN TO SUPPORT PRECIPITATION
THROUGH THE NIGHT...THE ATMOSPHERE LOOKS ONLY MARGINALLY FAVORABLE
TO SUPPORT ICE FORMATION WITHIN THE FAVORABLE -10 TO -20C
DENDRITIC GROWTH ZONE. THIS TYPE OF THERMAL SETUP WOULD TYPICALLY
YIELD A MIXTURE OF RAIN AND SLEET BUT GIVEN THE STRENGTH OF Q-C
FORCING WE BELIEVE ANY RAIN WILL MIX WITH OR CHANGE TO SNOW LATE IN
THE NIGHT WELL INLAND FROM THE COAST. IN FACT...CRITICAL LOW-LEVEL
THICKNESSES SUPPORT A CHANGE OVER TO ALL SNOW ACROSS THE ENTIRE
FORECAST AREA AFTER 10Z AS THE BAND OF STRONGEST UPPER FORCING AND
ASSOCIATED DYNAMIC COOLING MOVE IN FROM THE WEST. PLAN TO BE FAIRLY
CONSERVATIVE WITH POPS TONIGHT GOING NO HIGHER THAN 20-30 PERCENT.
WILL SHOW RAIN SHOWERS CHANGING TO SNOW IN A CORRIDOR FROM ALLENDALE
EAST TO NORTHERN COLLETON WITH THE RAIN BECOMING MIXED WITH SNOW
ACROSS DORCHESTER AND BERKELEY. THERE MAY EVEN BE A SMALL CORRIDOR
OF FREEZING RAIN FROM NORTHERN PORTIONS OF EFFINGHAM AND INLAND
JASPER IF TEMPERATURES CAN DROP TO FREEZING WITH RAIN EXPECTED
ELSEWHERE. EXPECT LITTLE OR NO ICE/SLEET/SNOW ACCUMULATIONS
THROUGH SUNRISE SO NO ADVISORIES...WATCHES OR WARNINGS ARE PLANNED
AT THIS TIME FOR THIS TIME PERIOD.
LOWS WILL RANGE FROM THE UPPER 20S TO AROUND 30 ACROSS FAR
INTERIOR SOUTHEAST GEORGIA TO THE MID 30S ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS ARE IN FAIRLY GOOD AGREEMENT INDICATING WRAP AROUND PRECIP
AFFECTING AREAS MAINLY NORTH OF INTERSTATE 16 EARLY TUESDAY
MORNING...AS LOW PRESSURE OFF THE CAROLINA COAST DEEPENS AND SHIFTS
NORTHEAST. COLD AIR WILL ADVECT INTO THE REGION ON THE BACK SIDE
OF THE COASTAL LOW...AND TEMPERATURES WILL REMAIN IN THE LOWER 30S
FOR THE FIRST FEW HOURS AFTER SUNRISE. CONSIDERING THE STRONG UPPER
LEVEL DYNAMICS DUE TO AN AMPLIFIED UPPER TROUGH AND PLENTY OF VORT
ENERGY...SNOW SHOWERS ARE POSSIBLE WITHIN THE COLD AIR MASS
TUESDAY MORNING. PRECIP CHANCES WILL DIMINISH TUESDAY
AFTERNOON...HOWEVER ANY LIGHT SHOWERS WILL LIKELY BE MIXED WITH
SNOW. SREF SNOW PROBABILITIES ARE UP TO 40 PERCENT TUESDAY...WITH
GFS AND NAM BOTH INDICATING 12 HOUR SNOW ACCUMULATIONS POTENTIALLY
UP TO 0.5 INCH IN THE FAR INLAND SECTIONS FROM BERKELEY COUNTY
SOUTHWEST TO ALLENDALE COUNTY.
HAVE INDICATED A SOLID CHANCE OF SNOW SHOWERS FOR ALL OF THE SOUTH
CAROLINA ZONES TUESDAY MORNING...WITH PRECIP CHANCES DIMINISHING
TO THE SOUTH. AFTER 15Z...MENTION RAIN SHOWERS MIXED WITH SNOW
SHOWERS...THEN RAIN/SNOW CHANCES DROPPING TO AROUND 20 PERCENT
AFTER 18Z. UPON COLLABORATION WITH HPC AND SURROUNDING OFFICES...
HAVE OPTED TO HOLD OFF ON ANY WATCHES OR ADVISORIES AT THIS POINT.
HOWEVER...A WINTER WEATHER ADVISORY OR WINTER STORM WATCH/WARNING
MAY BE ISSUED BY SUBSEQUENT SHIFTS AS THE EVENT APPROACHES.
TEMPERATURES WILL BE SUPPRESSED IN THE LOWER 40S ON TUESDAY...WITH
OVERNIGHT LOWS DROPPING INTO THE 20S. CONSIDERING THE
PRECIPITATION OCCURRING DURING THE DAY...ICE FORMATION ON ROADS
TUESDAY NIGHT COULD BE A HAZARD. WIND CHILLS COULD ALSO POSE A
PROBLEM WITH VALUES DROPPING TO 10-15 DEGREES INLAND AND 15-20
DEGREES AT THE COAST.
SURFACE HIGH PRESSURE WILL BUILD IN FROM THE GULF OF MEXICO BY
WEDNESDAY...RESULTING IN RAIN FREE CONDITIONS AND A WARMING TREND
THROUGH FRIDAY. HIGH TEMPERATURES WILL REACH SEASONAL NORMALS IN
THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY. SOUTHERLY FLOW
WITHIN THE WARM SECTOR OF ANOTHER APPROACHING COLD FRONT WILL
ALLOW TEMPERATURES ON FRIDAY AND SATURDAY TO RISE ABOVE
NORMALS...IN THE MID TO UPPER 60S.
INTRODUCE A SLIGHT CHANCE OF RAIN ON SATURDAY AS THE COLD FRONT
DROPS INTO THE REGION FROM THE NORTHWEST. DUE TO SOME TIMING
ISSUES BETWEEN THE GFS AND ECMWF...HAVE MAINTAINED 20 PERCENT POPS
THROUGH THE WEEKEND.
&&
.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR CONDITIONS WILL PREVAIL TODAY AT BOTH TERMINALS. CLOUD COVER
WILL INCREASE IN COVERAGE THIS AFTERNOON AND EVENING AS A LOW
BEGINS TO DEVELOP TO THE WEST OF THE FORECAST AREA. AS THIS NEW
SYSTEM DEVELOPS...WINDS WILL SHIFT FROM WEST TO SOUTHWEST FOR A
PERIOD BETWEEN 22Z AND 06Z. EXPECT A FEW GUSTS UP TO 17 KNOTS THIS
AFTERNOON AHEAD OF THIS DEVELOPING SYSTEM.
CLOUD COVER WILL CONTINUE TO INCREASE AND CIGS WILL APPROACH MVFR
CONDITIONS BY 09Z AT THE CHS TERMINAL TONIGHT. EXPECT LIGHT RAIN OR
DRIZZLE AT THE CHS TERMINAL TOMORROW MORNING TO TURN OVER TO SNOW
AT DAYBREAK. SNOW ACCUMULATION OF LESS THAN 1/2 INCH IS EXPECTED
AT THIS TIME. WILL KEEP THE SAV TERMINAL DRY FOR THE ENTIRE
FORECAST PERIOD AT THIS TIME. DRY AIR WILL BEGIN TO FILTER INTO THE
REGION BY TOMORROW AFTERNOON AS 12 KT WINDS FROM THE SOUTHWEST
BEGIN TO SHIFT TO THE NORTHWEST. HAVE MAINTAINED MVFR CIGS AT THE
CHS TERMINAL DURING PRECIP ACTIVITY WHILE KEEPING THE SAV
TERMINAL IN VFR CONDITIONS DUE TO THE AMOUNT OF DRY AIR FILTERING
IN ALOFT.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MVFR
CONDITIONS TUESDAY EVENING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER
WILL PREVAIL THROUGH THE PERIOD.
&&
.MARINE...
A TROUGH OF LOW PRESSURE WILL APPROACH FROM THE WEST TODAY...THEN
PUSH THROUGH THE WATERS LATE TONIGHT AS A STORM SYSTEM BEGINS TO
ORGANIZE OFF THE CAROLINA COAST. HAVE MADE SOME MINOR TWEAKS TO
THE COASTAL WATERS FORECAST...MAINLY TO REMOVE MORNING WORDING.
HAVE ALSO PUSHED THE SMALL CRAFT ADVISORY BACK ACROSS THE OUTER
GEORGIA WATERS AS WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW
HEADLINE THRESHOLDS INTO THE EVENING.
SOUTHWEST WINDS WILL INCREASE TONIGHT AS A LOW-LEVEL JET MOVES
ACROSS THE WATERS. MIXING PROFILES WILL REMAIN LESS THAN IDEAL
ACROSS THE COOLER NEARSHORE WATERS SO WINDS WILL BE CAPPED AT 15-20
KT FOR NOW. WARMER CONDITIONS OVER THE GEORGIA OFFSHORE WATERS WILL
SUPPORT 20-25 KT.
TUESDAY THROUGH FRIDAY...COLD AIR ADVECTION AND A TIGHT PRESSURE
GRADIENT ON THE BACK SIDE OF A DEEPENING COASTAL LOW WILL MAINTAIN
STRONG WEST WINDS OVER THE MARINE ZONES TUESDAY. SMALL CRAFT
ADVISORY CONDITIONS WILL LIKELY BE REACHED FOR MOST OF THE COASTAL
WATERS...PERHAPS INCLUDING THE CHARLESTON HARBOR. WILL NEED TO
CLOSELY MONITOR MODEL TRENDS FOR POTENTIAL MARGINAL GALE FORCE
WINDS IN THE OUTER GEORGIA WATERS. AT THIS POINT...HAVE INDICATED
25 TO 30 KT WINDS FOR THE OFFSHORE GEORGIA ZONES WITH POSSIBLE
OCCASIONAL GALE FORCE GUSTS. FEEL THAT SEAS WILL BE 5 TO 7 FT IN
THE OUTER WATERS...MITIGATED SOMEWHAT BY THE OFFSHORE FLOW.
THE COASTAL LOW WILL QUICKLY DEPART TO THE NORTHEAST TUESDAY
AFTERNOON/EVENING...WITH HIGH PRESSURE BUILDING IN FROM THE GULF OF
MEXICO. EXPECT A GRADUAL DECREASE IN WEST WINDS WEDNESDAY...BECOMING
SOUTHWEST AS THE SURFACE HIGH SHIFTS OFF THE FLORIDA COAST LATE IN
THE WEEK.
A COLD FRONT WILL APPROACH FROM THE NORTHWEST OVER THE WEEKEND...BUT
THERE REMAINS A LOT OF UNCERTAINTY REGARDING TIMING AND STRENGTH
OF THE FEATURE.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EST
WEDNESDAY FOR AMZ374.
&&
$$
000
FXUS62 KCHS 191606
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1106 AM EST MON JAN 19 2009
...WINTER WEATHER POSSIBLE LATE TONIGHT AND TUESDAY...
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP ALONG A DESCENDING COLD FRONT EARLY
TUESDAY AND PULL NORTHEAST OFF THE CAROLINA COAST BY TUESDAY
AFTERNOON. HIGH PRESSURE WILL THEN BUILD INTO THE AREA THROUGH
FRIDAY...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
STILL SOME PATCHY DENSE FOG ALONG THE COAST FROM EDISTO ISLAND NORTH
TO ISLE OF PALMS AND CAPERS ISLAND...AS WELL AS ACROSS NORTHERN
DORCHESTER AND COLLETON COUNTIES. HOWEVER...FOG WILL BURN OFF BY
LATE MORNING AND WE WILL REMOVE MENTION FROM THE FORECAST.
OTHERWISE...SHORT WAVE MOVING THROUGH THE TN VALLEY THIS MORNING
WILL PUSH TOWARD THE AREA THIS AFTERNOON...RESULTING IN AN
INCREASE IN MID AND HIGH LEVEL CLOUDINESS. THAT CLOUD COVER IS NOW
MOVING INTO UPSTATE SC AND WESTERN AND CENTRAL GA...AND WILL
STEADILY PUSH NE AND EAST THROUGH THE AFTERNOON. THUS OUR PARTLY
CLOUDY OR MOSTLY CLEAR CONDITIONS FROM THIS MORNING WILL BECOME
MOSTLY CLOUDY ACROSS THE MAJORITY OF THE FORECAST AREA THIS
AFTERNOON. THE EXCEPTION WILL BE THE FAR SE CORNER...WHERE NO
WORSE THAN PARTLY CLOUDY SKY CONDITION WILL OCCUR.
SHORT WAVE WILL ALSO CAUSE AN INCREASE IN MOISTURE AS IT
APPROACHES...AND WE WILL SEE A FEW RETURNS ON RADAR LATE...BUT
BELIEVE IT WOULD REMAIN AS VIRGA GIVEN LARGE DEW POINT
DEPRESSIONS. OUR GRIDS WILL SHOW POPS NO HIGHER THAN 10-12 PERCENT
OVER THE NW TIER...BUT NO MENTION OF PRECIP TODAY IN THE PUBLIC
FORECAST.
REGARDING TEMPS...1000-850 THICKNESS SCHEME SUPPORTS MID 50S NW
TO LOWER 60S SE. WE WILL TRIM TEMPS OVER NW ZONES A DEGREE OR TWO
TO ACCOUNT FOR MORE CLOUD COVER WHICH WILL HOLD TEMPS DOWN IN THE
LOWER 50S...BUT OTHERWISE THICKNESS FORECASTS WILL BE REALIZED.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
ANOTHER IN A SERIES OF SHORTWAVE TROUGHS WILL ROUND THE BASE OF
THE AMPLIFYING LONG-WAVE TROUGH TONIGHT. THE NAM/GFS AND ECMWF
HAS FINALLY COME INTO SOME SORT OF AGREEMENT THAT THE APPROACHING
SHORTWAVE WILL INITIATE CYCLOGENESIS ACROSS THE MIDLANDS THIS
EVENING WITH THE DEVELOPING LOW REFORMING OFF THE NORTHEAST SOUTH
CAROLINA COAST BY SUNRISE TUESDAY WHERE LOW-LEVEL BAROCLINICITY
IS THE GREATEST. STRONG UPWARD FORCING AHEAD OF THE SHORTWAVE INDUCED
BY IMPRESSIVE 500-300MB Q-VECTOR CONVERGENCE AND INCREASING
ISENTROPIC ASSENT WILL LIKELY SUPPORT AT LEAST PATCHY PRECIPITATION
AFTER MIDNIGHT WITH THE PRECIPITATION INCREASING IN BOTH COVERAGE
AND INTENSITY AS SUNRISE APPROACHES. WITH TEMPERATURES FALLING INTO
THE 30S AND TEMPERATURES ABOVE THE BOUNDARY LAYER PROGGED TO DROPPED
BELOW FREEZING...SOME P-TYPE PROBLEMS APPEAR LIKELY WELL INLAND FROM
THE COAST.
MODEL AND BUFKIT SOUNDINGS SUGGEST THAT ALTHOUGH THE LOWER
TROPOSPHERE WILL SUFFICIENTLY MOISTEN TO SUPPORT PRECIPITATION
THROUGH THE NIGHT...THE ATMOSPHERE LOOKS ONLY MARGINALLY FAVORABLE
TO SUPPORT ICE FORMATION WITHIN THE FAVORABLE -10 TO -20C
DENDRITIC GROWTH ZONE. THIS TYPE OF THERMAL SETUP WOULD TYPICALLY
YIELD A MIXTURE OF RAIN AND SLEET BUT GIVEN THE STRENGTH OF Q-C
FORCING WE BELIEVE ANY RAIN WILL MIX WITH OR CHANGE TO SNOW LATE IN
THE NIGHT WELL INLAND FROM THE COAST. IN FACT...CRITICAL LOW-LEVEL
THICKNESSES SUPPORT A CHANGE OVER TO ALL SNOW ACROSS THE ENTIRE
FORECAST AREA AFTER 10Z AS THE BAND OF STRONGEST UPPER FORCING AND
ASSOCIATED DYNAMIC COOLING MOVE IN FROM THE WEST. PLAN TO BE FAIRLY
CONSERVATIVE WITH POPS TONIGHT GOING NO HIGHER THAN 20-30 PERCENT.
WILL SHOW RAIN SHOWERS CHANGING TO SNOW IN A CORRIDOR FROM ALLENDALE
EAST TO NORTHERN COLLETON WITH THE RAIN BECOMING MIXED WITH SNOW
ACROSS DORCHESTER AND BERKELEY. THERE MAY EVEN BE A SMALL CORRIDOR
OF FREEZING RAIN FROM NORTHERN PORTIONS OF EFFINGHAM AND INLAND
JASPER IF TEMPERATURES CAN DROP TO FREEZING WITH RAIN EXPECTED
ELSEWHERE. EXPECT LITTLE OR NO ICE/SLEET/SNOW ACCUMULATIONS
THROUGH SUNRISE SO NO ADVISORIES...WATCHES OR WARNINGS ARE PLANNED
AT THIS TIME FOR THIS TIME PERIOD.
LOWS WILL RANGE FROM THE UPPER 20S TO AROUND 30 ACROSS FAR
INTERIOR SOUTHEAST GEORGIA TO THE MID 30S ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS ARE IN FAIRLY GOOD AGREEMENT INDICATING WRAP AROUND PRECIP
AFFECTING AREAS MAINLY NORTH OF INTERSTATE 16 EARLY TUESDAY
MORNING...AS LOW PRESSURE OFF THE CAROLINA COAST DEEPENS AND SHIFTS
NORTHEAST. COLD AIR WILL ADVECT INTO THE REGION ON THE BACK SIDE
OF THE COASTAL LOW...AND TEMPERATURES WILL REMAIN IN THE LOWER 30S
FOR THE FIRST FEW HOURS AFTER SUNRISE. CONSIDERING THE STRONG UPPER
LEVEL DYNAMICS DUE TO AN AMPLIFIED UPPER TROUGH AND PLENTY OF VORT
ENERGY...SNOW SHOWERS ARE POSSIBLE WITHIN THE COLD AIR MASS
TUESDAY MORNING. PRECIP CHANCES WILL DIMINISH TUESDAY
AFTERNOON...HOWEVER ANY LIGHT SHOWERS WILL LIKELY BE MIXED WITH
SNOW. SREF SNOW PROBABILITIES ARE UP TO 40 PERCENT TUESDAY...WITH
GFS AND NAM BOTH INDICATING 12 HOUR SNOW ACCUMULATIONS POTENTIALLY
UP TO 0.5 INCH IN THE FAR INLAND SECTIONS FROM BERKELEY COUNTY
SOUTHWEST TO ALLENDALE COUNTY.
HAVE INDICATED A SOLID CHANCE OF SNOW SHOWERS FOR ALL OF THE SOUTH
CAROLINA ZONES TUESDAY MORNING...WITH PRECIP CHANCES DIMINISHING
TO THE SOUTH. AFTER 15Z...MENTION RAIN SHOWERS MIXED WITH SNOW
SHOWERS...THEN RAIN/SNOW CHANCES DROPPING TO AROUND 20 PERCENT
AFTER 18Z. UPON COLLABORATION WITH HPC AND SURROUNDING OFFICES...
HAVE OPTED TO HOLD OFF ON ANY WATCHES OR ADVISORIES AT THIS POINT.
HOWEVER...A WINTER WEATHER ADVISORY OR WINTER STORM WATCH/WARNING
MAY BE ISSUED BY SUBSEQUENT SHIFTS AS THE EVENT APPROACHES.
TEMPERATURES WILL BE SUPPRESSED IN THE LOWER 40S ON TUESDAY...WITH
OVERNIGHT LOWS DROPPING INTO THE 20S. CONSIDERING THE
PRECIPITATION OCCURRING DURING THE DAY...ICE FORMATION ON ROADS
TUESDAY NIGHT COULD BE A HAZARD. WIND CHILLS COULD ALSO POSE A
PROBLEM WITH VALUES DROPPING TO 10-15 DEGREES INLAND AND 15-20
DEGREES AT THE COAST.
SURFACE HIGH PRESSURE WILL BUILD IN FROM THE GULF OF MEXICO BY
WEDNESDAY...RESULTING IN RAIN FREE CONDITIONS AND A WARMING TREND
THROUGH FRIDAY. HIGH TEMPERATURES WILL REACH SEASONAL NORMALS IN
THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY. SOUTHERLY FLOW
WITHIN THE WARM SECTOR OF ANOTHER APPROACHING COLD FRONT WILL
ALLOW TEMPERATURES ON FRIDAY AND SATURDAY TO RISE ABOVE
NORMALS...IN THE MID TO UPPER 60S.
INTRODUCE A SLIGHT CHANCE OF RAIN ON SATURDAY AS THE COLD FRONT
DROPS INTO THE REGION FROM THE NORTHWEST. DUE TO SOME TIMING
ISSUES BETWEEN THE GFS AND ECMWF...HAVE MAINTAINED 20 PERCENT POPS
THROUGH THE WEEKEND.
&&
.AVIATION /16Z MONDAY THROUGH FRIDAY/...
VFR CONDITIONS WILL PREVAIL THROUGH THIS EVENING. RAIN...POSSIBLY
MIXED WITH SLEET OR SNOW...COULD IMPACT THE TERMINALS LATE TONIGHT
AS LOW PRESSURE DEVELOPS ACROSS THE SOUTH CAROLINA MIDLANDS. LOW
CONFIDENCE ON THE COVERAGE AND TIMING OF THE PRECIPITATION SO HAVE
OPTED TO LEAVE ALL MENTION OUT OF THE 12Z TAFS. TRENDS WILL BE
CAREFULLY MONITORED THROUGHOUT THE DAY AND PRECIPITATION MAY BE
INTRODUCED IN LATER TAF CYCLES.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW TUESDAY...ESPECIALLY AT KCHS.
OTHERWISE VFR WEATHER WILL PREVAIL THROUGH THE PERIOD.
&&
.MARINE...
QUICK UPDATE TO EXPIRE THE DENSE FOG ADVISORY FOG CHARLESTON
HARBOR. THERE IS STILL SOME PATCHY SEA FOG OVER THE NEARSHORE
COASTAL WATERS...BUT EXPECT THAT IT WILL BREAK UP OVER THE NEXT
COUPLE HOUR OR SO.
A TROUGH OF LOW PRESSURE WILL APPROACH FROM THE WEST TODAY...THEN
PUSH THROUGH THE WATERS LATE TONIGHT AS A STORM SYSTEM BEGINS TO
ORGANIZE OFF THE CAROLINA COAST. HAVE MADE SOME MINOR TWEAKS TO THE
COASTAL WATERS FORECAST...MAINLY TO REMOVE MORNING WORDING. HAVE
ALSO PUSHED THE SMALL CRAFT ADVISORY BACK ACROSS THE OUTER GEORGIA
WATERS AS WINDS AND SEAS ARE EXPECTED TO REMAIN BELOW HEADLINE
THRESHOLDS INTO THE EVENING.
SOUTHWEST WINDS WILL INCREASE TONIGHT AS A LOW-LEVEL JET MOVES
ACROSS THE WATERS. MIXING PROFILES WILL REMAIN LESS THAN IDEAL
ACROSS THE COOLER NEARSHORE WATERS SO WINDS WILL BE CAPPED AT 15-20
KT FOR NOW. WARMER CONDITIONS OVER THE GEORGIA OFFSHORE WATERS WILL
SUPPORT 20-25 KT.
TUESDAY THROUGH FRIDAY...COLD AIR ADVECTION AND A TIGHT PRESSURE
GRADIENT ON THE BACK SIDE OF A DEEPENING COASTAL LOW WILL MAINTAIN
STRONG WEST WINDS OVER THE MARINE ZONES TUESDAY. SMALL CRAFT
ADVISORY CONDITIONS WILL LIKELY BE REACHED FOR MOST OF THE COASTAL
WATERS...PERHAPS INCLUDING THE CHARLESTON HARBOR. WILL NEED TO
CLOSELY MONITOR MODEL TRENDS FOR POTENTIAL MARGINAL GALE FORCE
WINDS IN THE OUTER GEORGIA WATERS. AT THIS POINT...HAVE INDICATED
25 TO 30 KT WINDS FOR THE OFFSHORE GEORGIA ZONES WITH POSSIBLE
OCCASIONAL GALE FORCE GUSTS. FEEL THAT SEAS WILL BE 5 TO 7 FT IN
THE OUTER WATERS...MITIGATED SOMEWHAT BY THE OFFSHORE FLOW.
THE COASTAL LOW WILL QUICKLY DEPART TO THE NORTHEAST TUESDAY
AFTERNOON/EVENING...WITH HIGH PRESSURE BUILDING IN FROM THE GULF OF
MEXICO. EXPECT A GRADUAL DECREASE IN WEST WINDS WEDNESDAY...BECOMING
SOUTHWEST AS THE SURFACE HIGH SHIFTS OFF THE FLORIDA COAST LATE IN
THE WEEK.
A COLD FRONT WILL APPROACH FROM THE NORTHWEST OVER THE WEEKEND...BUT
THERE REMAINS A LOT OF UNCERTAINTY REGARDING TIMING AND STRENGTH
OF THE FEATURE.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 11 PM THIS EVENING TO 11 AM EST
WEDNESDAY FOR AMZ374.
&&
$$
33/JRJ
000
FXUS62 KCHS 191132
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
632 AM EST MON JAN 19 2009
...WINTER WEATHER POSSIBLE LATE TONIGHT AND TUESDAY...
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP ALONG A DESCENDING COLD FRONT EARLY
TUESDAY AND PULL NORTHEAST OFF THE CAROLINA COAST BY TUESDAY
AFTERNOON. HIGH PRESSURE WILL THEN BUILD INTO THE AREA THROUGH
FRIDAY...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
WIDESPREAD DENSE FOG PERSISTS ACROSS A GOOD PORTION OF SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA EARLY THIS MORNING WITH MOST
LOCALES REPORTING VISIBILITIES 1/4 MILE OR LESS. VISIBILITIES HAVE
IMPROVED ABOVE 1 MILE ALONG THE INTERSTATE 95 CORRIDOR FROM
SAVANNAH SOUTH TO DARIEN THERE A BATCH OF THICK MID-LEVEL CLOUDS
MOVED THROUGH EARLIER BUT EXPECT CONDITIONS TO DETERIORATE BACK
TO DENSE FOG ADVISORY LEVELS SHORTLY AS SKIES CLEAR. THE DENSE FOG
ADVISORY WILL BE EXTENDED UNTIL 9 AM TO COVER ONGOING TRENDS.
MESONET OBSERVATIONS AND HIGH RESOLUTION LAPS DATA SUGGEST
TEMPERATURES ARE AT OR JUST ABOVE FREEZING ROUGHLY NORTH OF A LINE
FROM MILLHAVEN EAST TO ALLENDALE-WILLIAMS AND SAINT GEORGE. CAN
NOT RULE A FEW PATCHES OF FREEZING FOG IN THIS AREA WHICH COULD
PRODUCE SOME ISOLATED INSTANCES OF ICING ON BRIDGES AND
OVERPASSES...BUT THE COVERAGE AND IMPACT IS NOT HIGH ENOUGH TO
JUSTIFY A FREEZING FOG ADVISORY IN THESE AREAS JUST YET. WILL
CONTINUE TO MONITOR AND UPDATE IF NEEDED.
A MULTITUDE OF UPSTREAM SHORTWAVES WILL HELP TO REINFORCE A VERY
DEEP AND COLD LONG-WAVE TROUGH ACROSS THE EASTERN U.S. TODAY.
DENSE FOG WILL QUICKLY BURN OFF BY MID MORNING WITH THE VARIOUS
FOG LAYERS POSSIBLY LIFTING IN A SHALLOW CUMULUS FIELD. THICKER
CLOUD COVER UPSTREAM WILL MOVE IN FROM THE WEST THIS AFTERNOON AS
A SHORTWAVE ENERGY MOVING THROUGH EASTERN TENNESSEE PIVOTS AROUND
THE BASE OF THE LONG-WAVE TROUGH. THE END RESULT WILL BE MOSTLY
CLEAR TO PARTLY CLOUDY SKIES GIVING WAY TO MOSTLY CLOUDY SKIES
THIS AFTERNOON WITH HIGHS FROM THE MID 50S WELL INLAND TO THE
LOWER 60S ACROSS THE FAR SOUTH ALONG THE ALTAMAHA RIVER.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/...
ANOTHER IN A SERIES OF SHORTWAVE TROUGHS WILL ROUND THE BASE OF
THE AMPLIFYING LONG-WAVE TROUGH TONIGHT. THE NAM/GFS AND ECMWF
HAS FINALLY COME INTO SOME SORT OF AGREEMENT THAT THE APPROACHING
SHORTWAVE WILL INITIATE CYCLOGENESIS ACROSS THE MIDLANDS THIS
EVENING WITH THE DEVELOPING LOW REFORMING OFF THE NORTHEAST SOUTH
CAROLINA COAST BY SUNRISE TUESDAY WHERE LOW-LEVEL BAROCLINICITY
IS THE GREATEST. STRONG UPWARD FORCING AHEAD OF THE SHORTWAVE INDUCED
BY IMPRESSIVE 500-300MB Q-VECTOR CONVERGENCE AND INCREASING
ISENTROPIC ASSENT WILL LIKELY SUPPORT AT LEAST PATCHY PRECIPITATION
AFTER MIDNIGHT WITH THE PRECIPITATION INCREASING IN BOTH COVERAGE
AND INTENSITY AS SUNRISE APPROACHES. WITH TEMPERATURES FALLING INTO
THE 30S AND TEMPERATURES ABOVE THE BOUNDARY LAYER PROGGED TO DROPPED
BELOW FREEZING...SOME P-TYPE PROBLEMS APPEAR LIKELY WELL INLAND FROM
THE COAST.
MODEL AND BUFKIT SOUNDINGS SUGGEST THAT ALTHOUGH THE LOWER
TROPOSPHERE WILL SUFFICIENTLY MOISTEN TO SUPPORT PRECIPITATION
THROUGH THE NIGHT...THE ATMOSPHERE LOOKS ONLY MARGINALLY FAVORABLE
TO SUPPORT ICE FORMATION WITHIN THE FAVORABLE -10 TO -20C
DENDRITIC GROWTH ZONE. THIS TYPE OF THERMAL SETUP WOULD TYPICALLY
YIELD A MIXTURE OF RAIN AND SLEET BUT GIVEN THE STRENGTH OF Q-C
FORCING WE BELIEVE ANY RAIN WILL MIX WITH OR CHANGE TO SNOW LATE IN
THE NIGHT WELL INLAND FROM THE COAST. IN FACT...CRITICAL LOW-LEVEL
THICKNESSES SUPPORT A CHANGE OVER TO ALL SNOW ACROSS THE ENTIRE
FORECAST AREA AFTER 10Z AS THE BAND OF STRONGEST UPPER FORCING AND
ASSOCIATED DYNAMIC COOLING MOVE IN FROM THE WEST. PLAN TO BE FAIRLY
CONSERVATIVE WITH POPS TONIGHT GOING NO HIGHER THAN 20-30 PERCENT.
WILL SHOW RAIN SHOWERS CHANGING TO SNOW IN A CORRIDOR FROM ALLENDALE
EAST TO NORTHERN COLLETON WITH THE RAIN BECOMING MIXED WITH SNOW
ACROSS DORCHESTER AND BERKELEY. THERE MAY EVEN BE A SMALL CORRIDOR
OF FREEZING RAIN FROM NORTHERN PORTIONS OF EFFINGHAM AND INLAND
JASPER IF TEMPERATURES CAN DROP TO FREEZING WITH RAIN EXPECTED
ELSEWHERE. EXPECT LITTLE OR NO ICE/SLEET/SNOW ACCUMULATIONS
THROUGH SUNRISE SO NO ADVISORIES...WATCHES OR WARNINGS ARE PLANNED
AT THIS TIME FOR THIS TIME PERIOD.
LOWS WILL RANGE FROM THE UPPER 20S TO AROUND 30 ACROSS FAR
INTERIOR SOUTHEAST GEORGIA TO THE MID 30S ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS ARE IN FAIRLY GOOD AGREEMENT INDICATING WRAP AROUND PRECIP
AFFECTING AREAS MAINLY NORTH OF INTERSTATE 16 EARLY TUESDAY
MORNING...AS LOW PRESSURE OFF THE CAROLINA COAST DEEPENS AND SHIFTS
NORTHEAST. COLD AIR WILL ADVECT INTO THE REGION ON THE BACK SIDE
OF THE COASTAL LOW...AND TEMPERATURES WILL REMAIN IN THE LOWER 30S
FOR THE FIRST FEW HOURS AFTER SUNRISE. CONSIDERING THE STRONG UPPER
LEVEL DYNAMICS DUE TO AN AMPLIFIED UPPER TROUGH AND PLENTY OF VORT
ENERGY...SNOW SHOWERS ARE POSSIBLE WITHIN THE COLD AIR MASS
TUESDAY MORNING. PRECIP CHANCES WILL DIMINISH TUESDAY
AFTERNOON...HOWEVER ANY LIGHT SHOWERS WILL LIKELY BE MIXED WITH
SNOW. SREF SNOW PROBABILITIES ARE UP TO 40 PERCENT TUESDAY...WITH
GFS AND NAM BOTH INDICATING 12 HOUR SNOW ACCUMULATIONS POTENTIALLY
UP TO 0.5 INCH IN THE FAR INLAND SECTIONS FROM BERKELEY COUNTY
SOUTHWEST TO ALLENDALE COUNTY.
HAVE INDICATED A SOLID CHANCE OF SNOW SHOWERS FOR ALL OF THE SOUTH
CAROLINA ZONES TUESDAY MORNING...WITH PRECIP CHANCES DIMINISHING
TO THE SOUTH. AFTER 15Z...MENTION RAIN SHOWERS MIXED WITH SNOW
SHOWERS...THEN RAIN/SNOW CHANCES DROPPING TO AROUND 20 PERCENT
AFTER 18Z. UPON COLLABORATION WITH HPC AND SURROUNDING OFFICES...
HAVE OPTED TO HOLD OFF ON ANY WATCHES OR ADVISORIES AT THIS POINT.
HOWEVER...A WINTER WEATHER ADVISORY OR WINTER STORM WATCH/WARNING
MAY BE ISSUED BY SUBSEQUENT SHIFTS AS THE EVENT APPROACHES.
TEMPERATURES WILL BE SUPPRESSED IN THE LOWER 40S ON TUESDAY...WITH
OVERNIGHT LOWS DROPPING INTO THE 20S. CONSIDERING THE
PRECIPITATION OCCURRING DURING THE DAY...ICE FORMATION ON ROADS
TUESDAY NIGHT COULD BE A HAZARD. WIND CHILLS COULD ALSO POSE A
PROBLEM WITH VALUES DROPPING TO 10-15 DEGREES INLAND AND 15-20
DEGREES AT THE COAST.
SURFACE HIGH PRESSURE WILL BUILD IN FROM THE GULF OF MEXICO BY
WEDNESDAY...RESULTING IN RAIN FREE CONDITIONS AND A WARMING TREND
THROUGH FRIDAY. HIGH TEMPERATURES WILL REACH SEASONAL NORMALS IN
THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY. SOUTHERLY FLOW
WITHIN THE WARM SECTOR OF ANOTHER APPROACHING COLD FRONT WILL
ALLOW TEMPERATURES ON FRIDAY AND SATURDAY TO RISE ABOVE
NORMALS...IN THE MID TO UPPER 60S.
INTRODUCE A SLIGHT CHANCE OF RAIN ON SATURDAY AS THE COLD FRONT
DROPS INTO THE REGION FROM THE NORTHWEST. DUE TO SOME TIMING
ISSUES BETWEEN THE GFS AND ECMWF...HAVE MAINTAINED 20 PERCENT POPS
THROUGH THE WEEKEND.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
LOOK FOR DENSE FOG TO BREAK BETWEEN 13-14Z WITH CONDITIONS
BECOMING VFR AT KCHS AND KSAV BY 15Z. VFR CONDITIONS WILL PREVAIL
THROUGH THIS EVENING WITH CEILINGS DROPPING DOWN TO AROUND 5000 FT
THIS AFTERNOON. RAIN...POSSIBLY MIXED WITH SLEET OR SNOW...COULD
IMPACT THE TERMINALS LATE TONIGHT AS LOW PRESSURE DEVELOPS ACROSS
THE SOUTH CAROLINA MIDLANDS. LOW CONFIDENCE ON THE COVERAGE AND
TIMING OF THE PRECIPITATION SO HAVE OPTED TO LEAVE ALL MENTION OUT
OF THE 12Z TAFS. TRENDS WILL BE CAREFULLY MONITORED THROUGHOUT THE
DAY AND PRECIPITATION MAY BE INTRODUCED IN LATER TAF CYCLES.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW TUESDAY...ESPECIALLY AT KCHS.
OTHERWISE VFR WEATHER WILL PREVAIL THROUGH THE PERIOD.
&&
.MARINE...
LOOKS LIKE DENSE FOG WILL CONTINUE IN THE CHARLESTON HARBOR
THROUGH AT LEAST SUNRISE. REPORTS FROM PILOT BOAT CONTROL INDICATE
THE FOG IS SHUT DOWN TO ALL PORT TRAFFIC UNTIL CONDITIONS IMPROVE.
THE MARINE DENSE FOG ADVISORY WILL BE EXTENDED UNTIL 9 AM.
OTHERWISE ELEVATED SEAS CONTINUE TO IMPACT THE GEORGIA OFFSHORE
LEG WHERE LATEST TRENDS SUGGEST SEAS REMAIN ABOVE 6 FT. THIS IS
DIFFICULT TO VERIFY WITH THE BENEFIT OF SPAG1. ALTHOUGH SEAS WILL
LIKELY DROP BELOW 6 FT FOR A PERIOD THIS AFTERNOON CONDITIONS WILL
RAMP BACK UP TONIGHT AS LOW PRESSURE DEVELOPS ACROSS THE SOUTH
CAROLINA MIDLANDS. SEE NO REASON TO DROP THE ADVISORY DURING THE
AFTERNOON JUST TO BE REISSUED FOR TONIGHT. WESTERLY WINDS WILL
BECOME SOUTHWEST THIS AFTERNOON AND INCREASE TONIGHT AS A LOW-
LEVEL JET MOVES ACROSS THE WATERS. MIXING PROFILES WILL REMAIN
LESS THAN IDEAL ACROSS THE COOLER NEARSHORE WATERS SO WINDS WILL
BE CAPPED AT 15-20 KT FOR NOW. WARMER CONDITIONS OVER THE GEORGIA
OFFSHORE WATERS WILL SUPPORT 20-25 KT.
TUESDAY THROUGH FRIDAY...COLD AIR ADVECTION AND A TIGHT PRESSURE
GRADIENT ON THE BACK SIDE OF A DEEPENING COASTAL LOW WILL MAINTAIN
STRONG WEST WINDS OVER THE MARINE ZONES TUESDAY. SMALL CRAFT
ADVISORY CONDITIONS WILL LIKELY BE REACHED FOR MOST OF THE COASTAL
WATERS...PERHAPS INCLUDING THE CHARLESTON HARBOR. WILL NEED TO
CLOSELY MONITOR MODEL TRENDS FOR POTENTIAL MARGINAL GALE FORCE
WINDS IN THE OUTER GEORGIA WATERS. AT THIS POINT...HAVE INDICATED
25 TO 30 KT WINDS FOR THE OFFSHORE GEORGIA ZONES WITH POSSIBLE
OCCASIONAL GALE FORCE GUSTS. FEEL THAT SEAS WILL BE 5 TO 7 FT IN
THE OUTER WATERS...MITIGATED SOMEWHAT BY THE OFFSHORE FLOW.
THE COASTAL LOW WILL QUICKLY DEPART TO THE NORTHEAST TUESDAY
AFTERNOON/EVENING...WITH HIGH PRESSURE BUILDING IN FROM THE GULF OF
MEXICO. EXPECT A GRADUAL DECREASE IN WEST WINDS WEDNESDAY...BECOMING
SOUTHWEST AS THE SURFACE HIGH SHIFTS OFF THE FLORIDA COAST LATE IN
THE WEEK.
A COLD FRONT WILL APPROACH FROM THE NORTHWEST OVER THE WEEKEND...BUT
THERE REMAINS A LOT OF UNCERTAINTY REGARDING TIMING AND STRENGTH
OF THE FEATURE.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR GAZ087-088-
099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR SCZ040-
042>045-047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR AMZ330.
&&
$$
ST
000
FXUS62 KCHS 190949 CCA
AFDCHS
AREA FORECAST DISCUSSION...CORRECTED
NATIONAL WEATHER SERVICE CHARLESTON SC
418 AM EST MON JAN 19 2009
...WINTER WEATHER POSSIBLE LATE TONIGHT AND TUESDAY...
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP ALONG A DESCENDING COLD FRONT EARLY
TUESDAY AND PULL NORTHEAST OFF THE CAROLINA COAST BY TUESDAY
AFTERNOON. HIGH PRESSURE WILL THEN BUILD INTO THE AREA THROUGH
FRIDAY...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /THROUGH TODAY/...
WIDESPREAD DENSE FOG PERSISTS ACROSS A GOOD PORTION OF SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA EARLY THIS MORNING WITH MOST
LOCALES REPORTING VISIBILITIES 1/4 MILE OR LESS. VISIBILITIES HAVE
IMPROVED ABOVE 1 MILE ALONG THE INTERSTATE 95 CORRIDOR FROM
SAVANNAH SOUTH TO DARIEN THERE A BATCH OF THICK MID-LEVEL CLOUDS
MOVED THROUGH EARLIER BUT EXPECT CONDITIONS TO DETERIORATE BACK
TO DENSE FOG ADVISORY LEVELS SHORTLY AS SKIES CLEAR. THE DENSE FOG
ADVISORY WILL BE EXTENDED UNTIL 9 AM TO COVER ONGOING TRENDS.
MESONET OBSERVATIONS AND HIGH RESOLUTION LAPS DATA SUGGEST
TEMPERATURES ARE AT OR JUST ABOVE FREEZING ROUGHLY NORTH OF A LINE
FROM MILLHAVEN EAST TO ALLENDALE-WILLIAMS AND SAINT GEORGE. CAN
NOT RULE A FEW PATCHES OF FREEZING FOG IN THIS AREA WHICH COULD
PRODUCE SOME ISOLATED INSTANCES OF ICING ON BRIDGES AND
OVERPASSES...BUT THE COVERAGE AND IMPACT IS NOT HIGH ENOUGH TO
JUSTIFY A FREEZING FOG ADVISORY IN THESE AREAS JUST YET. WILL
CONTINUE TO MONITOR AND UPDATE IF NEEDED.
A MULTITUDE OF UPSTREAM SHORTWAVES WILL HELP TO REINFORCE A VERY
DEEP AND COLD LONG-WAVE TROUGH ACROSS THE EASTERN U.S. TODAY.
DENSE FOG WILL QUICKLY BURN OFF BY MID MORNING WITH THE VARIOUS
FOG LAYERS POSSIBLY LIFTING IN A SHALLOW CUMULUS FIELD. THICKER
CLOUD COVER UPSTREAM WILL MOVE IN FROM THE WEST THIS AFTERNOON AS
A SHORTWAVE ENERGY MOVING THROUGH EASTERN TENNESSEE PIVOTS AROUND
THE BASE OF THE LONG-WAVE TROUGH. THE END RESULT WILL BE MOSTLY
CLEAR TO PARTLY CLOUDY SKIES GIVING WAY TO MOSTLY CLOUDY SKIES
THIS AFTERNOON WITH HIGHS FROM THE MID 50S WELL INLAND TO THE
LOWER 60S ACROSS THE FAR SOUTH ALONG THE ALTAMAHA RIVER.
&&
.SHORT TERM /TONIGHT/...
ANOTHER IN A SERIES OF SHORTWAVE TROUGHS WILL ROUND THE BASE OF
THE AMPLIFYING LONG-WAVE TROUGH TONIGHT. THE NAM/GFS AND ECMWF
HAS FINALLY COME INTO SOME SORT OF AGREEMENT THAT THE APPROACHING
SHORTWAVE WILL INITIATE CYCLOGENESIS ACROSS THE MIDLANDS THIS
EVENING WITH THE DEVELOPING LOW REFORMING OFF THE NORTHEAST SOUTH
CAROLINA COAST BY SUNRISE TUESDAY WHERE LOW-LEVEL BAROCLINICITY
IS THE GREATEST. STRONG UPWARD FORCING AHEAD OF THE SHORTWAVE INDUCED
BY IMPRESSIVE 500-300MB Q-VECTOR CONVERGENCE AND INCREASING
ISENTROPIC ASSENT WILL LIKELY SUPPORT AT LEAST PATCHY PRECIPITATION
AFTER MIDNIGHT WITH THE PRECIPITATION INCREASING IN BOTH COVERAGE
AND INTENSITY AS SUNRISE APPROACHES. WITH TEMPERATURES FALLING INTO
THE 30S AND TEMPERATURES ABOVE THE BOUNDARY LAYER PROGGED TO DROPPED
BELOW FREEZING...SOME P-TYPE PROBLEMS APPEAR LIKELY WELL INLAND FROM
THE COAST.
MODEL AND BUFKIT SOUNDINGS SUGGEST THAT ALTHOUGH THE LOWER
TROPOSPHERE WILL SUFFICIENTLY MOISTEN TO SUPPORT PRECIPITATION
THROUGH THE NIGHT...THE ATMOSPHERE LOOKS ONLY MARGINALLY FAVORABLE
TO SUPPORT ICE FORMATION WITHIN THE FAVORABLE -10 TO -20C
DENDRITIC GROWTH ZONE. THIS TYPE OF THERMAL SETUP WOULD TYPICALLY
YIELD A MIXTURE OF RAIN AND SLEET BUT GIVEN THE STRENGTH OF Q-C
FORCING WE BELIEVE ANY RAIN WILL MIX WITH OR CHANGE TO SNOW LATE IN
THE NIGHT WELL INLAND FROM THE COAST. IN FACT...CRITICAL LOW-LEVEL
THICKNESSES SUPPORT A CHANGE OVER TO ALL SNOW ACROSS THE ENTIRE
FORECAST AREA AFTER 10Z AS THE BAND OF STRONGEST UPPER FORCING AND
ASSOCIATED DYNAMIC COOLING MOVE IN FROM THE WEST. PLAN TO BE FAIRLY
CONSERVATIVE WITH POPS TONIGHT GOING NO HIGHER THAN 20-30 PERCENT.
WILL SHOW RAIN SHOWERS CHANGING TO SNOW IN A CORRIDOR FROM ALLENDALE
EAST TO NORTHERN COLLETON WITH THE RAIN BECOMING MIXED WITH SNOW
ACROSS DORCHESTER AND BERKELEY. THERE MAY EVEN BE A SMALL CORRIDOR
OF FREEZING RAIN FROM NORTHERN PORTIONS OF EFFINGHAM AND INLAND
JASPER IF TEMPERATURES DROP TO FREEZING THERE WITH RAIN EXPECTED
ELSEWHERE. EXPECT LITTLE OR NO ICE/SLEET/SNOW ACCUMULATIONS THROUGH
SUNRISE SO NO ADVISORIES...WATCHES OR WARNINGS ARE PLANNED AT THIS
TIME FOR THIS TIME PERIOD.
LOWS WILL RANGE FROM THE UPPER 20S TO AROUND 30 ACROSS FAR
INTERIOR SOUTHEAST GEORGIA TO THE MID 30S ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS ARE IN FAIRLY GOOD AGREEMENT INDICATING WRAP AROUND PRECIP
AFFECTING AREAS MAINLY NORTH OF INTERSTATE 16 EARLY TUESDAY
MORNING...AS LOW PRESSURE OFF THE CAROLINA COAST DEEPENS AND SHIFTS
NORTHEAST. COLD AIR WILL ADVECT INTO THE REGION ON THE BACK SIDE
OF THE COASTAL LOW...AND TEMPERATURES WILL REMAIN IN THE LOWER 30S
FOR THE FIRST FEW HOURS AFTER SUNRISE. CONSIDERING THE STRONG UPPER
LEVEL DYNAMICS DUE TO AN AMPLIFIED UPPER TROUGH AND PLENTY OF VORT
ENERGY...SNOW SHOWERS ARE POSSIBLE WITHIN THE COLD AIR MASS
TUESDAY MORNING. PRECIP CHANCES WILL DIMINISH TUESDAY
AFTERNOON...HOWEVER ANY LIGHT SHOWERS WILL LIKELY BE MIXED WITH
SNOW. SREF SNOW PROBABILITIES ARE UP TO 40 PERCENT TUESDAY...WITH
GFS AND NAM BOTH INDICATING 12 HOUR SNOW ACCUMULATIONS POTENTIALLY
UP TO 0.5 INCH IN THE FAR INLAND SECTIONS FROM BERKELEY COUNTY
SOUTHWEST TO ALLENDALE COUNTY.
HAVE INDICATED A SOLID CHANCE OF SNOW SHOWERS FOR ALL OF THE SOUTH
CAROLINA ZONES TUESDAY MORNING...WITH PRECIP CHANCES DIMINISHING
TO THE SOUTH. AFTER 15Z...MENTION RAIN SHOWERS MIXED WITH SNOW
SHOWERS...THEN RAIN/SNOW CHANCES DROPPING TO AROUND 20 PERCENT
AFTER 18Z. UPON COLLABORATION WITH HPC AND SURROUNDING OFFICES...
HAVE OPTED TO HOLD OFF ON ANY WATCHES OR ADVISORIES AT THIS POINT.
HOWEVER...A WINTER WEATHER ADVISORY OR WINTER STORM WATCH/WARNING
MAY BE ISSUED BY SUBSEQUENT SHIFTS AS THE EVENT APPROACHES.
TEMPERATURES WILL BE SUPPRESSED IN THE LOWER 40S ON TUESDAY...WITH
OVERNIGHT LOWS DROPPING INTO THE 20S. CONSIDERING THE
PRECIPITATION OCCURRING DURING THE DAY...ICE FORMATION ON ROADS
TUESDAY NIGHT COULD BE A HAZARD. WIND CHILLS COULD ALSO POSE A
PROBLEM WITH VALUES DROPPING TO 10-15 DEGREES INLAND AND 15-20
DEGREES AT THE COAST.
SURFACE HIGH PRESSURE WILL BUILD IN FROM THE GULF OF MEXICO BY
WEDNESDAY...RESULTING IN RAIN FREE CONDITIONS AND A WARMING TREND
THROUGH FRIDAY. HIGH TEMPERATURES WILL REACH SEASONAL NORMALS IN
THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY. SOUTHERLY FLOW
WITHIN THE WARM SECTOR OF ANOTHER APPROACHING COLD FRONT WILL
ALLOW TEMPERATURES ON FRIDAY AND SATURDAY TO RISE ABOVE
NORMALS...IN THE MID TO UPPER 60S.
INTRODUCE A SLIGHT CHANCE OF RAIN ON SATURDAY AS THE COLD FRONT
DROPS INTO THE REGION FROM THE NORTHWEST. DUE TO SOME TIMING
ISSUES BETWEEN THE GFS AND ECMWF...HAVE MAINTAINED 20 PERCENT POPS
THROUGH THE WEEKEND.
&&
.AVIATION /08Z MONDAY THROUGH FRIDAY/...
DENSE FOG WILL PLAGUE THE TERMINALS FOR SEVERAL MORE HOURS UNTIL
DRIER AIR WORKS IN FROM THE WEST. VISIBILITIES HAVE TEMPORARILY
IMPROVED AT KSAV WHERE A BAND OF MID-LVL CLOUDINESS IS SKIRTING
THROUGH. EXPECT VISIBILITIES TO CRASH BY 08Z AGAIN AS THE CLOUDS
MOVE OFF TO THE NORTHEAST. THERE IS A POSSIBILITY THAT
VISIBILITIES MAY IMPROVE QUICKER THAN 12Z...ESPECIALLY IF THE
DRIER AIR TO THE WEST WORKS IN QUICKER THAN EXPECTED. AMENDMENTS
WILL MOST CERTAINLY BE ISSUED THROUGHOUT THE EARLY MORNING. EXPECT
VFR CONDITIONS TO PREVAIL BY 14Z WITH GUSTY WINDS POSSIBLE BY LATE
MORNING.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
LOOKS LIKE DENSE FOG WILL CONTINUE IN THE CHARLESTON HARBOR
THROUGH AT LEAST SUNRISE. REPORTS FROM PILOT BOAT CONTROL INDICATE
THE FOG IS SHUT DOWN TO ALL PORT TRAFFIC UNTIL CONDITIONS IMPROVE.
THE MARINE DENSE FOG ADVISORY WILL BE EXTENDED UNTIL 9 AM.
OTHERWISE ELEVATED SEAS CONTINUE TO IMPACT THE GEORGIA OFFSHORE
LEG WHERE LATEST TRENDS SUGGEST SEAS REMAIN ABOVE 6 FT. THIS IS
DIFFICULT TO VERIFY WITH THE BENEFIT OF SPAG1. ALTHOUGH SEAS WILL
LIKELY DROP BELOW 6 FT FOR A PERIOD THIS AFTERNOON CONDITIONS WILL
RAMP BACK UP TONIGHT AS LOW PRESSURE DEVELOPS ACROSS THE SOUTH
CAROLINA MIDLANDS. SEE NO REASON TO DROP THE ADVISORY DURING THE
AFTERNOON JUST TO BE REISSUED FOR TONIGHT. WESTERLY WINDS WILL
BECOME SOUTHWEST THIS AFTERNOON AND INCREASE TONIGHT AS A LOW-
LEVEL JET MOVES ACROSS THE WATERS. MIXING PROFILES WILL REMAIN
LESS THAN IDEAL ACROSS THE COOLER NEARSHORE WATERS SO WINDS WILL
BE CAPPED AT 15-20 KT FOR NOW. WARMER CONDITIONS OVER THE GEORGIA
OFFSHORE WATERS WILL SUPPORT 20-25 KT.
TUESDAY THROUGH FRIDAY...COLD AIR ADVECTION AND A TIGHT PRESSURE
GRADIENT ON THE BACK SIDE OF A DEEPENING COASTAL LOW WILL MAINTAIN
STRONG WEST WINDS OVER THE MARINE ZONES TUESDAY. SMALL CRAFT
ADVISORY CONDITIONS WILL LIKELY BE REACHED FOR MOST OF THE COASTAL
WATERS...PERHAPS INCLUDING THE CHARLESTON HARBOR. WILL NEED TO
CLOSELY MONITOR MODEL TRENDS FOR POTENTIAL MARGINAL GALE FORCE
WINDS IN THE OUTER GEORGIA WATERS. AT THIS POINT...HAVE INDICATED
25 TO 30 KT WINDS FOR THE OFFSHORE GEORGIA ZONES WITH POSSIBLE
OCCASIONAL GALE FORCE GUSTS. FEEL THAT SEAS WILL BE 5 TO 7 FT IN
THE OUTER WATERS...MITIGATED SOMEWHAT BY THE OFFSHORE FLOW.
THE COASTAL LOW WILL QUICKLY DEPART TO THE NORTHEAST TUESDAY
AFTERNOON/EVENING...WITH HIGH PRESSURE BUILDING IN FROM THE GULF OF
MEXICO. EXPECT A GRADUAL DECREASE IN WEST WINDS WEDNESDAY...BECOMING
SOUTHWEST AS THE SURFACE HIGH SHIFTS OFF THE FLORIDA COAST LATE IN
THE WEEK.
A COLD FRONT WILL APPROACH FROM THE NORTHWEST OVER THE WEEKEND...BUT
THERE REMAINS A LOT OF UNCERTAINTY REGARDING TIMING AND STRENGTH
OF THE FEATURE.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR GAZ087-088-
099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR SCZ040-
042>045-047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR AMZ330.
&&
$$
ST/79
000
FXUS62 KCHS 190918
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
418 AM EST MON JAN 19 2009
...WINTER WEATHER POSSIBLE LATE TONIGHT AND TUESDAY...
.SYNOPSIS...
LOW PRESSURE WILL DEVELOP ALONG A DESCENDING COLD FRONT EARLY
TUESDAY AND PULL NORTHEAST OFF THE CAROLINA COAST BY TUESDAY
AFTERNOON. HIGH PRESSURE WILL THEN BUILD INTO THE AREA THROUGH
FRIDAY...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /THROUGH TODAY/...
WIDESPREAD DENSE FOG PERSISTS ACROSS A GOOD PORTION OF SOUTHEAST
SOUTH CAROLINA AND SOUTHEAST GEORGIA EARLY THIS MORNING WITH MOST
LOCALES REPORTING VISIBILITIES 1/4 MILE OR LESS. VISIBILITIES HAVE
IMPROVED ABOVE 1 MILE ALONG THE INTERSTATE 95 CORRIDOR FROM
SAVANNAH SOUTH TO DARIEN THERE A BATCH OF THICK MID-LEVEL CLOUDS
MOVED THROUGH EARLIER BUT EXPECT CONDITIONS TO DETERIORATE BACK
TO DENSE FOG ADVISORY LEVELS SHORTLY AS SKIES CLEAR. THE DENSE FOG
ADVISORY WILL BE EXTENDED UNTIL 9 AM TO COVER ONGOING TRENDS.
MESONET OBSERVATIONS AND HIGH RESOLUTION LAPS DATA SUGGEST
TEMPERATURES ARE AT OR JUST ABOVE FREEZING ROUGHLY NORTH OF A LINE
FROM MILLHAVEN EAST TO ALLENDALE-WILLIAMS AND SAINT GEORGE. CAN
NOT RULE A FEW PATCHES OF FREEZING FOG IN THIS AREA WHICH COULD
PRODUCE SOME ISOLATED INSTANCES OF ICING ON BRIDGES AND
OVERPASSES...BUT THE COVERAGE AND IMPACT IS NOT HIGH ENOUGH TO
JUSTIFY A FREEZING FOG ADVISORY IN THESE AREAS JUST YET. WILL
CONTINUE TO MONITOR AND UPDATE IF NEEDED.
A MULTITUDE OF UPSTREAM SHORTWAVES WILL HELP TO REINFORCE A VERY
DEEP AND COLD LONG-WAVE TROUGH ACROSS THE EASTERN U.S. TODAY.
DENSE FOG WILL QUICKLY BURN OFF BY MID MORNING WITH THE VARIOUS
FOG LAYERS POSSIBLY LIFTING IN A SHALLOW CUMULUS FIELD. THICKER
CLOUD COVER UPSTREAM WILL MOVE IN FROM THE WEST THIS AFTERNOON AS
A SHORTWAVE ENERGY MOVING THROUGH EASTERN TENNESSEE PIVOTS AROUND
THE BASE OF THE LONG-WAVE TROUGH. THE END RESULT WILL BE MOSTLY
CLEAR TO PARTLY CLOUDY SKIES GIVING WAY TO MOSTLY CLOUDY SKIES
THIS AFTERNOON WITH HIGHS FROM THE MID 50S WELL INLAND TO THE
LOWER 60S ACROSS THE FAR SOUTH ALONG THE ALTAMAHA RIVER.
&&
.SHORT TERM /TONIGHT/...
ANOTHER IN A SERIES OF SHORTWAVE TROUGHS WILL ROUND THE BASE OF
THE AMPLIFYING LONG-WAVE TROUGH TONIGHT. THE NAM/GFS AND ECMWF
HAS FINALLY COME INTO SOME SORT OF AGREEMENT THAT THE APPROACHING
SHORTWAVE WILL INITIATE CYCLOGENESIS ACROSS THE MIDLANDS THIS
EVENING WITH THE DEVELOPING LOW REFORMING OFF THE NORTHEAST SOUTH
CAROLINA COAST BY SUNRISE TUESDAY WHERE LOW-LEVEL BAROCLINICITY
IS THE GREATEST. STRONG UPWARD FORCING AHEAD OF THE SHORTWAVE INDUCED
IMPRESSIVE 500-300MB Q-VECTOR CONVERGENCE AND INCREASING ISENTROPIC
ASSENT WILL LIKELY SUPPORT AT LEAST PATCHY PRECIPITATION AFTER
MIDNIGHT WITH THE PRECIPITATION INCREASING IN BOTH COVERAGE AND
INTENSITY AS SUNRISE APPROACHES. WITH TEMPERATURES FALLING INTO
THE 30S AND TEMPERATURES ABOVE THE BOUNDARY LAYER PROGGED TO
DROPPED BELOW FREEZING...SOME P-TYPE PROBLEMS APPEAR LIKELY WELL
INLAND FROM THE COAST.
MODEL AND BUFKIT SOUNDINGS SUGGEST THAT ALTHOUGH THE LOWER
TROPOSPHERE WILL SUFFICIENTLY MOISTEN TO SUPPORT PRECIPITATION
THROUGH THE NIGHT...THE ATMOSPHERE LOOKS ONLY MARGINALLY FAVORABLE
TO SUPPORT ICE FORMATION WITHIN THE FAVORABLE -10 TO -20C
DENDRITIC GROWTH ZONE. THIS TYPE OF THERMAL SETUP WOULD TYPICALLY
YIELD A MIXTURE OF RAIN AND SLEET BUT GIVEN THE STRENGTH OF Q-C
FORCING WE BELIEVE ANY RAIN WILL LIKELY MIX WITH OR CHANGE TO SNOW
LATE IN THE NIGHT WELL INLAND FROM THE COAST. IN FACT...CRITICAL
LOW-LEVEL THICKNESSES SUPPORT A CHANGE OVER TO ALL SNOW AFTER 10Z
ACROSS THE ENTIRE FORECAST AREA AS THE BAND STRONGEST UPPER
FORCING AND ASSOCIATED DYNAMIC COOLING MOVES IN. PLAN TO BE FAIRLY
CONSERVATIVE WITH POPS TONIGHT GOING NO HIGHER THAN 20-30 PERCENT.
WILL SHOW RAIN SHOWERS CHANGING TO SNOW IN A CORRIDOR FROM
ALLENDALE EAST TO NORTHERN COLLETON WITH THE RAIN BECOMING MIXED
WITH SNOW ACROSS DORCHESTER AND BERKELEY. THERE MAY EVEN BE A
SMALL CORRIDOR OF FREEZING RAIN FROM ACROSS NORTHERN PORTIONS OF
EFFINGHAM AND INLAND JASPER IF TEMPERATURES DROP TO FREEZING THERE
WITH EXPECTED ELSEWHERE. EXPECT LITTLE OR NO ICE/SLEET/SNOW
ACCUMULATIONS THROUGH SUNRISE SO NO ADVISORIES...WATCHES OR
WARNINGS ARE PLANNED FOR THIS PERIOD AT THIS TIME.
LOWS WILL RANGE FROM THE UPPER 20S TO AROUND 30 ACROSS FAR
INTERIOR SOUTHEAST GEORGIA TO THE MID 30S ALONG AND EAST OF THE
INTERSTATE 95 CORRIDOR.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
MODELS ARE IN FAIRLY GOOD AGREEMENT INDICATING WRAP AROUND PRECIP
AFFECTING AREAS MAINLY NORTH OF INTERSTATE 16 EARLY TUESDAY
MORNING...AS LOW PRESSURE OFF THE CAROLINA COAST DEEPENS AND SHIFTS
NORTHEAST. COLD AIR WILL ADVECT INTO THE REGION ON THE BACK SIDE
OF THE COASTAL LOW...AND TEMPERATURES WILL REMAIN IN THE LOWER 30S
FOR THE FIRST FEW HOURS AFTER SUNRISE. CONSIDERING THE STRONG UPPER
LEVEL DYNAMICS DUE TO AN AMPLIFIED UPPER TROUGH AND PLENTY OF VORT
ENERGY...SNOW SHOWERS ARE POSSIBLE WITHIN THE COLD AIR MASS
TUESDAY MORNING. PRECIP CHANCES WILL DIMINISH TUESDAY
AFTERNOON...HOWEVER ANY LIGHT SHOWERS WILL LIKELY BE MIXED WITH
SNOW. SREF SNOW PROBABILITIES ARE UP TO 40 PERCENT TUESDAY...WITH
GFS AND NAM BOTH INDICATING 12 HOUR SNOW ACCUMULATIONS POTENTIALLY
UP TO 0.5 INCH IN THE FAR INLAND SECTIONS FROM BERKELEY COUNTY
SOUTHWEST TO ALLENDALE COUNTY.
HAVE INDICATED A SOLID CHANCE OF SNOW SHOWERS FOR ALL OF THE SOUTH
CAROLINA ZONES TUESDAY MORNING...WITH PRECIP CHANCES DIMINISHING
TO THE SOUTH. AFTER 15Z...MENTION RAIN SHOWERS MIXED WITH SNOW
SHOWERS...THEN RAIN/SNOW CHANCES DROPPING TO AROUND 20 PERCENT
AFTER 18Z. UPON COLLABORATION WITH HPC AND SURROUNDING OFFICES...
HAVE OPTED TO HOLD OFF ON ANY WATCHES OR ADVISORIES AT THIS POINT.
HOWEVER...A WINTER WEATHER ADVISORY OR WINTER STORM WATCH/WARNING
MAY BE ISSUED BY SUBSEQUENT SHIFTS AS THE EVENT APPROACHES.
TEMPERATURES WILL BE SUPPRESSED IN THE LOWER 40S ON TUESDAY...WITH
OVERNIGHT LOWS DROPPING INTO THE 20S. CONSIDERING THE
PRECIPITATION OCCURRING DURING THE DAY...ICE FORMATION ON ROADS
TUESDAY NIGHT COULD BE A HAZARD.
SURFACE HIGH PRESSURE WILL BUILD IN FROM THE GULF OF MEXICO BY
WEDNESDAY...RESULTING IN RAIN FREE CONDITIONS AND A WARMING TREND
THROUGH FRIDAY. HIGH TEMPERATURES WILL REACH SEASONAL NORMALS IN
THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY. SOUTHERLY FLOW
WITHIN THE WARM SECTOR OF ANOTHER APPROACHING COLD FRONT WILL
ALLOW TEMPERATURES ON FRIDAY AND SATURDAY TO RISE ABOVE
NORMALS...IN THE MID TO UPPER 60S.
INTRODUCE A SLIGHT CHANCE OF RAIN ON SATURDAY AS THE COLD FRONT
DROPS INTO THE REGION FROM THE NORTHWEST. DUE TO SOME TIMING
ISSUES BETWEEN THE GFS AND ECMWF...HAVE MAINTAINED 20 PERCENT POPS
THROUGH THE WEEKEND.
&&
.AVIATION /08Z MONDAY THROUGH FRIDAY/...
DENSE FOG WILL PLAGUE THE TERMINALS FOR SEVERAL MORE HOURS UNTIL
DRIER AIR WORKS IN FROM THE WEST. VISIBILITIES HAVE TEMPORARILY
IMPROVED AT KSAV WHERE A BAND OF MID-LVL CLOUDINESS IS SKIRTING
THROUGH. EXPECT VISIBILITIES TO CRASH BY 08Z AGAIN AS THE CLOUDS
MOVE OFF TO THE NORTHEAST. THERE IS A POSSIBILITY THAT
VISIBILITIES MAY IMPROVE QUICKER THAN 12Z...ESPECIALLY IF THE
DRIER AIR TO THE WEST WORKS IN QUICKER THAN EXPECTED. AMENDMENTS
WILL MOST CERTAINLY BE ISSUED THROUGHOUT THE EARLY MORNING. EXPECT
VFR CONDITIONS TO PREVAIL BY 14Z WITH GUSTY WINDS POSSIBLE BY LATE
MORNING.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
LOOKS LIKE DENSE FOG WILL CONTINUE IN THE CHARLESTON HARBOR
THROUGH AT LEAST SUNRISE. REPORTS FROM PILOT BOAT CONTROL INDICATE
THE FOG IS SHUT DOWN TO ALL PORT TRAFFIC UNTIL CONDITIONS IMPROVE.
THE MARINE DENSE FOG ADVISORY WILL BE EXTENDED UNTIL 9 AM.
OTHERWISE ELEVATED SEAS CONTINUE TO IMPACT THE GEORGIA OFFSHORE
LEG WHERE LATEST TRENDS SUGGEST SEAS REMAIN ABOVE 6 FT. THIS IS
DIFFICULT TO VERIFY WITH THE BENEFIT OF SPAG1. ALTHOUGH SEAS WILL
LIKELY DROP BELOW 6 FT FOR A PERIOD THIS AFTERNOON CONDITIONS WILL
RAMP BACK UP TONIGHT AS LOW PRESSURE DEVELOPS ACROSS THE SOUTH
CAROLINA MIDLANDS. SEE NO REASON TO DROP THE ADVISORY DURING THE
AFTERNOON JUST TO BE REISSUED FOR TONIGHT. WESTERLY WINDS WILL
BECOME SOUTHWEST THIS AFTERNOON AND INCREASE TONIGHT AS A LOW-
LEVEL JET MOVES ACROSS THE WATERS. MIXING PROFILES WILL REMAIN
LESS THAN IDEAL ACROSS THE COOLER NEARSHORE WATERS SO WINDS WILL
BE CAPPED AT 15-20 KT FOR NOW. WARMER CONDITIONS OVER THE GEORGIA
OFFSHORE WATERS WILL SUPPORT 20-25 KT.
TUESDAY THROUGH FRIDAY...COLD AIR ADVECTION AND A TIGHT PRESSURE
GRADIENT ON THE BACK SIDE OF A DEEPENING COASTAL LOW WILL MAINTAIN
STRONG WEST WINDS OVER THE MARINE ZONES TUESDAY. SMALL CRAFT
ADVISORY CONDITIONS WILL LIKELY BE REACHED FOR MOST OF THE COASTAL
WATERS...PERHAPS INCLUDING THE CHARLESTON HARBOR. WILL NEED TO
CLOSELY MONITOR MODEL TRENDS FOR POTENTIAL MARGINAL GALE FORCE
WINDS IN THE OUTER GEORGIA WATERS. AT THIS POINT...HAVE INDICATED
25 TO 30 KT WINDS FOR THE OFFSHORE GEORGIA ZONES WITH POSSIBLE
OCCASIONAL GALE FORCE GUSTS. FEEL THAT SEAS WILL BE 5 TO 7 FT IN
THE OUTER WATERS...MITIGATED SOMEWHAT BY THE OFFSHORE FLOW.
THE COASTAL LOW WILL QUICKLY DEPART TO THE NORTHEAST TUESDAY
AFTERNOON/EVENING...WITH HIGH PRESSURE BUILDING IN FROM THE GULF OF
MEXICO. EXPECT A GRADUAL DECREASE IN WEST WINDS WEDNESDAY...BECOMING
SOUTHWEST AS THE SURFACE HIGH SHIFTS OFF THE FLORIDA COAST LATE IN
THE WEEK.
A COLD FRONT WILL APPROACH FROM THE NORTHWEST OVER THE WEEKEND...BUT
THERE REMAINS A LOT OF UNCERTAINTY REGARDING TIMING AND STRENGTH
OF THE FEATURE.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR GAZ087-088-
099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR SCZ040-
042>045-047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
DENSE FOG ADVISORY UNTIL 9 AM EST THIS MORNING FOR AMZ330.
&&
$$
ST/79
000
FXUS62 KCHS 190544
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1244 AM EST MON JAN 19 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE OFFSHORE OVERNIGHT. A SECONDARY COLD FRONT
TO PUSH THROUGH LATE MONDAY INTO TUESDAY. LOW PRESSURE ALONG A
COLD FRONT OFF THE CAROLINAS TUESDAY MORNING WILL PULL AWAY TO THE
NE. A TRAILING COLD FRONT WILL PUSH EAST OF THE AREA LATE IN THE
DAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH LATE IN THE
WEEK...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
LATE SUNDAY EVENING...LINGERING RAIN/SHOWERS LINGERED OVER EXTREME
SOUTHERN COUNTIES...AND HAD OTHERWISE PUSHED INTO COASTAL WATERS.
IN THE WAKE OF THE WIDESPREAD RAIN EVENT...CLEARING SKIES AND A
WEAK SURFACE PRESSURE GRADIENT/LIGHT WINDS HAD CREATED CONDITIONS
IDEAL FOR DENSE FOG ACROSS THE REGION. EXPECT COVERAGE OF DENSE
FOG TO EXPAND FOR A TIME OVERNIGHT...AND DENSE FOG SHOULD IMPACT
AT LEAST PORTIONS OF THE ENTIRE REGION. THUS...ISSUED A DENSE FOG
ADVISORY FOR ALL AREAS.
ENDED THE ADVISORY AT 5 AM...AS UPSTREAM DRIER AIR MAY SPREAD INTO
THE REGION AND MAY MITIGATE THE THREAT FOR DENSE FOG BEFORE
MIDNIGHT. HOWEVER...THE MID SHIFT MAY OPT TO EXTEND THE ADVISORY
PAST DAYBREAK IF THE EXPECTED DRYING FAILS TO DEVELOP.
FURTHER...THERE IS A SLIGHT CHANCE THAT TEMPERATURES COULD FALL TO
AROUND FREEZING ACROSS FAR INLAND AREAS LATE...SUPPORTING ICY
PATCHES ON SOME ROADS EARLY MONDAY MORNING. THIS FORECAST
CONTINUES TO HOLD LOW TEMPERATURES JUST ABOVE FREEZING.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 AM TUESDAY/...
MONDAY...SW FLOW WILL BECOME WLY LATER IN THE DAY AS THE NEXT COLD
FRONT APPROACHES FROM THE W. EXPECT A DRY DAY WITH HIGHS IN THE
MID TO UPPER 50S...WARMEST ACROSS SE GA TOWARD DARIEN.
MONDAY NIGHT...THE FORECAST BECOMES MORE TRICKY THIS PERIOD AS THE
COLD FRONT WILL SHIFT THROUGH THE AREA BRINGING COLDER AIR BACK
INTO THE AREA. MEANWHILE...A STRONG SHORTWAVE TROUGH IS EXPECTED
TO BE DROPPING SE TOWARD THE AREA WHICH COULD ADD JUST ENOUGH
LIFT TO PRODUCE SOME LIGHT RAIN INITIALLY AND THEN SOME LIGHT
SNOW. THUS...HAVE INTRODUCED SLIGHT CHANCE POPS FOR MAINLY
COLLETON COUNTY N AND E...INCLUDING THE CHARLESTON TRI-COUNTY
AREA. DO NOT ANTICIPATE ANY SNOW ACCUMULATION AT THIS POINT BUT
WILL CONTINUE TO MONITOR AS A WINTER WEATHER ADVISORY MAY BE
REQUIRED AT A LATER TIME. THIS POTENTIAL WILL BE ADDED TO THE
HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY...AN EXTREMELY INTERESTING DAY WEATHERWISE...WITH THE
POTENTIAL FOR LIGHT WINTER PRECIPITATION. LONG WAVE TROUGH IN THE
EAST BECOMES FURTHER AMPLIFIED AS STRONG SHORT WAVE DIVES INTO THE
BASE OF THE TROUGH ON TUESDAY. THIS RESULTS IN A SURFACE LOW PRES
SYSTEM DEVELOPING ALONG THE PREVIOUS COLD FRONT JUST EAST OF THE SC
AND NC COASTS EARLY TUESDAY...BEFORE IT LIFTS QUICKLY OFF TO THE NE
DURING THE DAY. COLD AIR ON THE BACK SIDE OF THE LOW WILL FILTER
INTO THE REGION AND RESULT IN AT LEAST A SMALL CHANCE OF SNOW
SHOWERS. HOWEVER...GIVEN THE STRENGTH OF THE UPPER SHORT
WAVE...UPPER LEVEL JET...STEADY HEIGHTS FALLS...Q VECTOR CONVERGENCE
AT BOTH 700-500 MB AND 500-300 MB LEVELS...DECENT OMEGA FIELDS AND
FRONTOGENESIS ACROSS THE AREA WE MIGHT NEED TO CONSIDER SOME
ACCUMULATING SNOWFALL...ESPECIALLY OVER BERKELEY...CHARLESTON...
DORCHESTER AND COLLETON COUNTIES. HOWEVER...THE MAIN DRAWBACK IS
THAT MOISTURE IS VERY SPARSE WITH PWATS LESS THAN 1/2 INCH...AND
THERE IS CONSIDERABLE DRY AIR IN ALL OF THE VERTICAL EXCEPT THE
BOUNDARY LAYER. FOR NOW WE HAVE ADDED MENTION OF SNOW SHOWERS TO THE
FORECAST FIGURING THAT TEMPS WILL GENERALLY BE ABOVE FREEZING AND
WITH LIMITED MOISTURE THAT NO ACCUMULATION WILL OCCUR.
HOWEVER...GIVEN THE STRENGTH OF THE DYNAMICS AS MENTIONED ABOVE...WE
MAY NEED TO CONSIDER A WINTER WEATHER ADVISORY AT A LATER TIME
SHOULD SMALL ACCUMULATIONS INDEED OCCUR. WE WILL MENTION THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK. TEMPS WILL HAVE A HARD
TIME RISING MUCH ABOVE THE LOWER AND MIDDLE 40S DURING TUESDAY...WITH
COLD AIR ADVECTION IN THE MORNING AND PARTLY TO MOSTLY CLOUDY SKIES.
TUESDAY NIGHT...STRONGER COLD AIR ADVECTION DEVELOPS IN WAKE OF THE
STRONG SHORT WAVE MOVING THROUGH THE AREA TUESDAY EVENING WITH
CLEARING SKIES. COLD NORTHERLY FLOW OF AIR WILL PLUNGE TEMPS DOWN
INTO THE UPPER TEENS AND LOWER 20S WELL INLAND BY WEDNESDAY
MORNING...AND WITH THE NW TO NORTH FLOW...EVEN COASTAL COMMUNITIES
WILL SEE A HARD FREEZE AS TEMPS BOTTOM OUT IN THE MID AND UPPER 20S.
ALTHOUGH THERE IS NO RISK OF WINTER PRECIP... AS THE AIR MASS DRIES
OUT FURTHER...THE COMBINATION OF THESE COLD TEMPS AND WINDS OF 5 TO
15 MPH THROUGH THE NIGHT WILL RESULT IN WIND CHILLS DOWN BETWEEN 10
AND 15 DEGREES LATER TUESDAY NIGHT...WITH EVEN A FEW READINGS IN THE
SINGLE DIGITS. A WIND CHILL ADVISORY MAY BE REQUIRED AS A
RESULT...AND WE WILL ADD MENTION TO THE HAZARDOUS WEATHER
OUTLOOK.
WEDNESDAY...A DRY NW FLOW ALOFT AND HIGH PRES BUILDING EASTWARD ALONG
THE NORTHERN GULF COAST WILL RESULT IN A SUNNY BUT COLD DAY ACROSS
THE FORECAST AREA. GIVEN THE COLD START TO THE DAY OUR TEMPS MAY BE
OPTIMISTIC REACHING THE MID AND UPPER 40S...BUT THIS IS COOLER THAN
THE PREVIOUS FORECAST...SO PERHAPS A TREND IN THE RIGHT DIRECTION
AS THICKNESS SUPPORTS ONLY LOWER AND MID 40S.
THURSDAY...HIGH PRES ACROSS THE GULF SHIFTS EAST ACROSS FLORIDA AND
EVENTUALLY INTO THE SW ATLC...ALLOWING FOR A SLIGHTLY WARMER WSW
SYNOPTIC FLOW TO DEVELOP. THIS ALONG WITH A DRY WNW FLOW ALOFT WILL
RESULT IN A GOOD DEAL OF SUNSHINE AND A WARMER DAY...WITH MOST TEMPS
BACK INTO THE 50S BY AFTERNOON.
FRIDAY...CONTINUED WARMING WITH ZONAL FLOW ALOFT AND THE AREA IS ON
THE NW SIDE OF THE ATLC RIDGE EXTENDING WEST ACROSS FLORIDA.
THICKNESS VALUES SUPPORT HIGHS NEAR OR EVEN SLIGHTLY ABOVE NORMAL.
SATURDAY AND SUNDAY...STILL SOME TIMING CONCERNS REGARDING THE NEXT
COLD FRONT...AS IT BECOMES PARALLEL TO THE FLOW ALOFT...SO IT MAY BE
A SLOW PROCESS IN WAITING FOR IT TO APPROACH AND EVENTUALLY MOVE
THROUGH THE AREA. WARMER WEATHER WILL OCCUR AHEAD OF THE FRONT.
&&
.AVIATION /06Z MONDAY THROUGH FRIDAY/...
DENSE FOG WILL PLAGUE THE TERMINALS FOR SEVERAL MORE HOURS UNTIL
DRIER AIR WORKS IN FROM THE WEST. VISIBILITIES HAVE TEMPORARILY
IMPROVED AT KSAV WHERE A BAND OF MID-LVL CLOUDINESS IS SKIRTING
THROUGH. EXPECT VISIBILITIES TO CRASH BY 08Z AGAIN AS THE CLOUDS
MOVE OFF TO THE NORTHEAST. THERE IS A POSSIBILITY THAT
VISIBILITIES MAY IMPROVE QUICKER THAN 12Z...ESPECIALLY IF THE
DRIER AIR TO THE WEST WORKS IN QUICKER THAN EXPECTED. AMENDMENTS
WILL MOST CERTAINLY BE ISSUED THROUGHOUT THE EARLY MORNING. EXPECT
VFR CONDITIONS TO PREVAIL BY 14Z WITH GUSTY WINDS POSSIBLE BY LATE
MORNING.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
PER SUNDAY EVENING TRENDS...DISCONTINUED THE SMALL CRAFT ADVISORY
FOR AMZ350. WAKE OF A WEAK COLD FROPA OVERNIGHT...WINDS/SEAS
WITHIN NEARSHORE WATERS SHOULD REMAIN BELOW SCA THRESHOLDS.
MAINTAINED THE ONGOING SCA FOR AMZ374 WITHOUT CHANGE...AS ELEVATED
WINDS/SEAS WILL PERSIST THERE.
MONDAY THROUGH MONDAY NIGHT...WSW WINDS MON MORNING WILL TURN W
THROUGH THE DAY AND INCREASE AS ANOTHER COLD FRONT APPROACHES
FROM THE W. WINDS MAY BRIEFLY GET UP TO SMALL CRAFT ADVISORY
CRITERIA OVER THE NEARSHORE WATERS...ESPECIALLY N OF EDISTO BEACH
BEYOND 10 NM FROM SHORE. THE ADVISORY FOR THE GA WATERS BEYOND 20
NM FROM SHORE WILL REMAIN IN EFFECT THROUGH THE PERIOD DUE TO A
COMBINATION OF WINDS/SEAS...ALTHOUGH WINDS WILL LIKELY DROP BELOW
ADVISORY LEVELS FOR A PERIOD LATE MON AFTERNOON.
TUESDAY AND TUESDAY NIGHT...COLD AIR ADVECTION IN WAKE OF THE NEXT
COLD FRONT ENDS TUESDAY MORNING AS LOW PRES ALONG THE FRONT OVER THE
GULF STREAM WATERS LIFTS NE. THIS ALLOWS FOR A SLIGHT DECREASE IN
WINDS AND SEAS BY AFTERNOON HOWEVER...THIS IS ONLY TEMPORARY AS
COLD AIR ADVECTION INCREASES AGAIN TUESDAY NIGHT IN WAKE OF A
VIGOROUS SHORT WAVE AND SURFACE COLD FRONT THAT MOVES
THROUGH...RESULTING IN AN INCREASE IN BOTH WINDS AND SEAS ONCE
AGAIN. SCA CONDITIONS APPEAR MOST LIKELY ACROSS THE OUTER GA WATERS
BOTH TUESDAY AND TUESDAY NIGHT...AND MARGINAL SCA/S ARE POSSIBLE
ELSEWHERE ACROSS THE MARINE AREA IN WAKE OF THE SHORT WAVE FOR
TUESDAY NIGHT. THE OFFSHORE FETCH WILL LIMIT THE HEIGHT OF THE SEAS
NEAR THE COAST...BUT SEAS WILL REACH AT LEAST TO 6-7 FT ON THE OUTER
GA WATERS DURING THIS TIME. IT IS WORTH NOTING THAT GEOSTROPHIC WIND
FIELDS AT 1000 MB REACH AS HIGH AS 35 KT TUESDAY NIGHT ACROSS
AMZ374. WITH EXCELLENT MIXING WE COULD BE LOOKING AT MARGINAL GALES
IF THESE SPEEDS COME TO BE.
WE WILL SEE A FEW RAIN AND SNOW SHOWERS ACROSS THE SC COASTAL
WATERS TUESDAY MORNING AS COLDER AIR FUNNELS INTO THE REGION.
WEDNESDAY AND WEDNESDAY NIGHT...HIGH PRES BUILDS EAST ALONG THE
NORTHERN GULF OF MEXICO WITH A MORE ANTICYCLONIC FLOW ACROSS THE
MARINE COMMUNITY TO RESULT. THAT ALONG WITH AN END TO THE COLD AIR
ADVECTION WILL CAUSE A DECREASE IN WINDS OF AT LEAST 5-10 KT...WHICH
IN TURN WILL ALLOW FOR SEAS TO SLOWLY COME DOWN A FOOT OR TWO. ANY
SCA CONDITIONS DURING THIS TIME APPEARS MOST FAVORABLE ACROSS THE
OUTER GA WATERS SINCE THE SEAS WILL BE SLOW IN SUBSIDING.
THURSDAY AND FRIDAY...HIGH PRES ACROSS FLORIDA STRETCHES EASTWARD
INTO THE ATLC LATE IN THE WEEK. THE NEXT UPSTREAM COLD FRONT REMAINS
FAR TO THE WEST AND NW DURING THIS TIME...KEEPING A MODERATE SW TO
WEST FLOW ACROSS THE LOCAL WATERS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
GAZ087-088-099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
SCZ040-042>045-047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
DENSE FOG ADVISORY UNTIL 5 AM EST EARLY THIS MORNING FOR
AMZ330.
&&
$$
000
FXUS62 KCHS 190335
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1035 PM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE OFFSHORE OVERNIGHT. A SECONDARY COLD FRONT
TO PUSH THROUGH LATE MONDAY INTO TUESDAY. LOW PRESSURE ALONG A
COLD FRONT OFF THE CAROLINAS TUESDAY MORNING WILL PULL AWAY TO THE
NE. A TRAILING COLD FRONT WILL PUSH EAST OF THE AREA LATE IN THE
DAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH LATE IN THE
WEEK...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
LATE SUNDAY EVENING...LINGERING RAIN/SHOWERS LINGERED OVER EXTREME
SOUTHERN COUNTIES...AND HAD OTHERWISE PUSHED INTO COASTAL WATERS.
IN THE WAKE OF THE WIDESPREAD RAIN EVENT...CLEARING SKIES AND A
WEAK SURFACE PRESSURE GRADIENT/LIGHT WINDS HAD CREATED CONDITIONS
IDEAL FOR DENSE FOG ACROSS THE REGION. EXPECT COVERAGE OF DENSE
FOG TO EXPAND FOR A TIME OVERNIGHT...AND DENSE FOG SHOULD IMPACT
AT LEAST PORTIONS OF THE ENTIRE REGION. THUS...ISSUED A DENSE FOG
ADVISORY FOR ALL AREAS.
ENDED THE ADVISORY AT 5 AM...AS UPSTREAM DRIER AIR MAY SPREAD INTO
THE REGION AND MAY MITIGATE THE THREAT FOR DENSE FOG BEFORE
MIDNIGHT. HOWEVER...THE MID SHIFT MAY OPT TO EXTEND THE ADVISORY
PAST DAYBREAK IF THE EXPECTED DRYING FAILS TO DEVELOP.
FURTHER...THERE IS A SLIGHT CHANCE THAT TEMPERATURES COULD FALL TO
AROUND FREEZING ACROSS FAR INLAND AREAS LATE...SUPPORTING ICY
PATCHES ON SOME ROADS EARLY MONDAY MORNING. THIS FORECAST
CONTINUES TO HOLD LOW TEMPERATURES JUST ABOVE FREEZING.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
MONDAY...SW FLOW WILL BECOME WLY LATER IN THE DAY AS THE NEXT COLD
FRONT APPROACHES FROM THE W. EXPECT A DRY DAY WITH HIGHS IN THE
MID TO UPPER 50S...WARMEST ACROSS SE GA TOWARD DARIEN.
MONDAY NIGHT...THE FORECAST BECOMES MORE TRICKY THIS PERIOD AS THE
COLD FRONT WILL SHIFT THROUGH THE AREA BRINGING COLDER AIR BACK
INTO THE AREA. MEANWHILE...A STRONG SHORTWAVE TROUGH IS EXPECTED
TO BE DROPPING SE TOWARD THE AREA WHICH COULD ADD JUST ENOUGH
LIFT TO PRODUCE SOME LIGHT RAIN INITIALLY AND THEN SOME LIGHT
SNOW. THUS...HAVE INTRODUCED SLIGHT CHANCE POPS FOR MAINLY
COLLETON COUNTY N AND E...INCLUDING THE CHARLESTON TRI-COUNTY
AREA. DO NOT ANTICIPATE ANY SNOW ACCUMULATION AT THIS POINT BUT
WILL CONTINUE TO MONITOR AS A WINTER WEATHER ADVISORY MAY BE
REQUIRED AT A LATER TIME. THIS POTENTIAL WILL BE ADDED TO THE
HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY...AN EXTREMELY INTERESTING DAY WEATHERWISE...WITH THE
POTENTIAL FOR LIGHT WINTER PRECIPITATION. LONG WAVE TROUGH IN THE
EAST BECOMES FURTHER AMPLIFIED AS STRONG SHORT WAVE DIVES INTO THE
BASE OF THE TROUGH ON TUESDAY. THIS RESULTS IN A SURFACE LOW PRES
SYSTEM DEVELOPING ALONG THE PREVIOUS COLD FRONT JUST EAST OF THE SC
AND NC COASTS EARLY TUESDAY...BEFORE IT LIFTS QUICKLY OFF TO THE NE
DURING THE DAY. COLD AIR ON THE BACK SIDE OF THE LOW WILL FILTER
INTO THE REGION AND RESULT IN AT LEAST A SMALL CHANCE OF SNOW
SHOWERS. HOWEVER...GIVEN THE STRENGTH OF THE UPPER SHORT
WAVE...UPPER LEVEL JET...STEADY HEIGHTS FALLS...Q VECTOR CONVERGENCE
AT BOTH 700-500 MB AND 500-300 MB LEVELS...DECENT OMEGA FIELDS AND
FRONTOGENESIS ACROSS THE AREA WE MIGHT NEED TO CONSIDER SOME
ACCUMULATING SNOWFALL...ESPECIALLY OVER BERKELEY...CHARLESTON...
DORCHESTER AND COLLETON COUNTIES. HOWEVER...THE MAIN DRAWBACK IS
THAT MOISTURE IS VERY SPARSE WITH PWATS LESS THAN 1/2 INCH...AND
THERE IS CONSIDERABLE DRY AIR IN ALL OF THE VERTICAL EXCEPT THE
BOUNDARY LAYER. FOR NOW WE HAVE ADDED MENTION OF SNOW SHOWERS TO THE
FORECAST FIGURING THAT TEMPS WILL GENERALLY BE ABOVE FREEZING AND
WITH LIMITED MOISTURE THAT NO ACCUMULATION WILL OCCUR.
HOWEVER...GIVEN THE STRENGTH OF THE DYNAMICS AS MENTIONED ABOVE...WE
MAY NEED TO CONSIDER A WINTER WEATHER ADVISORY AT A LATER TIME
SHOULD SMALL ACCUMULATIONS INDEED OCCUR. WE WILL MENTION THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK. TEMPS WILL HAVE A HARD
TIME RISING MUCH ABOVE THE LOWER AND MIDDLE 40S DURING TUESDAY...WITH
COLD AIR ADVECTION IN THE MORNING AND PARTLY TO MOSTLY CLOUDY SKIES.
TUESDAY NIGHT...STRONGER COLD AIR ADVECTION DEVELOPS IN WAKE OF THE
STRONG SHORT WAVE MOVING THROUGH THE AREA TUESDAY EVENING WITH
CLEARING SKIES. COLD NORTHERLY FLOW OF AIR WILL PLUNGE TEMPS DOWN
INTO THE UPPER TEENS AND LOWER 20S WELL INLAND BY WEDNESDAY
MORNING...AND WITH THE NW TO NORTH FLOW...EVEN COASTAL COMMUNITIES
WILL SEE A HARD FREEZE AS TEMPS BOTTOM OUT IN THE MID AND UPPER 20S.
ALTHOUGH THERE IS NO RISK OF WINTER PRECIP... AS THE AIR MASS DRIES
OUT FURTHER...THE COMBINATION OF THESE COLD TEMPS AND WINDS OF 5 TO
15 MPH THROUGH THE NIGHT WILL RESULT IN WIND CHILLS DOWN BETWEEN 10
AND 15 DEGREES LATER TUESDAY NIGHT...WITH EVEN A FEW READINGS IN THE
SINGLE DIGITS. A WIND CHILL ADVISORY MAY BE REQUIRED AS A
RESULT...AND WE WILL ADD MENTION TO THE HAZARDOUS WEATHER
OUTLOOK.
WEDNESDAY...A DRY NW FLOW ALOFT AND HIGH PRES BUILDING EASTWARD ALONG
THE NORTHERN GULF COAST WILL RESULT IN A SUNNY BUT COLD DAY ACROSS
THE FORECAST AREA. GIVEN THE COLD START TO THE DAY OUR TEMPS MAY BE
OPTIMISTIC REACHING THE MID AND UPPER 40S...BUT THIS IS COOLER THAN
THE PREVIOUS FORECAST...SO PERHAPS A TREND IN THE RIGHT DIRECTION
AS THICKNESS SUPPORTS ONLY LOWER AND MID 40S.
THURSDAY...HIGH PRES ACROSS THE GULF SHIFTS EAST ACROSS FLORIDA AND
EVENTUALLY INTO THE SW ATLC...ALLOWING FOR A SLIGHTLY WARMER WSW
SYNOPTIC FLOW TO DEVELOP. THIS ALONG WITH A DRY WNW FLOW ALOFT WILL
RESULT IN A GOOD DEAL OF SUNSHINE AND A WARMER DAY...WITH MOST TEMPS
BACK INTO THE 50S BY AFTERNOON.
FRIDAY...CONTINUED WARMING WITH ZONAL FLOW ALOFT AND THE AREA IS ON
THE NW SIDE OF THE ATLC RIDGE EXTENDING WEST ACROSS FLORIDA.
THICKNESS VALUES SUPPORT HIGHS NEAR OR EVEN SLIGHTLY ABOVE NORMAL.
SATURDAY AND SUNDAY...STILL SOME TIMING CONCERNS REGARDING THE NEXT
COLD FRONT...AS IT BECOMES PARALLEL TO THE FLOW ALOFT...SO IT MAY BE
A SLOW PROCESS IN WAITING FOR IT TO APPROACH AND EVENTUALLY MOVE
THROUGH THE AREA. WARMER WEATHER WILL OCCUR AHEAD OF THE FRONT.
&&
.AVIATION /04Z MONDAY THROUGH FRIDAY/...
THE COLD FRONT WILL PASS THROUGH THE AREA THIS EVENING AND THE
LIGHT RAIN WILL DIMINISH WITHIN THE NEXT HOUR AT THE KCHS
AIRPORT. IN THE IMMEDIATE WAKE OF THE FRONT...WINDS WILL DECOUPLE
AND LOW LEVEL MOISTURE WILL STILL BE IN PLACE IN WHICH FOG/LOW
STRATUS IS EXPECTED TO DEVELOP FOR A FEW HOURS EARLY TONIGHT. HAVE
INTRODUCED A TEMPO OF IFR CEILINGS AND VISIBILITIES FROM 02Z-06Z.
WITH DRY AIR LAGGING IN BEHIND THE FRONT...EXPECT VFR CONDITIONS
TO APPEAR BY DAYBREAK MONDAY. WINDS WILL BECOME GUSTY BY LATE
MORNING MONDAY AT BOTH TAF SITES.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
PER SUNDAY EVENING TRENDS...DISCONTINUED THE SMALL CRAFT ADVISORY
FOR AMZ350. WAKE OF A WEAK COLD FROPA OVERNIGHT...WINDS/SEAS
WITHIN NEARSHORE WATERS SHOULD REMAIN BELOW SCA THRESHOLDS.
MAINTAINED THE ONGOING SCA FOR AMZ374 WITHOUT CHANGE...AS ELEVATED
WINDS/SEAS WILL PERSIST THERE.
MONDAY THROUGH MONDAY NIGHT...WSW WINDS MON MORNING WILL TURN W
THROUGH THE DAY AND INCREASE AS ANOTHER COLD FRONT APPROACHES
FROM THE W. WINDS MAY BRIEFLY GET UP TO SMALL CRAFT ADVISORY
CRITERIA OVER THE NEARSHORE WATERS...ESPECIALLY N OF EDISTO BEACH
BEYOND 10 NM FROM SHORE. THE ADVISORY FOR THE GA WATERS BEYOND 20
NM FROM SHORE WILL REMAIN IN EFFECT THROUGH THE PERIOD DUE TO A
COMBINATION OF WINDS/SEAS...ALTHOUGH WINDS WILL LIKELY DROP BELOW
ADVISORY LEVELS FOR A PERIOD LATE MON AFTERNOON.
TUESDAY AND TUESDAY NIGHT...COLD AIR ADVECTION IN WAKE OF THE NEXT
COLD FRONT ENDS TUESDAY MORNING AS LOW PRES ALONG THE FRONT OVER THE
GULF STREAM WATERS LIFTS NE. THIS ALLOWS FOR A SLIGHT DECREASE IN
WINDS AND SEAS BY AFTERNOON HOWEVER...THIS IS ONLY TEMPORARY AS
COLD AIR ADVECTION INCREASES AGAIN TUESDAY NIGHT IN WAKE OF A
VIGOROUS SHORT WAVE AND SURFACE COLD FRONT THAT MOVES
THROUGH...RESULTING IN AN INCREASE IN BOTH WINDS AND SEAS ONCE
AGAIN. SCA CONDITIONS APPEAR MOST LIKELY ACROSS THE OUTER GA WATERS
BOTH TUESDAY AND TUESDAY NIGHT...AND MARGINAL SCA/S ARE POSSIBLE
ELSEWHERE ACROSS THE MARINE AREA IN WAKE OF THE SHORT WAVE FOR
TUESDAY NIGHT. THE OFFSHORE FETCH WILL LIMIT THE HEIGHT OF THE SEAS
NEAR THE COAST...BUT SEAS WILL REACH AT LEAST TO 6-7 FT ON THE OUTER
GA WATERS DURING THIS TIME. IT IS WORTH NOTING THAT GEOSTROPHIC WIND
FIELDS AT 1000 MB REACH AS HIGH AS 35 KT TUESDAY NIGHT ACROSS
AMZ374. WITH EXCELLENT MIXING WE COULD BE LOOKING AT MARGINAL GALES
IF THESE SPEEDS COME TO BE.
WE WILL SEE A FEW RAIN AND SNOW SHOWERS ACROSS THE SC COASTAL
WATERS TUESDAY MORNING AS COLDER AIR FUNNELS INTO THE REGION.
WEDNESDAY AND WEDNESDAY NIGHT...HIGH PRES BUILDS EAST ALONG THE
NORTHERN GULF OF MEXICO WITH A MORE ANTICYCLONIC FLOW ACROSS THE
MARINE COMMUNITY TO RESULT. THAT ALONG WITH AN END TO THE COLD AIR
ADVECTION WILL CAUSE A DECREASE IN WINDS OF AT LEAST 5-10 KT...WHICH
IN TURN WILL ALLOW FOR SEAS TO SLOWLY COME DOWN A FOOT OR TWO. ANY
SCA CONDITIONS DURING THIS TIME APPEARS MOST FAVORABLE ACROSS THE
OUTER GA WATERS SINCE THE SEAS WILL BE SLOW IN SUBSIDING.
THURSDAY AND FRIDAY...HIGH PRES ACROSS FLORIDA STRETCHES EASTWARD
INTO THE ATLC LATE IN THE WEEK. THE NEXT UPSTREAM COLD FRONT REMAINS
FAR TO THE WEST AND NW DURING THIS TIME...KEEPING A MODERATE SW TO
WEST FLOW ACROSS THE LOCAL WATERS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 5 AM EST MONDAY FOR GAZ087-088-
099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 5 AM EST MONDAY FOR SCZ040-042>045-
047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
DENSE FOG ADVISORY UNTIL 5 AM EST MONDAY FOR AMZ330.
&&
$$
000
FXUS62 KCHS 190242
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
942 PM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL MOVE OFFSHORE OVERNIGHT. A SECONDARY COLD FRONT
TO PUSH THROUGH LATE MONDAY INTO TUESDAY. LOW PRESSURE ALONG A
COLD FRONT OFF THE CAROLINAS TUESDAY MORNING WILL PULL AWAY TO THE
NE. A TRAILING COLD FRONT WILL PUSH EAST OF THE AREA LATE IN THE
DAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH LATE IN THE
WEEK...BEFORE THE NEXT COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
LATE SUNDAY EVENING...LINGERING RAIN/SHOWERS LINGERED OVER EXTREME
SOUTHERN COUNTIES...AND HAD OTHERWISE PUSHED INTO COASTAL WATERS.
IN THE WAKE OF THE WIDESPREAD RAIN EVENT...CLEARING SKIES AND A
WEAK SURFACE PRESSURE GRADIENT/LIGHT WINDS HAD CREATED CONDITIONS
IDEAL FOR DENSE FOG ACROSS THE REGION. EXPECT COVERAGE OF DENSE
FOG TO EXPAND FOR A TIME OVERNIGHT...AND DENSE FOG SHOULD IMPACT
AT LEAST PORTIONS OF THE ENTIRE REGION. THUS...ISSUED A DENSE FOG
ADVISORY FOR ALL AREAS.
ENDED THE ADVISORY AT 5 AM...AS UPSTREAM DRIER AIR MAY SPREAD INTO
THE REGION AND MAY MITIGATE THE THREAT FOR DENSE FOG BEFORE
MIDNIGHT. HOWEVER...THE MID SHIFT MAY OPT TO EXTEND THE ADVISORY
PAST DAYBREAK IF THE EXPECTED DRYING FAILS TO DEVELOP.
FURTHER...THERE IS A SLIGHT CHANCE THAT TEMPERATURES COULD FALL TO
AROUND FREEZING ACROSS FAR INLAND AREAS LATE...SUPPORTING ICY
PATCHES ON SOME ROADS EARLY MONDAY MORNING. THIS FORECAST
CONTINUES TO HOLD LOW TEMPERATURES JUST ABOVE FREEZING.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
MONDAY...SW FLOW WILL BECOME WLY LATER IN THE DAY AS THE NEXT COLD
FRONT APPROACHES FROM THE W. EXPECT A DRY DAY WITH HIGHS IN THE
MID TO UPPER 50S...WARMEST ACROSS SE GA TOWARD DARIEN.
MONDAY NIGHT...THE FORECAST BECOMES MORE TRICKY THIS PERIOD AS THE
COLD FRONT WILL SHIFT THROUGH THE AREA BRINGING COLDER AIR BACK
INTO THE AREA. MEANWHILE...A STRONG SHORTWAVE TROUGH IS EXPECTED
TO BE DROPPING SE TOWARD THE AREA WHICH COULD ADD JUST ENOUGH
LIFT TO PRODUCE SOME LIGHT RAIN INITIALLY AND THEN SOME LIGHT
SNOW. THUS...HAVE INTRODUCED SLIGHT CHANCE POPS FOR MAINLY
COLLETON COUNTY N AND E...INCLUDING THE CHARLESTON TRI-COUNTY
AREA. DO NOT ANTICIPATE ANY SNOW ACCUMULATION AT THIS POINT BUT
WILL CONTINUE TO MONITOR AS A WINTER WEATHER ADVISORY MAY BE
REQUIRED AT A LATER TIME. THIS POTENTIAL WILL BE ADDED TO THE
HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY...AN EXTREMELY INTERESTING DAY WEATHERWISE...WITH THE
POTENTIAL FOR LIGHT WINTER PRECIPITATION. LONG WAVE TROUGH IN THE
EAST BECOMES FURTHER AMPLIFIED AS STRONG SHORT WAVE DIVES INTO THE
BASE OF THE TROUGH ON TUESDAY. THIS RESULTS IN A SURFACE LOW PRES
SYSTEM DEVELOPING ALONG THE PREVIOUS COLD FRONT JUST EAST OF THE SC
AND NC COASTS EARLY TUESDAY...BEFORE IT LIFTS QUICKLY OFF TO THE NE
DURING THE DAY. COLD AIR ON THE BACK SIDE OF THE LOW WILL FILTER
INTO THE REGION AND RESULT IN AT LEAST A SMALL CHANCE OF SNOW
SHOWERS. HOWEVER...GIVEN THE STRENGTH OF THE UPPER SHORT
WAVE...UPPER LEVEL JET...STEADY HEIGHTS FALLS...Q VECTOR CONVERGENCE
AT BOTH 700-500 MB AND 500-300 MB LEVELS...DECENT OMEGA FIELDS AND
FRONTOGENESIS ACROSS THE AREA WE MIGHT NEED TO CONSIDER SOME
ACCUMULATING SNOWFALL...ESPECIALLY OVER BERKELEY...CHARLESTON...
DORCHESTER AND COLLETON COUNTIES. HOWEVER...THE MAIN DRAWBACK IS
THAT MOISTURE IS VERY SPARSE WITH PWATS LESS THAN 1/2 INCH...AND
THERE IS CONSIDERABLE DRY AIR IN ALL OF THE VERTICAL EXCEPT THE
BOUNDARY LAYER. FOR NOW WE HAVE ADDED MENTION OF SNOW SHOWERS TO THE
FORECAST FIGURING THAT TEMPS WILL GENERALLY BE ABOVE FREEZING AND
WITH LIMITED MOISTURE THAT NO ACCUMULATION WILL OCCUR.
HOWEVER...GIVEN THE STRENGTH OF THE DYNAMICS AS MENTIONED ABOVE...WE
MAY NEED TO CONSIDER A WINTER WEATHER ADVISORY AT A LATER TIME
SHOULD SMALL ACCUMULATIONS INDEED OCCUR. WE WILL MENTION THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK. TEMPS WILL HAVE A HARD
TIME RISING MUCH ABOVE THE LOWER AND MIDDLE 40S DURING TUESDAY...WITH
COLD AIR ADVECTION IN THE MORNING AND PARTLY TO MOSTLY CLOUDY SKIES.
TUESDAY NIGHT...STRONGER COLD AIR ADVECTION DEVELOPS IN WAKE OF THE
STRONG SHORT WAVE MOVING THROUGH THE AREA TUESDAY EVENING WITH
CLEARING SKIES. COLD NORTHERLY FLOW OF AIR WILL PLUNGE TEMPS DOWN
INTO THE UPPER TEENS AND LOWER 20S WELL INLAND BY WEDNESDAY
MORNING...AND WITH THE NW TO NORTH FLOW...EVEN COASTAL COMMUNITIES
WILL SEE A HARD FREEZE AS TEMPS BOTTOM OUT IN THE MID AND UPPER 20S.
ALTHOUGH THERE IS NO RISK OF WINTER PRECIP... AS THE AIR MASS DRIES
OUT FURTHER...THE COMBINATION OF THESE COLD TEMPS AND WINDS OF 5 TO
15 MPH THROUGH THE NIGHT WILL RESULT IN WIND CHILLS DOWN BETWEEN 10
AND 15 DEGREES LATER TUESDAY NIGHT...WITH EVEN A FEW READINGS IN THE
SINGLE DIGITS. A WIND CHILL ADVISORY MAY BE REQUIRED AS A
RESULT...AND WE WILL ADD MENTION TO THE HAZARDOUS WEATHER
OUTLOOK.
WEDNESDAY...A DRY NW FLOW ALOFT AND HIGH PRES BUILDING EASTWARD ALONG
THE NORTHERN GULF COAST WILL RESULT IN A SUNNY BUT COLD DAY ACROSS
THE FORECAST AREA. GIVEN THE COLD START TO THE DAY OUR TEMPS MAY BE
OPTIMISTIC REACHING THE MID AND UPPER 40S...BUT THIS IS COOLER THAN
THE PREVIOUS FORECAST...SO PERHAPS A TREND IN THE RIGHT DIRECTION
AS THICKNESS SUPPORTS ONLY LOWER AND MID 40S.
THURSDAY...HIGH PRES ACROSS THE GULF SHIFTS EAST ACROSS FLORIDA AND
EVENTUALLY INTO THE SW ATLC...ALLOWING FOR A SLIGHTLY WARMER WSW
SYNOPTIC FLOW TO DEVELOP. THIS ALONG WITH A DRY WNW FLOW ALOFT WILL
RESULT IN A GOOD DEAL OF SUNSHINE AND A WARMER DAY...WITH MOST TEMPS
BACK INTO THE 50S BY AFTERNOON.
FRIDAY...CONTINUED WARMING WITH ZONAL FLOW ALOFT AND THE AREA IS ON
THE NW SIDE OF THE ATLC RIDGE EXTENDING WEST ACROSS FLORIDA.
THICKNESS VALUES SUPPORT HIGHS NEAR OR EVEN SLIGHTLY ABOVE NORMAL.
SATURDAY AND SUNDAY...STILL SOME TIMING CONCERNS REGARDING THE NEXT
COLD FRONT...AS IT BECOMES PARALLEL TO THE FLOW ALOFT...SO IT MAY BE
A SLOW PROCESS IN WAITING FOR IT TO APPROACH AND EVENTUALLY MOVE
THROUGH THE AREA. WARMER WEATHER WILL OCCUR AHEAD OF THE FRONT.
&&
.AVIATION /02Z MONDAY THROUGH FRIDAY/...
THE COLD FRONT WILL PASS THROUGH THE AREA THIS EVENING AND THE
LIGHT RAIN WILL DIMINISH WITHIN THE NEXT HOUR AT THE KCHS
AIRPORT. IN THE IMMEDIATE WAKE OF THE FRONT...WINDS WILL DECOUPLE
AND LOW LEVEL MOISTURE WILL STILL BE IN PLACE IN WHICH FOG/LOW
STRATUS IS EXPECTED TO DEVELOP FOR A FEW HOURS EARLY TONIGHT. HAVE
INTRODUCED A TEMPO OF IFR CEILINGS AND VISIBILITIES FROM 02Z-06Z.
WITH DRY AIR LAGGING IN BEHIND THE FRONT...EXPECT VFR CONDITIONS
TO APPEAR BY DAYBREAK MONDAY. WINDS WILL BECOME GUSTY BY LATE
MORNING MONDAY AT BOTH TAF SITES.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
PER SUNDAY EVENING TRENDS...SHOULD BE ABLE TO DISCONTINUE THE SCA
FOR AMZ350 AS SCHEDULED AT 11 PM EST. EVEN IN THE WAKE OF COLD
FROPA OVERNIGHT...WINDS/SEAS WITHIN NEARSHORE WATERS SHOULD REMAIN
BELOW SCA THRESHOLDS. MAINTAINED THE ONGOING SCA FOR AMZ374
WITHOUT CHANGE...AS ELEVATED WINDS/SEAS WILL PERSIST THERE.
MONDAY THROUGH MONDAY NIGHT...WSW WINDS MON MORNING WILL TURN W
THROUGH THE DAY AND INCREASE AS ANOTHER COLD FRONT APPROACHES
FROM THE W. WINDS MAY BRIEFLY GET UP TO SMALL CRAFT ADVISORY
CRITERIA OVER THE NEARSHORE WATERS...ESPECIALLY N OF EDISTO BEACH
BEYOND 10 NM FROM SHORE. THE ADVISORY FOR THE GA WATERS BEYOND 20
NM FROM SHORE WILL REMAIN IN EFFECT THROUGH THE PERIOD DUE TO A
COMBINATION OF WINDS/SEAS...ALTHOUGH WINDS WILL LIKELY DROP BELOW
ADVISORY LEVELS FOR A PERIOD LATE MON AFTERNOON.
TUESDAY AND TUESDAY NIGHT...COLD AIR ADVECTION IN WAKE OF THE NEXT
COLD FRONT ENDS TUESDAY MORNING AS LOW PRES ALONG THE FRONT OVER THE
GULF STREAM WATERS LIFTS NE. THIS ALLOWS FOR A SLIGHT DECREASE IN
WINDS AND SEAS BY AFTERNOON HOWEVER...THIS IS ONLY TEMPORARY AS
COLD AIR ADVECTION INCREASES AGAIN TUESDAY NIGHT IN WAKE OF A
VIGOROUS SHORT WAVE AND SURFACE COLD FRONT THAT MOVES
THROUGH...RESULTING IN AN INCREASE IN BOTH WINDS AND SEAS ONCE
AGAIN. SCA CONDITIONS APPEAR MOST LIKELY ACROSS THE OUTER GA WATERS
BOTH TUESDAY AND TUESDAY NIGHT...AND MARGINAL SCA/S ARE POSSIBLE
ELSEWHERE ACROSS THE MARINE AREA IN WAKE OF THE SHORT WAVE FOR
TUESDAY NIGHT. THE OFFSHORE FETCH WILL LIMIT THE HEIGHT OF THE SEAS
NEAR THE COAST...BUT SEAS WILL REACH AT LEAST TO 6-7 FT ON THE OUTER
GA WATERS DURING THIS TIME. IT IS WORTH NOTING THAT GEOSTROPHIC WIND
FIELDS AT 1000 MB REACH AS HIGH AS 35 KT TUESDAY NIGHT ACROSS
AMZ374. WITH EXCELLENT MIXING WE COULD BE LOOKING AT MARGINAL GALES
IF THESE SPEEDS COME TO BE.
WE WILL SEE A FEW RAIN AND SNOW SHOWERS ACROSS THE SC COASTAL
WATERS TUESDAY MORNING AS COLDER AIR FUNNELS INTO THE REGION.
WEDNESDAY AND WEDNESDAY NIGHT...HIGH PRES BUILDS EAST ALONG THE
NORTHERN GULF OF MEXICO WITH A MORE ANTICYCLONIC FLOW ACROSS THE
MARINE COMMUNITY TO RESULT. THAT ALONG WITH AN END TO THE COLD AIR
ADVECTION WILL CAUSE A DECREASE IN WINDS OF AT LEAST 5-10 KT...WHICH
IN TURN WILL ALLOW FOR SEAS TO SLOWLY COME DOWN A FOOT OR TWO. ANY
SCA CONDITIONS DURING THIS TIME APPEARS MOST FAVORABLE ACROSS THE
OUTER GA WATERS SINCE THE SEAS WILL BE SLOW IN SUBSIDING.
THURSDAY AND FRIDAY...HIGH PRES ACROSS FLORIDA STRETCHES EASTWARD
INTO THE ATLC LATE IN THE WEEK. THE NEXT UPSTREAM COLD FRONT REMAINS
FAR TO THE WEST AND NW DURING THIS TIME...KEEPING A MODERATE SW TO
WEST FLOW ACROSS THE LOCAL WATERS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...DENSE FOG ADVISORY UNTIL 5 AM EST MONDAY FOR GAZ087-088-
099>101-114>119-137>141.
SC...DENSE FOG ADVISORY UNTIL 5 AM EST MONDAY FOR SCZ040-042>045-
047>051.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR AMZ350.
SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
DENSE FOG ADVISORY UNTIL 5 AM EST MONDAY FOR AMZ330.
&&
$$
000
FXUS62 KCHS 190036
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
736 PM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST AND MOVE OFFSHORE THIS
EVENING WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. LOW PRESSURE ALONG A COLD FRONT OFF THE CAROLINAS
TUESDAY MORNING WILL PULL AWAY TO THE NE. A TRAILING COLD FRONT
WILL PUSH EAST OF THE AREA LATE IN THE DAY. HIGH PRES WILL THEN
BUILD INTO THE AREA THROUGH LATE IN THE WEEK...BEFORE THE NEXT
COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
RAIN SHIELD WAS POISED TO EXIT COASTAL COUNTIES OF THE FORECAST
AREA...WITH A BAND OF LOW TOPPED CONVECTION TRAILING THE STEADY
RAIN ACROSS SE GEORGIA. IN THE WAKE OF WIDESPREAD PRECIPITATION...
LOW LEVEL MOISTURE/LIGHT WINDS AHEAD OF AN APPROACHING COLD FRONT
SUPPORTED FOG/DRIZZLE...AND THIS REGIME WILL CONTINUE TO SPREAD
ACROSS THE FORECAST AREA FOR A PERIOD TONIGHT. OVERNIGHT...THE
COLD FRONT WILL USHER DRIER AIR INTO THE REGION...AND MOST/ALL
FOG/STRATUS SHOULD DISSIPATE BY DAYBREAK.
UPDATED FORECASTS TO ACCOUNT FOR THESE TRENDS...AND ADDITIONAL
UPDATES WILL BE REQUIRED AS RAIN/SHOWERS EXIT THE REGION.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
MONDAY...SW FLOW WILL BECOME WLY LATER IN THE DAY AS THE NEXT COLD
FRONT APPROACHES FROM THE W. EXPECT A DRY DAY WITH HIGHS IN THE
MID TO UPPER 50S...WARMEST ACROSS SE GA TOWARD DARIEN.
MONDAY NIGHT...THE FORECAST BECOMES MORE TRICKY THIS PERIOD AS THE
COLD FRONT WILL SHIFT THROUGH THE AREA BRINGING COLDER AIR BACK
INTO THE AREA. MEANWHILE...A STRONG SHORTWAVE TROUGH IS EXPECTED
TO BE DROPPING SE TOWARD THE AREA WHICH COULD ADD JUST ENOUGH
LIFT TO PRODUCE SOME LIGHT RAIN INITIALLY AND THEN SOME LIGHT
SNOW. THUS...HAVE INTRODUCED SLIGHT CHANCE POPS FOR MAINLY
COLLETON COUNTY N AND E...INCLUDING THE CHARLESTON TRI-COUNTY
AREA. DO NOT ANTICIPATE ANY SNOW ACCUMULATION AT THIS POINT BUT
WILL CONTINUE TO MONITOR AS A WINTER WEATHER ADVISORY MAY BE
REQUIRED AT A LATER TIME. THIS POTENTIAL WILL BE ADDED TO THE
HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY...AN EXTREMELY INTERESTING DAY WEATHERWISE...WITH THE
POTENTIAL FOR LIGHT WINTER PRECIPITATION. LONG WAVE TROUGH IN THE
EAST BECOMES FURTHER AMPLIFIED AS STRONG SHORT WAVE DIVES INTO THE
BASE OF THE TROUGH ON TUESDAY. THIS RESULTS IN A SURFACE LOW PRES
SYSTEM DEVELOPING ALONG THE PREVIOUS COLD FRONT JUST EAST OF THE SC
AND NC COASTS EARLY TUESDAY...BEFORE IT LIFTS QUICKLY OFF TO THE NE
DURING THE DAY. COLD AIR ON THE BACK SIDE OF THE LOW WILL FILTER
INTO THE REGION AND RESULT IN AT LEAST A SMALL CHANCE OF SNOW
SHOWERS. HOWEVER...GIVEN THE STRENGTH OF THE UPPER SHORT
WAVE...UPPER LEVEL JET...STEADY HEIGHTS FALLS...Q VECTOR CONVERGENCE
AT BOTH 700-500 MB AND 500-300 MB LEVELS...DECENT OMEGA FIELDS AND
FRONTOGENESIS ACROSS THE AREA WE MIGHT NEED TO CONSIDER SOME
ACCUMULATING SNOWFALL...ESPECIALLY OVER BERKELEY...CHARLESTON...
DORCHESTER AND COLLETON COUNTIES. HOWEVER...THE MAIN DRAWBACK IS
THAT MOISTURE IS VERY SPARSE WITH PWATS LESS THAN 1/2 INCH...AND
THERE IS CONSIDERABLE DRY AIR IN ALL OF THE VERTICAL EXCEPT THE
BOUNDARY LAYER. FOR NOW WE HAVE ADDED MENTION OF SNOW SHOWERS TO THE
FORECAST FIGURING THAT TEMPS WILL GENERALLY BE ABOVE FREEZING AND
WITH LIMITED MOISTURE THAT NO ACCUMULATION WILL OCCUR.
HOWEVER...GIVEN THE STRENGTH OF THE DYNAMICS AS MENTIONED ABOVE...WE
MAY NEED TO CONSIDER A WINTER WEATHER ADVISORY AT A LATER TIME
SHOULD SMALL ACCUMULATIONS INDEED OCCUR. WE WILL MENTION THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK. TEMPS WILL HAVE A HARD
TIME RISING MUCH ABOVE THE LOWER AND MIDDLE 40S DURING TUESDAY...WITH
COLD AIR ADVECTION IN THE MORNING AND PARTLY TO MOSTLY CLOUDY SKIES.
TUESDAY NIGHT...STRONGER COLD AIR ADVECTION DEVELOPS IN WAKE OF THE
STRONG SHORT WAVE MOVING THROUGH THE AREA TUESDAY EVENING WITH
CLEARING SKIES. COLD NORTHERLY FLOW OF AIR WILL PLUNGE TEMPS DOWN
INTO THE UPPER TEENS AND LOWER 20S WELL INLAND BY WEDNESDAY
MORNING...AND WITH THE NW TO NORTH FLOW...EVEN COASTAL COMMUNITIES
WILL SEE A HARD FREEZE AS TEMPS BOTTOM OUT IN THE MID AND UPPER 20S.
ALTHOUGH THERE IS NO RISK OF WINTER PRECIP... AS THE AIR MASS DRIES
OUT FURTHER...THE COMBINATION OF THESE COLD TEMPS AND WINDS OF 5 TO
15 MPH THROUGH THE NIGHT WILL RESULT IN WIND CHILLS DOWN BETWEEN 10
AND 15 DEGREES LATER TUESDAY NIGHT...WITH EVEN A FEW READINGS IN THE
SINGLE DIGITS. A WIND CHILL ADVISORY MAY BE REQUIRED AS A
RESULT...AND WE WILL ADD MENTION TO THE HAZARDOUS WEATHER
OUTLOOK.
WEDNESDAY...A DRY NW FLOW ALOFT AND HIGH PRES BUILDING EASTWARD ALONG
THE NORTHERN GULF COAST WILL RESULT IN A SUNNY BUT COLD DAY ACROSS
THE FORECAST AREA. GIVEN THE COLD START TO THE DAY OUR TEMPS MAY BE
OPTIMISTIC REACHING THE MID AND UPPER 40S...BUT THIS IS COOLER THAN
THE PREVIOUS FORECAST...SO PERHAPS A TREND IN THE RIGHT DIRECTION
AS THICKNESS SUPPORTS ONLY LOWER AND MID 40S.
THURSDAY...HIGH PRES ACROSS THE GULF SHIFTS EAST ACROSS FLORIDA AND
EVENTUALLY INTO THE SW ATLC...ALLOWING FOR A SLIGHTLY WARMER WSW
SYNOPTIC FLOW TO DEVELOP. THIS ALONG WITH A DRY WNW FLOW ALOFT WILL
RESULT IN A GOOD DEAL OF SUNSHINE AND A WARMER DAY...WITH MOST TEMPS
BACK INTO THE 50S BY AFTERNOON.
FRIDAY...CONTINUED WARMING WITH ZONAL FLOW ALOFT AND THE AREA IS ON
THE NW SIDE OF THE ATLC RIDGE EXTENDING WEST ACROSS FLORIDA.
THICKNESS VALUES SUPPORT HIGHS NEAR OR EVEN SLIGHTLY ABOVE NORMAL.
SATURDAY AND SUNDAY...STILL SOME TIMING CONCERNS REGARDING THE NEXT
COLD FRONT...AS IT BECOMES PARALLEL TO THE FLOW ALOFT...SO IT MAY BE
A SLOW PROCESS IN WAITING FOR IT TO APPROACH AND EVENTUALLY MOVE
THROUGH THE AREA. WARMER WEATHER WILL OCCUR AHEAD OF THE FRONT.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
THE COLD FRONT WILL PASS THROUGH THE AREA THIS EVENING AND THE
LIGHT RAIN WILL DIMINISH WITHIN THE NEXT HOUR AT THE KCHS
AIRPORT. IN THE IMMEDIATE WAKE OF THE FRONT...WINDS WILL DECOUPLE
AND LOW LEVEL MOISTURE WILL STILL BE IN PLACE IN WHICH FOG/LOW
STRATUS IS EXPECTED TO DEVELOP FOR A FEW HOURS EARLY TONIGHT. HAVE
INTRODUCED A TEMPO OF IFR CEILINGS AND VISIBILITIES FROM 02Z-06Z.
WITH DRY AIR LAGGING IN BEHIND THE FRONT...EXPECT VFR CONDITIONS
TO APPEAR BY DAYBREAK MONDAY. WINDS WILL BECOME GUSTY BY LATE
MORNING MONDAY AT BOTH TAF SITES.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
PER SUNDAY EVENING TRENDS...FEATURING A WEAKENING SURFACE PRESSURE
GRADIENT/SLACKENING SURFACE WINDS...DISCONTINUED SMALL CRAFT
ADVISORIES FOR AMZ352 AND AMZ354. SHOULD BE ABLE TO DISCONTINUE
THE SCA FOR AMZ350 AS SCHEDULED AT 11 PM EST. EVEN IN THE WAKE OF
COLD FROPA OVERNIGHT...WINDS/SEAS WITHIN NEARSHORE WATERS SHOULD
REMAIN BELOW SCA THRESHOLDS. MAINTAINED THE ONGOING SCA FOR AMZ374
WITHOUT CHANGE.
MONDAY THROUGH MONDAY NIGHT...WSW WINDS MON MORNING WILL TURN W
THROUGH THE DAY AND INCREASE AS ANOTHER COLD FRONT APPROACHES
FROM THE W. WINDS MAY BRIEFLY GET UP TO SMALL CRAFT ADVISORY
CRITERIA OVER THE NEARSHORE WATERS...ESPECIALLY N OF EDISTO BEACH
BEYOND 10 NM FROM SHORE. THE ADVISORY FOR THE GA WATERS BEYOND 20
NM FROM SHORE WILL REMAIN IN EFFECT THROUGH THE PERIOD DUE TO A
COMBINATION OF WINDS/SEAS...ALTHOUGH WINDS WILL LIKELY DROP BELOW
ADVISORY LEVELS FOR A PERIOD LATE MON AFTERNOON.
TUESDAY AND TUESDAY NIGHT...COLD AIR ADVECTION IN WAKE OF THE NEXT
COLD FRONT ENDS TUESDAY MORNING AS LOW PRES ALONG THE FRONT OVER THE
GULF STREAM WATERS LIFTS NE. THIS ALLOWS FOR A SLIGHT DECREASE IN
WINDS AND SEAS BY AFTERNOON HOWEVER...THIS IS ONLY TEMPORARY AS
COLD AIR ADVECTION INCREASES AGAIN TUESDAY NIGHT IN WAKE OF A
VIGOROUS SHORT WAVE AND SURFACE COLD FRONT THAT MOVES
THROUGH...RESULTING IN AN INCREASE IN BOTH WINDS AND SEAS ONCE
AGAIN. SCA CONDITIONS APPEAR MOST LIKELY ACROSS THE OUTER GA WATERS
BOTH TUESDAY AND TUESDAY NIGHT...AND MARGINAL SCA/S ARE POSSIBLE
ELSEWHERE ACROSS THE MARINE AREA IN WAKE OF THE SHORT WAVE FOR
TUESDAY NIGHT. THE OFFSHORE FETCH WILL LIMIT THE HEIGHT OF THE SEAS
NEAR THE COAST...BUT SEAS WILL REACH AT LEAST TO 6-7 FT ON THE OUTER
GA WATERS DURING THIS TIME. IT IS WORTH NOTING THAT GEOSTROPHIC WIND
FIELDS AT 1000 MB REACH AS HIGH AS 35 KT TUESDAY NIGHT ACROSS
AMZ374. WITH EXCELLENT MIXING WE COULD BE LOOKING AT MARGINAL GALES
IF THESE SPEEDS COME TO BE.
WE WILL SEE A FEW RAIN AND SNOW SHOWERS ACROSS THE SC COASTAL
WATERS TUESDAY MORNING AS COLDER AIR FUNNELS INTO THE REGION.
WEDNESDAY AND WEDNESDAY NIGHT...HIGH PRES BUILDS EAST ALONG THE
NORTHERN GULF OF MEXICO WITH A MORE ANTICYCLONIC FLOW ACROSS THE
MARINE COMMUNITY TO RESULT. THAT ALONG WITH AN END TO THE COLD AIR
ADVECTION WILL CAUSE A DECREASE IN WINDS OF AT LEAST 5-10 KT...WHICH
IN TURN WILL ALLOW FOR SEAS TO SLOWLY COME DOWN A FOOT OR TWO. ANY
SCA CONDITIONS DURING THIS TIME APPEARS MOST FAVORABLE ACROSS THE
OUTER GA WATERS SINCE THE SEAS WILL BE SLOW IN SUBSIDING.
THURSDAY AND FRIDAY...HIGH PRES ACROSS FLORIDA STRETCHES EASTWARD
INTO THE ATLC LATE IN THE WEEK. THE NEXT UPSTREAM COLD FRONT REMAINS
FAR TO THE WEST AND NW DURING THIS TIME...KEEPING A MODERATE SW TO
WEST FLOW ACROSS THE LOCAL WATERS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR AMZ350.
&&
$$
000
FXUS62 KCHS 182347
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
647 PM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST AND MOVE OFFSHORE THIS
EVENING WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. LOW PRESSURE ALONG A COLD FRONT OFF THE CAROLINAS
TUESDAY MORNING WILL PULL AWAY TO THE NE. A TRAILING COLD FRONT
WILL PUSH EAST OF THE AREA LATE IN THE DAY. HIGH PRES WILL THEN
BUILD INTO THE AREA THROUGH LATE IN THE WEEK...BEFORE THE NEXT
COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
A SHORTWAVE TROUGH ACROSS NRN AL/GA WILL SHIFT NE INTO SC AND NC
THIS EVENING PUSHING A COLD FRONT THROUGH SRN SC/SE GA BY
MIDNIGHT. A WIDESPREAD AREA OF LIGHT TO MODERATE RAIN IS MOVING
THROUGH THE AREA AND WILL CONTINUE TO PUSH NE AND OFFSHORE THIS
EVENING WITH THE FRONT. TEMPERATURES AHEAD OF THE FRONT HAVE BEEN
STUCK IN THE 40S BACK INLAND WHILE SOME BREAKS IN THE CLOUDS HAVE
LED TO TEMPERATURES PUSHING INTO THE LOWER 60S S AND E OF
SAVANNAH.
WINDS WILL VEER TO W THIS EVENING BEHIND THE INITIAL FRONT BUT
QUICKLY BACK TO THE SW TOWARD DAYBREAK AS THE FLOW RESPONDS TO
A SURFACE LOW DEVELOPING ACROSS WRN NC/VA AHEAD OF ANOTHER
SHORTWAVE TROUGH ROUNDING THE BASE OF THE LARGE UPPER TROUGH OVER
THE E COAST. LOW TEMPS WILL DEPEND LARGELY ON THE AMOUNT OF
LINGERING CLOUDS BEHIND THE INITIAL FRONT AND THEN AHEAD OF THE
SECONDARY FRONT EXTENDING FROM THE AFOREMENTIONED LOW ACROSS NC/VA.
BASICALLY TOOK A COMPROMISE BETWEEN THE COOLER GFS MOS GUIDANCE
AND WARMER MET GUIDANCE WHICH YIELDS TEMPS GENERALLY IN THE
MID/UPPER 30S WITH MID 40S ALONG THE COAST.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
MONDAY...SW FLOW WILL BECOME WLY LATER IN THE DAY AS THE NEXT COLD
FRONT APPROACHES FROM THE W. EXPECT A DRY DAY WITH HIGHS IN THE
MID TO UPPER 50S...WARMEST ACROSS SE GA TOWARD DARIEN.
MONDAY NIGHT...THE FORECAST BECOMES MORE TRICKY THIS PERIOD AS THE
COLD FRONT WILL SHIFT THROUGH THE AREA BRINGING COLDER AIR BACK
INTO THE AREA. MEANWHILE...A STRONG SHORTWAVE TROUGH IS EXPECTED
TO BE DROPPING SE TOWARD THE AREA WHICH COULD ADD JUST ENOUGH
LIFT TO PRODUCE SOME LIGHT RAIN INITIALLY AND THEN SOME LIGHT
SNOW. THUS...HAVE INTRODUCED SLIGHT CHANCE POPS FOR MAINLY
COLLETON COUNTY N AND E...INCLUDING THE CHARLESTON TRI-COUNTY
AREA. DO NOT ANTICIPATE ANY SNOW ACCUMULATION AT THIS POINT BUT
WILL CONTINUE TO MONITOR AS A WINTER WEATHER ADVISORY MAY BE
REQUIRED AT A LATER TIME. THIS POTENTIAL WILL BE ADDED TO THE
HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY...AN EXTREMELY INTERESTING DAY WEATHERWISE...WITH THE
POTENTIAL FOR LIGHT WINTER PRECIPITATION. LONG WAVE TROUGH IN THE
EAST BECOMES FURTHER AMPLIFIED AS STRONG SHORT WAVE DIVES INTO THE
BASE OF THE TROUGH ON TUESDAY. THIS RESULTS IN A SURFACE LOW PRES
SYSTEM DEVELOPING ALONG THE PREVIOUS COLD FRONT JUST EAST OF THE SC
AND NC COASTS EARLY TUESDAY...BEFORE IT LIFTS QUICKLY OFF TO THE NE
DURING THE DAY. COLD AIR ON THE BACK SIDE OF THE LOW WILL FILTER
INTO THE REGION AND RESULT IN AT LEAST A SMALL CHANCE OF SNOW
SHOWERS. HOWEVER...GIVEN THE STRENGTH OF THE UPPER SHORT
WAVE...UPPER LEVEL JET...STEADY HEIGHTS FALLS...Q VECTOR CONVERGENCE
AT BOTH 700-500 MB AND 500-300 MB LEVELS...DECENT OMEGA FIELDS AND
FRONTOGENESIS ACROSS THE AREA WE MIGHT NEED TO CONSIDER SOME
ACCUMULATING SNOWFALL...ESPECIALLY OVER BERKELEY...CHARLESTON...
DORCHESTER AND COLLETON COUNTIES. HOWEVER...THE MAIN DRAWBACK IS
THAT MOISTURE IS VERY SPARSE WITH PWATS LESS THAN 1/2 INCH...AND
THERE IS CONSIDERABLE DRY AIR IN ALL OF THE VERTICAL EXCEPT THE
BOUNDARY LAYER. FOR NOW WE HAVE ADDED MENTION OF SNOW SHOWERS TO THE
FORECAST FIGURING THAT TEMPS WILL GENERALLY BE ABOVE FREEZING AND
WITH LIMITED MOISTURE THAT NO ACCUMULATION WILL OCCUR.
HOWEVER...GIVEN THE STRENGTH OF THE DYNAMICS AS MENTIONED ABOVE...WE
MAY NEED TO CONSIDER A WINTER WEATHER ADVISORY AT A LATER TIME
SHOULD SMALL ACCUMULATIONS INDEED OCCUR. WE WILL MENTION THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK. TEMPS WILL HAVE A HARD
TIME RISING MUCH ABOVE THE LOWER AND MIDDLE 40S DURING TUESDAY...WITH
COLD AIR ADVECTION IN THE MORNING AND PARTLY TO MOSTLY CLOUDY SKIES.
TUESDAY NIGHT...STRONGER COLD AIR ADVECTION DEVELOPS IN WAKE OF THE
STRONG SHORT WAVE MOVING THROUGH THE AREA TUESDAY EVENING WITH
CLEARING SKIES. COLD NORTHERLY FLOW OF AIR WILL PLUNGE TEMPS DOWN
INTO THE UPPER TEENS AND LOWER 20S WELL INLAND BY WEDNESDAY
MORNING...AND WITH THE NW TO NORTH FLOW...EVEN COASTAL COMMUNITIES
WILL SEE A HARD FREEZE AS TEMPS BOTTOM OUT IN THE MID AND UPPER 20S.
ALTHOUGH THERE IS NO RISK OF WINTER PRECIP... AS THE AIR MASS DRIES
OUT FURTHER...THE COMBINATION OF THESE COLD TEMPS AND WINDS OF 5 TO
15 MPH THROUGH THE NIGHT WILL RESULT IN WIND CHILLS DOWN BETWEEN 10
AND 15 DEGREES LATER TUESDAY NIGHT...WITH EVEN A FEW READINGS IN THE
SINGLE DIGITS. A WIND CHILL ADVISORY MAY BE REQUIRED AS A
RESULT...AND WE WILL ADD MENTION TO THE HAZARDOUS WEATHER
OUTLOOK.
WEDNESDAY...A DRY NW FLOW ALOFT AND HIGH PRES BUILDING EASTWARD ALONG
THE NORTHERN GULF COAST WILL RESULT IN A SUNNY BUT COLD DAY ACROSS
THE FORECAST AREA. GIVEN THE COLD START TO THE DAY OUR TEMPS MAY BE
OPTIMISTIC REACHING THE MID AND UPPER 40S...BUT THIS IS COOLER THAN
THE PREVIOUS FORECAST...SO PERHAPS A TREND IN THE RIGHT DIRECTION
AS THICKNESS SUPPORTS ONLY LOWER AND MID 40S.
THURSDAY...HIGH PRES ACROSS THE GULF SHIFTS EAST ACROSS FLORIDA AND
EVENTUALLY INTO THE SW ATLC...ALLOWING FOR A SLIGHTLY WARMER WSW
SYNOPTIC FLOW TO DEVELOP. THIS ALONG WITH A DRY WNW FLOW ALOFT WILL
RESULT IN A GOOD DEAL OF SUNSHINE AND A WARMER DAY...WITH MOST TEMPS
BACK INTO THE 50S BY AFTERNOON.
FRIDAY...CONTINUED WARMING WITH ZONAL FLOW ALOFT AND THE AREA IS ON
THE NW SIDE OF THE ATLC RIDGE EXTENDING WEST ACROSS FLORIDA.
THICKNESS VALUES SUPPORT HIGHS NEAR OR EVEN SLIGHTLY ABOVE NORMAL.
SATURDAY AND SUNDAY...STILL SOME TIMING CONCERNS REGARDING THE NEXT
COLD FRONT...AS IT BECOMES PARALLEL TO THE FLOW ALOFT...SO IT MAY BE
A SLOW PROCESS IN WAITING FOR IT TO APPROACH AND EVENTUALLY MOVE
THROUGH THE AREA. WARMER WEATHER WILL OCCUR AHEAD OF THE FRONT.
&&
.AVIATION /00Z MONDAY THROUGH FRIDAY/...
THE COLD FRONT WILL PASS THROUGH THE AREA THIS EVENING AND THE
LIGHT RAIN WILL DIMINISH WITHIN THE NEXT HOUR AT THE KCHS
AIRPORT. IN THE IMMEDIATE WAKE OF THE FRONT...WINDS WILL DECOUPLE
AND LOW LEVEL MOISTURE WILL STILL BE IN PLACE IN WHICH FOG/LOW
STRATUS IS EXPECTED TO DEVELOP FOR A FEW HOURS EARLY TONIGHT. HAVE
INTRODUCED A TEMPO OF IFR CEILINGS AND VISIBILITIES FROM 02Z-06Z.
WITH DRY AIR LAGGING IN BEHIND THE FRONT...EXPECT VFR CONDITIONS
TO APPEAR BY DAYBREAK MONDAY. WINDS WILL BECOME GUSTY BY LATE
MORNING MONDAY AT BOTH TAF SITES.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
TONIGHT...WINDS ARE INCREASING ACROSS THE WATERS AHEAD OF A COLD
FRONT WHICH WILL PUSH THROUGH THE MARINE AREA THIS EVENING. SW
WINDS WILL BECOME W AND DIMINISH BEHIND THE FRONT DUE TO THE LACK
OF COLD AIR ADVECTION AND STRONG PRES GRADIENT. DECIDED TO RAISE A
SMALL CRAFT ADVISORY THROUGH THIS EVENING FOR THE SRN SC AND GA
NEARSHORE WATERS TO COVER THE SW SURGE AND RESULTING INCREASE IN
SEAS. THE ADVISORY FOR THE GA WATERS BEYOND 20 NM WILL REMAIN IN
EFFECT THROUGH THE NIGHT AS 25-30 KT WINDS AND SEAS UP TO 9 FT
ARE EXPECTED.
MONDAY THROUGH MONDAY NIGHT...WSW WINDS MON MORNING WILL TURN W
THROUGH THE DAY AND INCREASE AS ANOTHER COLD FRONT APPROACHES
FROM THE W. WINDS MAY BRIEFLY GET UP TO SMALL CRAFT ADVISORY
CRITERIA OVER THE NEARSHORE WATERS...ESPECIALLY N OF EDISTO BEACH
BEYOND 10 NM FROM SHORE. THE ADVISORY FOR THE GA WATERS BEYOND 20
NM FROM SHORE WILL REMAIN IN EFFECT THROUGH THE PERIOD DUE TO A
COMBINATION OF WINDS/SEAS...ALTHOUGH WINDS WILL LIKELY DROP BELOW
ADVISORY LEVELS FOR A PERIOD LATE MON AFTERNOON.
TUESDAY AND TUESDAY NIGHT...COLD AIR ADVECTION IN WAKE OF THE NEXT
COLD FRONT ENDS TUESDAY MORNING AS LOW PRES ALONG THE FRONT OVER THE
GULF STREAM WATERS LIFTS NE. THIS ALLOWS FOR A SLIGHT DECREASE IN
WINDS AND SEAS BY AFTERNOON HOWEVER...THIS IS ONLY TEMPORARY AS
COLD AIR ADVECTION INCREASES AGAIN TUESDAY NIGHT IN WAKE OF A
VIGOROUS SHORT WAVE AND SURFACE COLD FRONT THAT MOVES
THROUGH...RESULTING IN AN INCREASE IN BOTH WINDS AND SEAS ONCE
AGAIN. SCA CONDITIONS APPEAR MOST LIKELY ACROSS THE OUTER GA WATERS
BOTH TUESDAY AND TUESDAY NIGHT...AND MARGINAL SCA/S ARE POSSIBLE
ELSEWHERE ACROSS THE MARINE AREA IN WAKE OF THE SHORT WAVE FOR
TUESDAY NIGHT. THE OFFSHORE FETCH WILL LIMIT THE HEIGHT OF THE SEAS
NEAR THE COAST...BUT SEAS WILL REACH AT LEAST TO 6-7 FT ON THE OUTER
GA WATERS DURING THIS TIME. IT IS WORTH NOTING THAT GEOSTROPHIC WIND
FIELDS AT 1000 MB REACH AS HIGH AS 35 KT TUESDAY NIGHT ACROSS
AMZ374. WITH EXCELLENT MIXING WE COULD BE LOOKING AT MARGINAL GALES
IF THESE SPEEDS COME TO BE.
WE WILL SEE A FEW RAIN AND SNOW SHOWERS ACROSS THE SC COASTAL
WATERS TUESDAY MORNING AS COLDER AIR FUNNELS INTO THE REGION.
WEDNESDAY AND WEDNESDAY NIGHT...HIGH PRES BUILDS EAST ALONG THE
NORTHERN GULF OF MEXICO WITH A MORE ANTICYCLONIC FLOW ACROSS THE
MARINE COMMUNITY TO RESULT. THAT ALONG WITH AN END TO THE COLD AIR
ADVECTION WILL CAUSE A DECREASE IN WINDS OF AT LEAST 5-10 KT...WHICH
IN TURN WILL ALLOW FOR SEAS TO SLOWLY COME DOWN A FOOT OR TWO. ANY
SCA CONDITIONS DURING THIS TIME APPEARS MOST FAVORABLE ACROSS THE
OUTER GA WATERS SINCE THE SEAS WILL BE SLOW IN SUBSIDING.
THURSDAY AND FRIDAY...HIGH PRES ACROSS FLORIDA STRETCHES EASTWARD
INTO THE ATLC LATE IN THE WEEK. THE NEXT UPSTREAM COLD FRONT REMAINS
FAR TO THE WEST AND NW DURING THIS TIME...KEEPING A MODERATE SW TO
WEST FLOW ACROSS THE LOCAL WATERS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR AMZ350-
352-354.
SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
&&
$$
000
FXUS62 KCHS 182107
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
407 PM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST AND MOVE OFFSHORE THIS
EVENING WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. LOW PRESSURE ALONG A COLD FRONT OFF THE CAROLINAS
TUESDAY MORNING WILL PULL AWAY TO THE NE. A TRAILING COLD FRONT
WILL PUSH EAST OF THE AREA LATE IN THE DAY. HIGH PRES WILL THEN
BUILD INTO THE AREA THROUGH LATE IN THE WEEK...BEFORE THE NEXT
COLD FRONT APPROACHES DURING THE WEEKEND.
&&
.NEAR TERM /THROUGH TONIGHT/...
A SHORTWAVE TROUGH ACROSS NRN AL/GA WILL SHIFT NE INTO SC AND NC
THIS EVENING PUSHING A COLD FRONT THROUGH SRN SC/SE GA BY
MIDNIGHT. A WIDESPREAD AREA OF LIGHT TO MODERATE RAIN IS MOVING
THROUGH THE AREA AND WILL CONTINUE TO PUSH NE AND OFFSHORE THIS
EVENING WITH THE FRONT. TEMPERATURES AHEAD OF THE FRONT HAVE BEEN
STUCK IN THE 40S BACK INLAND WHILE SOME BREAKS IN THE CLOUDS HAVE
LED TO TEMPERATURES PUSHING INTO THE LOWER 60S S AND E OF
SAVANNAH.
WINDS WILL VEER TO W THIS EVENING BEHIND THE INITIAL FRONT BUT
QUICKLY BACK TO THE SW TOWARD DAYBREAK AS THE FLOW RESPONDS TO
A SURFACE LOW DEVELOPING ACROSS WRN NC/VA AHEAD OF ANOTHER
SHORTWAVE TROUGH ROUNDING THE BASE OF THE LARGE UPPER TROUGH OVER
THE E COAST. LOW TEMPS WILL DEPEND LARGELY ON THE AMOUNT OF
LINGERING CLOUDS BEHIND THE INITIAL FRONT AND THEN AHEAD OF THE
SECONDARY FRONT EXTENDING FROM THE AFOREMENTIONED LOW ACROSS NC/VA.
BASICALLY TOOK A COMPROMISE BETWEEN THE COOLER GFS MOS GUIDANCE
AND WARMER MET GUIDANCE WHICH YIELDS TEMPS GENERALLY IN THE
MID/UPPER 30S WITH MID 40S ALONG THE COAST.
&&
.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
MONDAY...SW FLOW WILL BECOME WLY LATER IN THE DAY AS THE NEXT COLD
FRONT APPROACHES FROM THE W. EXPECT A DRY DAY WITH HIGHS IN THE
MID TO UPPER 50S...WARMEST ACROSS SE GA TOWARD DARIEN.
MONDAY NIGHT...THE FORECAST BECOMES MORE TRICKY THIS PERIOD AS THE
COLD FRONT WILL SHIFT THROUGH THE AREA BRINGING COLDER AIR BACK
INTO THE AREA. MEANWHILE...A STRONG SHORTWAVE TROUGH IS EXPECTED
TO BE DROPPING SE TOWARD THE AREA WHICH COULD ADD JUST ENOUGH
LIFT TO PRODUCE SOME LIGHT RAIN INITIALLY AND THEN SOME LIGHT
SNOW. THUS...HAVE INTRODUCED SLIGHT CHANCE POPS FOR MAINLY
COLLETON COUNTY N AND E...INCLUDING THE CHARLESTON TRI-COUNTY
AREA. DO NOT ANTICIPATE ANY SNOW ACCUMULATION AT THIS POINT BUT
WILL CONTINUE TO MONITOR AS A WINTER WEATHER ADVISORY MAY BE
REQUIRED AT A LATER TIME. THIS POTENTIAL WILL BE ADDED TO THE
HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TUESDAY THROUGH SUNDAY/...
TUESDAY...AN EXTREMELY INTERESTING DAY WEATHERWISE...WITH THE
POTENTIAL FOR LIGHT WINTER PRECIPITATION. LONG WAVE TROUGH IN THE
EAST BECOMES FURTHER AMPLIFIED AS STRONG SHORT WAVE DIVES INTO THE
BASE OF THE TROUGH ON TUESDAY. THIS RESULTS IN A SURFACE LOW PRES
SYSTEM DEVELOPING ALONG THE PREVIOUS COLD FRONT JUST EAST OF THE SC
AND NC COASTS EARLY TUESDAY...BEFORE IT LIFTS QUICKLY OFF TO THE NE
DURING THE DAY. COLD AIR ON THE BACK SIDE OF THE LOW WILL FILTER
INTO THE REGION AND RESULT IN AT LEAST A SMALL CHANCE OF SNOW
SHOWERS. HOWEVER...GIVEN THE STRENGTH OF THE UPPER SHORT
WAVE...UPPER LEVEL JET...STEADY HEIGHTS FALLS...Q VECTOR CONVERGENCE
AT BOTH 700-500 MB AND 500-300 MB LEVELS...DECENT OMEGA FIELDS AND
FRONTOGENESIS ACROSS THE AREA WE MIGHT NEED TO CONSIDER SOME
ACCUMULATING SNOWFALL...ESPECIALLY OVER BERKELEY...CHARLESTON...
DORCHESTER AND COLLETON COUNTIES. HOWEVER...THE MAIN DRAWBACK IS
THAT MOISTURE IS VERY SPARSE WITH PWATS LESS THAN 1/2 INCH...AND
THERE IS CONSIDERABLE DRY AIR IN ALL OF THE VERTICAL EXCEPT THE
BOUNDARY LAYER. FOR NOW WE HAVE ADDED MENTION OF SNOW SHOWERS TO THE
FORECAST FIGURING THAT TEMPS WILL GENERALLY BE ABOVE FREEZING AND
WITH LIMITED MOISTURE THAT NO ACCUMULATION WILL OCCUR.
HOWEVER...GIVEN THE STRENGTH OF THE DYNAMICS AS MENTIONED ABOVE...WE
MAY NEED TO CONSIDER A WINTER WEATHER ADVISORY AT A LATER TIME
SHOULD SMALL ACCUMULATIONS INDEED OCCUR. WE WILL MENTION THIS
POSSIBILITY IN THE HAZARDOUS WEATHER OUTLOOK. TEMPS WILL HAVE A HARD
TIME RISING MUCH ABOVE THE LOWER AND MIDDLE 40S DURING TUESDAY...WITH
COLD AIR ADVECTION IN THE MORNING AND PARTLY TO MOSTLY CLOUDY SKIES.
TUESDAY NIGHT...STRONGER COLD AIR ADVECTION DEVELOPS IN WAKE OF THE
STRONG SHORT WAVE MOVING THROUGH THE AREA TUESDAY EVENING WITH
CLEARING SKIES. COLD NORTHERLY FLOW OF AIR WILL PLUNGE TEMPS DOWN
INTO THE UPPER TEENS AND LOWER 20S WELL INLAND BY WEDNESDAY
MORNING...AND WITH THE NW TO NORTH FLOW...EVEN COASTAL COMMUNITIES
WILL SEE A HARD FREEZE AS TEMPS BOTTOM OUT IN THE MID AND UPPER 20S.
ALTHOUGH THERE IS NO RISK OF WINTER PRECIP... AS THE AIR MASS DRIES
OUT FURTHER...THE COMBINATION OF THESE COLD TEMPS AND WINDS OF 5 TO
15 MPH THROUGH THE NIGHT WILL RESULT IN WIND CHILLS DOWN BETWEEN 10
AND 15 DEGREES LATER TUESDAY NIGHT...WITH EVEN A FEW READINGS IN THE
SINGLE DIGITS. A WIND CHILL ADVISORY MAY BE REQUIRED AS A
RESULT...AND WE WILL ADD MENTION TO THE HAZARDOUS WEATHER
OUTLOOK.
WEDNESDAY...A DRY NW FLOW ALOFT AND HIGH PRES BUILDING EASTWARD ALONG
THE NORTHERN GULF COAST WILL RESULT IN A SUNNY BUT COLD DAY ACROSS
THE FORECAST AREA. GIVEN THE COLD START TO THE DAY OUR TEMPS MAY BE
OPTIMISTIC REACHING THE MID AND UPPER 40S...BUT THIS IS COOLER THAN
THE PREVIOUS FORECAST...SO PERHAPS A TREND IN THE RIGHT DIRECTION
AS THICKNESS SUPPORTS ONLY LOWER AND MID 40S.
THURSDAY...HIGH PRES ACROSS THE GULF SHIFTS EAST ACROSS FLORIDA AND
EVENTUALLY INTO THE SW ATLC...ALLOWING FOR A SLIGHTLY WARMER WSW
SYNOPTIC FLOW TO DEVELOP. THIS ALONG WITH A DRY WNW FLOW ALOFT WILL
RESULT IN A GOOD DEAL OF SUNSHINE AND A WARMER DAY...WITH MOST TEMPS
BACK INTO THE 50S BY AFTERNOON.
FRIDAY...CONTINUED WARMING WITH ZONAL FLOW ALOFT AND THE AREA IS ON
THE NW SIDE OF THE ATLC RIDGE EXTENDING WEST ACROSS FLORIDA.
THICKNESS VALUES SUPPORT HIGHS NEAR OR EVEN SLIGHTLY ABOVE NORMAL.
SATURDAY AND SUNDAY...STILL SOME TIMING CONCERNS REGARDING THE NEXT
COLD FRONT...AS IT BECOMES PARALLEL TO THE FLOW ALOFT...SO IT MAY BE
A SLOW PROCESS IN WAITING FOR IT TO APPROACH AND EVENTUALLY MOVE
THROUGH THE AREA. WARMER WEATHER WILL OCCUR AHEAD OF THE FRONT.
&&
.AVIATION /20Z SUNDAY THROUGH FRIDAY/...
EXTENSIVE MID- LEVEL CLOUDINESS WITH VFR CIGS WILL REMAIN ACROSS
THE TERMINALS BEFORE BEGINNING TO STEADILY FALL EARLY THIS
AFTERNOON AS A LARGE SWATH OF RAINFALL APPROACHES FROM THE W. BOTH
CIGS AND VSBYS LOOK TO DROP TO MVFR THRESHOLDS BY MID
AFTERNOON...ROUGHLY AFTER 19Z... WITH POCKETS OF HEAVIER RAINFALL
TEMPORARILY DROPPING CONDITIONS EVEN LOWER. EXPECT TEMPO IFR AT
KCHS BETWEEN 18/21-19/01Z AT KCHS AND 18/22-19/02Z AT KSAV WHEN
THE HEAVIEST RAINFALL IS LIKELY. FURTHER REFINEMENTS IN BOTH
TIMING AND INTENSITY OF THE HEAVIEST RAINS WILL LIKELY BE NEEDED
AS SHORT TERM TRENDS BECOME MORE EVIDENT AND WILL CONTINUE TO
MONITOR. MAY SEE MVFR/IFR CIGS REMAIN MUCH OF THE NIGHT EVEN AFTER
THE FRONTAL PASSAGE...ESPECIALLY AT KCHS... AND SO DECIDED TO
TREND THAT WAY IN THE 18Z/18 TAFS. HOWEVER...WITH RELATIVELY LOW
CONFIDENCE AT THIS POINT...HAVE GONE NO LOWER THAN MVFR CONDS.
EXTENDED AVIATION OUTLOOK...THERE COULD BE A PERIOD OF MARGINAL MVFR
CONDITIONS WITH POSSIBLE LIGHT SNOW LATE MONDAY NIGHT INTO TUESDAY
MORNING...ESPECIALLY AT KCHS. OTHERWISE VFR WEATHER WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
TONIGHT...WINDS ARE INCREASING ACROSS THE WATERS AHEAD OF A COLD
FRONT WHICH WILL PUSH THROUGH THE MARINE AREA THIS EVENING. SW
WINDS WILL BECOME W AND DIMINISH BEHIND THE FRONT DUE TO THE LACK
OF COLD AIR ADVECTION AND STRONG PRES GRADIENT. DECIDED TO RAISE A
SMALL CRAFT ADVISORY THROUGH THIS EVENING FOR THE SRN SC AND GA
NEARSHORE WATERS TO COVER THE SW SURGE AND RESULTING INCREASE IN
SEAS. THE ADVISORY FOR THE GA WATERS BEYOND 20 NM WILL REMAIN IN
EFFECT THROUGH THE NIGHT AS 25-30 KT WINDS AND SEAS UP TO 9 FT
ARE EXPECTED.
MONDAY THROUGH MONDAY NIGHT...WSW WINDS MON MORNING WILL TURN W
THROUGH THE DAY AND INCREASE AS ANOTHER COLD FRONT APPROACHES
FROM THE W. WINDS MAY BRIEFLY GET UP TO SMALL CRAFT ADVISORY
CRITERIA OVER THE NEARSHORE WATERS...ESPECIALLY N OF EDISTO BEACH
BEYOND 10 NM FROM SHORE. THE ADVISORY FOR THE GA WATERS BEYOND 20
NM FROM SHORE WILL REMAIN IN EFFECT THROUGH THE PERIOD DUE TO A
COMBINATION OF WINDS/SEAS...ALTHOUGH WINDS WILL LIKELY DROP BELOW
ADVISORY LEVELS FOR A PERIOD LATE MON AFTERNOON.
TUESDAY AND TUESDAY NIGHT...COLD AIR ADVECTION IN WAKE OF THE NEXT
COLD FRONT ENDS TUESDAY MORNING AS LOW PRES ALONG THE FRONT OVER THE
GULF STREAM WATERS LIFTS NE. THIS ALLOWS FOR A SLIGHT DECREASE IN
WINDS AND SEAS BY AFTERNOON HOWEVER...THIS IS ONLY TEMPORARY AS
COLD AIR ADVECTION INCREASES AGAIN TUESDAY NIGHT IN WAKE OF A
VIGOROUS SHORT WAVE AND SURFACE COLD FRONT THAT MOVES
THROUGH...RESULTING IN AN INCREASE IN BOTH WINDS AND SEAS ONCE
AGAIN. SCA CONDITIONS APPEAR MOST LIKELY ACROSS THE OUTER GA WATERS
BOTH TUESDAY AND TUESDAY NIGHT...AND MARGINAL SCA/S ARE POSSIBLE
ELSEWHERE ACROSS THE MARINE AREA IN WAKE OF THE SHORT WAVE FOR
TUESDAY NIGHT. THE OFFSHORE FETCH WILL LIMIT THE HEIGHT OF THE SEAS
NEAR THE COAST...BUT SEAS WILL REACH AT LEAST TO 6-7 FT ON THE OUTER
GA WATERS DURING THIS TIME. IT IS WORTH NOTING THAT GEOSTROPHIC WIND
FIELDS AT 1000 MB REACH AS HIGH AS 35 KT TUESDAY NIGHT ACROSS
AMZ374. WITH EXCELLENT MIXING WE COULD BE LOOKING AT MARGINAL GALES
IF THESE SPEEDS COME TO BE.
WE WILL SEE A FEW RAIN AND SNOW SHOWERS ACROSS THE SC COASTAL
WATERS TUESDAY MORNING AS COLDER AIR FUNNELS INTO THE REGION.
WEDNESDAY AND WEDNESDAY NIGHT...HIGH PRES BUILDS EAST ALONG THE
NORTHERN GULF OF MEXICO WITH A MORE ANTICYCLONIC FLOW ACROSS THE
MARINE COMMUNITY TO RESULT. THAT ALONG WITH AN END TO THE COLD AIR
ADVECTION WILL CAUSE A DECREASE IN WINDS OF AT LEAST 5-10 KT...WHICH
IN TURN WILL ALLOW FOR SEAS TO SLOWLY COME DOWN A FOOT OR TWO. ANY
SCA CONDITIONS DURING THIS TIME APPEARS MOST FAVORABLE ACROSS THE
OUTER GA WATERS SINCE THE SEAS WILL BE SLOW IN SUBSIDING.
THURSDAY AND FRIDAY...HIGH PRES ACROSS FLORIDA STRETCHES EASTWARD
INTO THE ATLC LATE IN THE WEEK. THE NEXT UPSTREAM COLD FRONT REMAINS
FAR TO THE WEST AND NW DURING THIS TIME...KEEPING A MODERATE SW TO
WEST FLOW ACROSS THE LOCAL WATERS.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 11 PM EST THIS EVENING FOR AMZ350-
352-354.
SMALL CRAFT ADVISORY UNTIL 11 AM EST WEDNESDAY FOR AMZ374.
&&
$$
RJB/33
000
FXUS62 KCHS 181733
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1233 PM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AND MOVE OFFSHORE
TONIGHT WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH
THURSDAY WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A SHORTWAVE TROUGH DIGGING ACROSS NORTHERN ALABAMA WILL LIFT E
ACROSS GA/SC TODAY PUSHING A SURFACE COLD FRONT TOWARD THE AREA
AND OFF THE COAST EARLY THIS EVENING. WILL KEEP POPS IN THE
CATEGORICAL RANGE /80S- 90S/ WITH THE HIGHEST POPS ACROSS SRN SC
AS DECENT MOISTURE/LIFT ARE PROGGED TO BE OVER THE AREA. EXPECT
STORM TOTAL RAINFALL AMOUNTS OF 1/2 TO 3/4 OF AN INCH WITH LOCALLY
HIGHER AMOUNTS POSSIBLE.
PINNING DOWN HIGH TEMPERATURES TODAY WILL BE DIFFICULT AT BEST AS
MUCH DEPENDS ON THE CLOUD COVER...WHICH IS ERODING QUICKLY FROM
THE S THIS MORNING...AND THE COVERAGE/INTENSITY OF THE RAIN. THINK
NW AREAS FROM AROUND JAMESTOWN TO RIDGEVILLE TO ALLENDALE TO
SCREVEN WILL LIKELY REMAIN IN THE MID/UPPER 40S TODAY AS THOSE
AREAS ARE ALREADY SEEING RAIN. TEMPS SHOULD REACH AROUND 60
DEGREES DOWN NEAR DARIEN AS MORE BREAKS IN THE CLOUDS AND A LATER
START TO THE RAIN ARE EXPECTED THERE.
OVERALL NOT MUCH CHANGE NEEDED TO THE CURRENT FORECAST.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
SHOWERS WILL QUICKLY END FROM WEST TO EAST TONIGHT AS A COLD FRONT
MOVES OFFSHORE. TEMPERATURES MAY MAKE A RUN FOR THE FREEZING MARK
ACROSS INLAND AREAS LATE TONIGHT WHICH OPENS THE POSSIBILITY FOR
BLACK ICE CONCERNS AS ANY LINGERING PUDDLES OR WET SPOTS COULD
FREEZE. WILL CONTINUE TO MENTION THIS POSSIBILITY IN THE HAZARDOUS
WEATHER OUTLOOK.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
A SECONDARY COLD FRONT WILL DROP TOWARD THE REGION FROM THE
NORTHWEST MONDAY...WHILE DEEP UPPER TROUGHING REMAINS IN CONTROL
EARLY NEXT WEEK. WEATHER PATTERN BECOMES QUITE COMPLEX WITH MODEL
SOLUTIONS DIVERGING ON THE DEVELOPMENT OF LOW PRESSURE ALONG THE
DESCENDING BOUNDARY MONDAY AND TUESDAY...THUS INDICATING VERY
DIFFERENT PRECIPITATION POTENTIAL. GFS AND CANADIAN MODELS PAINT
LIGHT PRECIP OVER THE AREA BRIEFLY MONDAY AFTERNOON...WHILE THE
ECMWF DEVELOPS A STRONGER SURFACE LOW AND A SUBSEQUENTLY WETTER
SOLUTION. A CLOSE LOOK AT MODEL WIND AND RH FIELDS SUGGEST THAT
ACCESS TO DEEP MOISTURE WILL BE BRIEF...AS FLOW REMAINS MOSTLY
OFFSHORE DURING THE DAY. HAVE THEREFORE KEPT POPS BELOW 15 PERCENT
FOR MONDAY OVER LAND AREAS UNTIL CONFIDENCE IMPROVES.
STRONG UPPER LEVEL ENERGY ROUNDS THE BASE OF THE UPPER TROUGH AND
CROSSES THROUGH THE SOUTHEAST STATES BY EARLY TUESDAY...ENABLING
LOW PRESSURE TO DEEPEN TO THE SOUTH AND OFFSHORE. THIS COASTAL LOW
WILL QUICKLY PULL TO THE NORTHEAST FURTHER INTO THE ATLANTIC...AND
HAVE THUS INDICATED RAIN CHANCES OVER THE COASTAL WATERS MONDAY
NIGHT INTO TUESDAY. DESPITE MAINTAINING A DRY FORECAST FOR LAND
AREAS AT THIS POINT...WILL NEED TO CAREFULLY MONITOR MODEL TRENDS
REGARDING PRECIP POTENTIAL...ESPECIALLY CONSIDERING A COLDER AIR
MASS WILL ADVECT INTO THE REGION BEHIND THE SECONDARY FRONT AND
COASTAL LOW. TEMPERATURES ARE EXPECTED TO FALL BELOW FREEZING
MONDAY NIGHT.
TUESDAY WILL BE THE COOLEST DAY OF THE LONG TERM PERIOD WITH HIGH
TEMPERATURES ONLY IN THE 40S. DRY HIGH PRESSURE WILL THEN PUSH INTO
THE REGION FROM THE WEST WEDNESDAY AND THURSDAY...ALLOWING FOR A
GRADUAL WARMING TREND. HIGH TEMPERATURES WILL REBOUND BACK TO
SEASONAL NORMALS IN THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY.
A COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY AND PROGRESS
THROUGH THE FORECAST AREA OVER THE WEEKEND. HAVE INDICATED HIGH
TEMPERATURES SLIGHTLY ABOVE NORMALS FRIDAY...AS THE AREA FALLS
WITHIN SOLID SOUTHERLY FLOW IN THE WARM SECTOR OF THE FRONT. HAVE
ALSO INTRODUCED SLIGHT CHANCE POPS FRIDAY AND SATURDAY ASSOCIATED
WITH THE FRONTAL PASSAGE.
&&
.AVIATION /17Z SUNDAY THROUGH THURSDAY/...
LOW-LEVEL WIND SHEAR CONTINUES INTO EARLY AFTERNOON AT KSAV DUE TO
STRONG LOW-LEVEL WINDS AHEAD OF AN APPROACHING COLD FRONT.
OTHERWISE...EXTENSIVE MID-LEVEL CLOUDINESS WITH VFR CIGS WILL
REMAIN ACROSS THE TERMINALS BEFORE BEGINNING TO STEADILY FALL EARLY
THIS AFTERNOON AS A LARGE SWATH OF RAINFALL APPROACHES FROM THE
W. BOTH CIGS AND VSBYS LOOK TO DROP TO MVFR THRESHOLDS BY MID
AFTERNOON...ROUGHLY AFTER 19Z... WITH POCKETS OF HEAVIER RAINFALL
TEMPORARILY DROPPING CONDITIONS EVEN LOWER. EXPECT TEMPO IFR AT
KCHS BETWEEN 18/21-19/01Z AT KCHS AND 18/22-19/02Z AT KSAV WHEN
THE HEAVIEST RAINFALL IS LIKELY. FURTHER REFINEMENTS IN BOTH
TIMING AND INTENSITY OF THE HEAVIEST RAINS WILL LIKELY BE NEEDED
AS SHORT TERM TRENDS BECOME MORE EVIDENT AND WILL CONTINUE TO
MONITOR. MAY SEE MVFR/IFR CIGS REMAIN MUCH OF THE NIGHT EVEN
AFTER THE FRONTAL PASSAGE...ESPECIALLY AT KCHS... AND SO DECIDED
TO TREND THAT WAY IN THE 18Z/18 TAFS. HOWEVER...WITH RELATIVELY
LOW CONFIDENCE AT THIS POINT...HAVE GONE NO LOWER THAN MVFR CONDS.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL THROUGH
THE PERIOD.
&&
.MARINE...
TODAY...WINDS WILL CONTINUE TO INCREASE OVER THE COASTAL WATERS
TODAY AS THE LOW- LEVEL JET AHEAD OF AN APPROACHING COLD FRONT
CONTINUES TO INTENSIFY. STILL LOOKS LIKE THE BEST OPPORTUNITY FOR
WINDS TO REACH SMALL CRAFT ADVISORY THRESHOLDS WILL BE ACROSS THE
GEORGIA OFFSHORE WATERS AND PORTIONS OF THE CHARLESTON COUNTY
COASTAL WATERS BEYOND 15 NM...WHICH IS WHERE THE WARMEST WATER
TEMPERATURES ARE CURRENTLY FOUND.
TONIGHT...WINDS WILL TURN OFFSHORE TONIGHT BEHIND A COLD FRONT.
POST FRONTAL COLD AIR ADVECTION DOES NOT REALLY RAMP UNTIL MONDAY.
THE SMALL CRAFT ADVISORY FOR THE CHARLESTON COUNTY COASTAL
WATERS WILL END LATE THIS EVE BUT WILL CONTINUE FOR THE GA WATERS
BEYOND 20 NM FROM SHORE.
MONDAY THROUGH THURSDAY...OFFSHORE FLOW WILL REMAIN ELEVATED AS A
COLD AIR MASS PERSISTS AND ENHANCES MIXING OVER THE WATERS THROUGH
EARLY NEXT WEEK. SMALL CRAFT ADVISORY WINDS AND SEAS WILL LIKELY
CONTINUE FOR THE OFFSHORE GEORGIA WATERS THROUGH AT LEAST MONDAY
NIGHT. WINDS IN THE NEARSHORE WATERS COULD REACH UP TO 20 KT
DURING THE SAME PERIOD. A WEAK LOW PRESSURE SYSTEM WILL DEVELOP
JUST EAST OF THE MARINE ZONES TUESDAY...THEN QUICKLY PULL
NORTHEAST. A RELATIVELY TIGHT PRESSURE GRADIENT BETWEEN THE
ATLANTIC LOW AND BUILDING HIGH PRESSURE FROM THE WEST WILL
MAINTAIN MODERATE OFFSHORE FLOW INTO MIDWEEK.
THE PRESSURE GRADIENT WILL WEAKEN WHILE HIGH PRESSURE CONTINUES
TO TRACK EAST...ALLOWING WINDS TO GRADUALLY DIMINISH WEDNESDAY AND
THURSDAY.
WINDS WILL BECOME SOUTHWEST AHEAD OF A COLD FRONT APPROACHING FROM
THE WEST AND WILL INCREASE AGAIN LATE FRIDAY INTO THE WEEKEND.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EST
TUESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 10 PM EST
THIS EVENING FOR AMZ350.
&&
$$
000
FXUS62 KCHS 181546
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1046 AM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AND MOVE OFFSHORE
TONIGHT WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH
THURSDAY WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A SHORTWAVE TROUGH DIGGING ACROSS NORTHERN ALABAMA THIS MORNING
WILL LIFT E ACROSS GA/SC TODAY PUSHING A SURFACE COLD FRONT TOWARD
THE AREA AND OFF THE COAST EARLY THIS EVENING. WILL KEEP POPS IN
THE CATEGORICAL RANGE /80S- 90S/ WITH THE HIGHEST POPS ACROSS SRN
SC AS DECENT MOISTURE/LIFT ARE PROGGED TO BE OVER THE AREA. EXPECT
STORM TOTAL RAINFALL AMOUNTS OF 1/2 TO 3/4 OF AN INCH WITH LOCALLY
HIGHER AMOUNTS POSSIBLE.
PINNING DOWN HIGH TEMPERATURES TODAY WILL BE DIFFICULT AT BEST AS
MUCH DEPENDS ON THE CLOUD COVER...WHICH IS ERODING QUICKLY FROM
THE S THIS MORNING...AND THE COVERAGE/INTENSITY OF THE RAIN. THINK
NW AREAS FROM AROUND JAMESTOWN TO RIDGEVILLE TO ALLENDALE TO
SCREVEN WILL LIKELY REMAIN IN THE MID/UPPER 40S TODAY AS THOSE
AREAS ARE ALREADY SEEING RAIN. TEMPS SHOULD REACH AROUND 60
DEGREES DOWN NEAR DARIEN AS MORE BREAKS IN THE CLOUDS AND A LATER
START TO THE RAIN ARE EXPECTED THERE.
OVERALL NOT MUCH CHANGE NEEDED TO THE CURRENT FORECAST.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
SHOWERS WILL QUICKLY END FROM WEST TO EAST TONIGHT AS A COLD FRONT
MOVES OFFSHORE. TEMPERATURES MAY MAKE A RUN FOR THE FREEZING MARK
ACROSS INLAND AREAS LATE TONIGHT WHICH OPENS THE POSSIBILITY FOR
BLACK ICE CONCERNS AS ANY LINGERING PUDDLES OR WET SPOTS COULD
FREEZE. WILL CONTINUE TO MENTION THIS POSSIBILITY IN THE HAZARDOUS
WEATHER OUTLOOK.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
A SECONDARY COLD FRONT WILL DROP TOWARD THE REGION FROM THE
NORTHWEST MONDAY...WHILE DEEP UPPER TROUGHING REMAINS IN CONTROL
EARLY NEXT WEEK. WEATHER PATTERN BECOMES QUITE COMPLEX WITH MODEL
SOLUTIONS DIVERGING ON THE DEVELOPMENT OF LOW PRESSURE ALONG THE
DESCENDING BOUNDARY MONDAY AND TUESDAY...THUS INDICATING VERY
DIFFERENT PRECIPITATION POTENTIAL. GFS AND CANADIAN MODELS PAINT
LIGHT PRECIP OVER THE AREA BRIEFLY MONDAY AFTERNOON...WHILE THE
ECMWF DEVELOPS A STRONGER SURFACE LOW AND A SUBSEQUENTLY WETTER
SOLUTION. A CLOSE LOOK AT MODEL WIND AND RH FIELDS SUGGEST THAT
ACCESS TO DEEP MOISTURE WILL BE BRIEF...AS FLOW REMAINS MOSTLY
OFFSHORE DURING THE DAY. HAVE THEREFORE KEPT POPS BELOW 15 PERCENT
FOR MONDAY OVER LAND AREAS UNTIL CONFIDENCE IMPROVES.
STRONG UPPER LEVEL ENERGY ROUNDS THE BASE OF THE UPPER TROUGH AND
CROSSES THROUGH THE SOUTHEAST STATES BY EARLY TUESDAY...ENABLING
LOW PRESSURE TO DEEPEN TO THE SOUTH AND OFFSHORE. THIS COASTAL LOW
WILL QUICKLY PULL TO THE NORTHEAST FURTHER INTO THE ATLANTIC...AND
HAVE THUS INDICATED RAIN CHANCES OVER THE COASTAL WATERS MONDAY
NIGHT INTO TUESDAY. DESPITE MAINTAINING A DRY FORECAST FOR LAND
AREAS AT THIS POINT...WILL NEED TO CAREFULLY MONITOR MODEL TRENDS
REGARDING PRECIP POTENTIAL...ESPECIALLY CONSIDERING A COLDER AIR
MASS WILL ADVECT INTO THE REGION BEHIND THE SECONDARY FRONT AND
COASTAL LOW. TEMPERATURES ARE EXPECTED TO FALL BELOW FREEZING
MONDAY NIGHT.
TUESDAY WILL BE THE COOLEST DAY OF THE LONG TERM PERIOD WITH HIGH
TEMPERATURES ONLY IN THE 40S. DRY HIGH PRESSURE WILL THEN PUSH INTO
THE REGION FROM THE WEST WEDNESDAY AND THURSDAY...ALLOWING FOR A
GRADUAL WARMING TREND. HIGH TEMPERATURES WILL REBOUND BACK TO
SEASONAL NORMALS IN THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY.
A COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY AND PROGRESS
THROUGH THE FORECAST AREA OVER THE WEEKEND. HAVE INDICATED HIGH
TEMPERATURES SLIGHTLY ABOVE NORMALS FRIDAY...AS THE AREA FALLS
WITHIN SOLID SOUTHERLY FLOW IN THE WARM SECTOR OF THE FRONT. HAVE
ALSO INTRODUCED SLIGHT CHANCE POPS FRIDAY AND SATURDAY ASSOCIATED
WITH THE FRONTAL PASSAGE.
&&
.AVIATION /15Z SUNDAY THROUGH THURSDAY/...
LOW- LEVEL WIND SHEAR CONTINUES INTO EARLY AFTERNOON DUE TO STRONG
LOW-LEVEL WINDS AHEAD OF AN APPROACHING COLD FRONT.
OTHERWISE...EXTENSIVE MID-LEVEL CLOUDINESS WITH VFR CEILINGS WILL
REMAIN ACROSS THE TERMINALS BEFORE CEILINGS BEGIN TO STEADILY
FALL BY EARLY AFTERNOON AS A LARGE SWATH OF RAINFALL APPROACHES
FROM THE WEST. BOTH CEILINGS AND VISIBILITIES LOOK TO DROP TO MVFR
THRESHOLDS BY MID AFTERNOON...ROUGHLY AFTER 19Z... WITH POCKETS OF
HEAVIER RAINFALL TEMPORARILY DROPPING CONDITIONS EVEN LOWER.
EXPECT TEMPO IFR AT KCHS BETWEEN 18/21-19/01Z AT KCHS AND
18/22-19/02Z AT KSAV. FURTHER REFINEMENTS IN BOTH TIMING AND
INTENSITY OF THE HEAVIEST RAINS WILL LIKELY BE NEEDED AS SHORT
TERM TRENDS BECOME MORE EVIDENT. VFR CONDITIONS ARE LIKELY TO
RETURN BY LATE IN THE PERIOD WITH CLEARING SKIES AT BOTH
TERMINALS.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL THROUGH
THE PERIOD.
&&
.MARINE...
TODAY...WINDS WILL CONTINUE TO INCREASE OVER THE COASTAL WATERS
TODAY AS THE LOW- LEVEL JET AHEAD OF AN APPROACHING COLD FRONT
CONTINUES TO INTENSIFY. STILL LOOKS LIKE THE BEST OPPORTUNITY FOR
WINDS TO REACH SMALL CRAFT ADVISORY THRESHOLDS WILL BE ACROSS THE
GEORGIA OFFSHORE WATERS AND PORTIONS OF THE CHARLESTON COUNTY
COASTAL WATERS BEYOND 15 NM...WHICH IS WHERE THE WARMEST WATER
TEMPERATURES ARE CURRENTLY FOUND.
TONIGHT...WINDS WILL TURN OFFSHORE TONIGHT BEHIND A COLD FRONT.
POST FRONTAL COLD AIR ADVECTION DOES NOT REALLY RAMP UNTIL MONDAY.
THE SMALL CRAFT ADVISORY FOR THE CHARLESTON COUNTY COASTAL
WATERS WILL END LATE THIS EVE BUT WILL CONTINUE FOR THE GA WATERS
BEYOND 20 NM FROM SHORE.
MONDAY THROUGH THURSDAY...OFFSHORE FLOW WILL REMAIN ELEVATED AS A
COLD AIR MASS PERSISTS AND ENHANCES MIXING OVER THE WATERS THROUGH
EARLY NEXT WEEK. SMALL CRAFT ADVISORY WINDS AND SEAS WILL LIKELY
CONTINUE FOR THE OFFSHORE GEORGIA WATERS THROUGH AT LEAST MONDAY
NIGHT. WINDS IN THE NEARSHORE WATERS COULD REACH UP TO 20 KT
DURING THE SAME PERIOD. A WEAK LOW PRESSURE SYSTEM WILL DEVELOP
JUST EAST OF THE MARINE ZONES TUESDAY...THEN QUICKLY PULL
NORTHEAST. A RELATIVELY TIGHT PRESSURE GRADIENT BETWEEN THE
ATLANTIC LOW AND BUILDING HIGH PRESSURE FROM THE WEST WILL
MAINTAIN MODERATE OFFSHORE FLOW INTO MIDWEEK.
THE PRESSURE GRADIENT WILL WEAKEN WHILE HIGH PRESSURE CONTINUES
TO TRACK EAST...ALLOWING WINDS TO GRADUALLY DIMINISH WEDNESDAY AND
THURSDAY.
WINDS WILL BECOME SOUTHWEST AHEAD OF A COLD FRONT APPROACHING FROM
THE WEST AND WILL INCREASE AGAIN LATE FRIDAY INTO THE WEEKEND.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EST
TUESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 10 PM EST
THIS EVENING FOR AMZ350.
&&
$$
RJB
000
FXUS62 KCHS 181132
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
632 AM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AND MOVE OFFSHORE
TONIGHT WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH
THURSDAY WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
A FEW CHANGES ARE NEEDED TO THE FORECAST. FIRST...RUC SOUNDINGS
SUGGEST THE RISK FOR SLEET HAS JUST ABOUT ENDED ACROSS INLAND
LOCALES. HAVE SEEN A FEW ENHANCED RETURNS IN THE PRECIPITATION
MOVING FROM JENKINS-ALLENDALE BUT SO FAR NO REPORTS OF SLEET HAVE
BEEN RECEIVED. WILL REMOVE ALL MENTION OF SLEET WITH AN UPDATE
SHORTLY. SECOND...RADAR TRENDS ACROSS SOUTHERN ALABAMA AND WESTERN
GEORGIA SUGGEST Q-C FORCING IS STARTING TO RAPIDLY INCREASE AHEAD
OF THE SHARPENING SHORTWAVE DIVING ACROSS NORTHERN ARKANSAS.
18/06Z SREF POP PROGS CONTINUE TO HIGHLIGHT NEAR 100 PERCENT POPS
TODAY FOR MUCH OF THE AREA SO WILL INCREASE POPS SLIGHTLY TO 80-90
PERCENT WITH THE HIGHEST POPS AND QPF CENTERED ACROSS OUR SOUTH
CAROLINA ZONES. THE DAY SHIFT MAY VERY WELL HAVE TO COMMIT TO 100
PERCENT POPS LATER THIS MORNING.
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AS A POTENT
SHORTWAVE DROPS SOUTH OUT OF THE MID-MISSISSIPPI VALLEY. SCATTERED
SHOWER ACTIVITY FORMING ACROSS THE DEEP SOUTH THIS MORNING WILL
STEADILY PROGRESS EAST AND INCREASE IN BOTH COVERAGE AND INTENSITY
THIS AFTERNOON AS THE AFOREMENTIONED SHORTWAVE ROUNDS THE BASE OF
THE LONG-WAVE TROUGH AND BECOMES NEGATIVELY TILTED ACROSS SOUTH
CAROLINA/GEORGIA. BOTH THE NAM AND GFS WITH SUPPORT FROM THE
LATEST SHORT RANGE ENSEMBLE MEAN ARE CONSISTENT IN BRING THE CORE
OF THE STRONGEST QUASI-GEOSTROPHIC FORCING ACROSS THE AREA THIS
AFTERNOON...ROUGHLY IN THE 18-00Z TIME FRAME. WILL SHOW POPS
INCREASING FROM WEST TO EAST THIS MORNING WITH 80-90 PERCENT POPS
PREVAILING THIS AFTERNOON INTO VERY EARLY THIS EVENING. EXPECT
STORM TOTAL RAINFALL AMOUNTS OF 1/2 TO 3/4 INCH WITH LOCALLY
HIGHER AMOUNTS.
PINNING DOWN HIGH TEMPERATURES TODAY IS PROVING TO BE EXTREMELY
DIFFICULT. ALTHOUGH WET-BULB TEMPERATURES WILL INCREASE INTO THE
UPPER 30S TO LOWER 40S THIS AFTERNOON THERE WILL LIKELY BE ENOUGH
EVAPORATIONAL COOLING AT THE ONSET OF THE RAIN TO KEEP THE AREA
NORTH OF A MILLEN-HAMPTON-JAMESTOWN LINE IN THE MID-UPPER 40S.
FARTHER SOUTH AND EAST THE RAIN WILL BE SLOWER GETTING INTO THESE
AREAS SO HIGHS SHOULD BE ABLE TO REACH THE LOWER-MID 50S EXCEPT
ACROSS THE FAR SOUTH WHERE UPPER 50S TO AROUND 60 APPEAR MORE
PROBABLE. FURTHER REFINEMENTS APPEAR LIKELY LATER THIS MORNING AS
SHORT TERM PRECIPITATION AND TEMPERATURE TRENDS BECOME MORE
APPARENT.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
SHOWERS WILL QUICKLY END FROM WEST TO EAST TONIGHT AS A COLD FRONT
MOVES OFFSHORE. TEMPERATURES MAY MAKE A RUN FOR THE FREEZING MARK
ACROSS INLAND AREAS LATE TONIGHT WHICH OPENS THE POSSIBILITY FOR
BLACK ICE CONCERNS AS ANY LINGERING PUDDLES OR WET SPOTS COULD
FREEZE. WILL CONTINUE TO MENTION THIS POSSIBILITY IN THE HAZARDOUS
WEATHER OUTLOOK.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
A SECONDARY COLD FRONT WILL DROP TOWARD THE REGION FROM THE
NORTHWEST MONDAY...WHILE DEEP UPPER TROUGHING REMAINS IN CONTROL
EARLY NEXT WEEK. WEATHER PATTERN BECOMES QUITE COMPLEX WITH MODEL
SOLUTIONS DIVERGING ON THE DEVELOPMENT OF LOW PRESSURE ALONG THE
DESCENDING BOUNDARY MONDAY AND TUESDAY...THUS INDICATING VERY
DIFFERENT PRECIPITATION POTENTIAL. GFS AND CANADIAN MODELS PAINT
LIGHT PRECIP OVER THE AREA BRIEFLY MONDAY AFTERNOON...WHILE THE
ECMWF DEVELOPS A STRONGER SURFACE LOW AND A SUBSEQUENTLY WETTER
SOLUTION. A CLOSE LOOK AT MODEL WIND AND RH FIELDS SUGGEST THAT
ACCESS TO DEEP MOISTURE WILL BE BRIEF...AS FLOW REMAINS MOSTLY
OFFSHORE DURING THE DAY. HAVE THEREFORE KEPT POPS BELOW 15 PERCENT
FOR MONDAY OVER LAND AREAS UNTIL CONFIDENCE IMPROVES.
STRONG UPPER LEVEL ENERGY ROUNDS THE BASE OF THE UPPER TROUGH AND
CROSSES THROUGH THE SOUTHEAST STATES BY EARLY TUESDAY...ENABLING
LOW PRESSURE TO DEEPEN TO THE SOUTH AND OFFSHORE. THIS COASTAL LOW
WILL QUICKLY PULL TO THE NORTHEAST FURTHER INTO THE ATLANTIC...AND
HAVE THUS INDICATED RAIN CHANCES OVER THE COASTAL WATERS MONDAY
NIGHT INTO TUESDAY. DESPITE MAINTAINING A DRY FORECAST FOR LAND
AREAS AT THIS POINT...WILL NEED TO CAREFULLY MONITOR MODEL TRENDS
REGARDING PRECIP POTENTIAL...ESPECIALLY CONSIDERING A COLDER AIR
MASS WILL ADVECT INTO THE REGION BEHIND THE SECONDARY FRONT AND
COASTAL LOW. TEMPERATURES ARE EXPECTED TO FALL BELOW FREEZING
MONDAY NIGHT.
TUESDAY WILL BE THE COOLEST DAY OF THE LONG TERM PERIOD WITH HIGH
TEMPERATURES ONLY IN THE 40S. DRY HIGH PRESSURE WILL THEN PUSH INTO
THE REGION FROM THE WEST WEDNESDAY AND THURSDAY...ALLOWING FOR A
GRADUAL WARMING TREND. HIGH TEMPERATURES WILL REBOUND BACK TO
SEASONAL NORMALS IN THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY.
A COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY AND PROGRESS
THROUGH THE FORECAST AREA OVER THE WEEKEND. HAVE INDICATED HIGH
TEMPERATURES SLIGHTLY ABOVE NORMALS FRIDAY...AS THE AREA FALLS
WITHIN SOLID SOUTHERLY FLOW IN THE WARM SECTOR OF THE FRONT. HAVE
ALSO INTRODUCED SLIGHT CHANCE POPS FRIDAY AND SATURDAY ASSOCIATED
WITH THE FRONTAL PASSAGE.
&&
.AVIATION /11Z SUNDAY THROUGH THURSDAY/...
PREVIOUS TAF SET LOOKS GOOD. OPTED TO EXTEND A MENTION OF LOW-LEVEL
WIND SHEAR /LLWS/ UNTIL LATE MORNING AS MODEL PROGS NOW HAVE
1000-2000 FT WINDS INCREASING TO 40 KT DURING THIS TIME.
EXTENSIVE MID-LEVEL CLOUDINESS WITH VFR CEILINGS WILL REMAIN
ACROSS THE TERMINALS FOR THE NEXT 6 HOURS BEFORE CEILINGS BEGIN TO
STEADILY FALL BY EARLY AFTERNOON AS A LARGE SWATH OF RAINFALL
APPROACHES FROM THE WEST. BOTH CEILINGS AND VISIBILITIES LOOK TO
DROP TO MVFR THRESHOLDS BY MID AFTERNOON...ROUGHLY AFTER 19Z...
WITH POCKETS OF HEAVIER RAINFALL TEMPORARILY DROPPING CONDITIONS
EVEN LOWER. EXPECT TEMPO IFR AT KCHS BETWEEN 18/21-19/01Z AT KCHS
AND 18/22-19/02Z AT KSAV. FURTHER REFINEMENTS IN BOTH TIMING AND
INTENSITY OF THE HEAVIEST RAINS WILL LIKELY BE NEEDED LATER THIS
MORNING AS SHORT TERM TRENDS BECOME MORE EVIDENT. VFR CONDITIONS
ARE LIKELY TO RETURN BY LATE IN THE PERIOD WITH CLEARING SKIES AT
BOTH TERMINALS.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL THROUGH
THE PERIOD.
&&
.MARINE...
WINDS ARE STARTING TO INCREASE ACROSS THE COASTAL WATERS THIS
MORNING AS THE LOW-LEVEL JET CONTINUES TO INTENSIFY. STILL LOOKS
LIKE THE BEST OPPORTUNITY FOR WINDS TO REACH SMALL CRAFT ADVISORY
THRESHOLDS WILL BE ACROSS THE GEORGIA OFFSHORE WATERS AND PORTIONS
OF THE CHARLESTON COUNTY COASTAL WATERS BEYOND 15 NM...WHICH IS
WHERE THE WARMEST WATER TEMPERATURES ARE CURRENTLY FOUND. WINDS
WILL TURN OFFSHORE TONIGHT BEHIND A COLD FRONT. POST FRONTAL COLD
AIR ADVECTION DOES NOT REALLY RAMP UNTIL MONDAY. WILL MAKE MINOR
MODIFICATIONS TO THE GOING SMALL CRAFT ADVISORY...MAINLY TO
SHORTEN ITS ENDING TIME ACROSS THE CHARLESTON COUNTY COASTAL
WATERS.
MONDAY THROUGH THURSDAY...OFFSHORE FLOW WILL REMAIN ELEVATED AS A
COLD AIR MASS PERSISTS AND ENHANCES MIXING OVER THE WATERS THROUGH
EARLY NEXT WEEK. SMALL CRAFT ADVISORY WINDS AND SEAS WILL LIKELY
CONTINUE FOR THE OFFSHORE GEORGIA WATERS THROUGH AT LEAST MONDAY
NIGHT. WINDS IN THE NEARSHORE WATERS COULD REACH UP TO 20 KT
DURING THE SAME PERIOD. A WEAK LOW PRESSURE SYSTEM WILL DEVELOP
JUST EAST OF THE MARINE ZONES TUESDAY...THEN QUICKLY PULL
NORTHEAST. A RELATIVELY TIGHT PRESSURE GRADIENT BETWEEN THE
ATLANTIC LOW AND BUILDING HIGH PRESSURE FROM THE WEST WILL
MAINTAIN MODERATE OFFSHORE FLOW INTO MIDWEEK.
THE PRESSURE GRADIENT WILL WEAKEN WHILE HIGH PRESSURE CONTINUES
TO TRACK EAST...ALLOWING WINDS TO GRADUALLY DIMINISH WEDNESDAY AND
THURSDAY.
WINDS WILL BECOME SOUTHWEST AHEAD OF A COLD FRONT APPROACHING FROM
THE WEST AND WILL INCREASE AGAIN LATE FRIDAY INTO THE WEEKEND.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EST
TUESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 10 PM EST
THIS EVENING FOR AMZ350.
&&
$$
ST
000
FXUS62 KCHS 180834
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
334 AM EST SUN JAN 18 2009
.SYNOPSIS...
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AND MOVE OFFSHORE
TONIGHT WITH A SECONDARY COLD FRONT TO PUSH THROUGH LATE MONDAY
INTO TUESDAY. HIGH PRES WILL THEN BUILD INTO THE AREA THROUGH
THURSDAY WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /THROUGH TODAY/...
MODEST WARM AIR ADVECTION HAS SETTLE IN ACROSS THE REGION THIS
MORNING IN ASSOCIATION WITH A 30-40 KT LOW-LEVEL JET. ATTENDANT
ISENTROPIC LIFT IS SUPPORTING PATCHES OF VERY LIGHT PRECIPITATION
ACROSS THE FORECAST AREA. WE HAVE RECEIVED A FEW SKYWARN SPOTTER
REPORTS OF SLEET UP AND DOWN THE COAST WHERE 06Z BUFR SOUNDINGS
WERE SUPPORTIVE OF SLEET FORMATION BUT THERE HAVE BEEN NO REPORTS
OF ACCUMULATION NOW THAT SURFACE TEMPERATURES ABOVE FREEZING.
WHILE SPOTTY PRECIPITATION WILL CONTINUE FOR THE NEXT SEVERAL
HOURS...MODEL SOUNDINGS SUGGEST THE DEPTH OF THE 900MB WARM NOSE
WILL INCREASE SUFFICIENTLY ENOUGH TO CHANGE ANY FROZEN
PRECIPITATION OVER THE VERY LIGHT RAIN BY SUNRISE OR SHORTLY
THEREAFTER. UPSTREAM RADAR TRENDS SUGGEST A SLIGHT CHANCE FOR
SHOWERS AND SLEET WILL BE NEEDED ACROSS THE FAR INTERIOR FOR THE
NEXT FEW HOURS...BUT AGAIN NO ACCUMULATIONS ARE EXPECTED.
A COLD FRONT WILL APPROACH FROM THE WEST TODAY AS A POTENT
SHORTWAVE DROPS SOUTH OUT OF THE MID-MISSISSIPPI VALLEY. SCATTERED
SHOWER ACTIVITY FORMING ACROSS THE DEEP SOUTH THIS MORNING WILL
STEADILY PROGRESS EAST AND INCREASE IN BOTH COVERAGE AND INTENSITY
THIS AFTERNOON AS THE AFOREMENTIONED SHORTWAVE ROUNDS THE BASE OF
THE LONG-WAVE TROUGH AND BECOMES NEGATIVELY TILTED ACROSS SOUTH
CAROLINA/GEORGIA. BOTH THE NAM AND GFS WITH SUPPORT FROM THE
LATEST SHORT RANGE ENSEMBLE MEAN ARE CONSISTENT IN BRING THE CORE
OF THE STRONGEST QUASI-GEOSTROPHIC FORCING ACROSS THE AREA THIS
AFTERNOON...ROUGHLY IN THE 18-00Z TIME FRAME. WILL SHOW POPS
INCREASING FROM WEST TO EAST THIS MORNING WITH 70-80 PERCENT POPS
PREVAILING THIS AFTERNOON INTO VERY EARLY THIS EVENING. EXPECT
STORM TOTAL RAINFALL AMOUNTS OF 1/2 TO 3/4 INCH WITH LOCALLY
HIGHER AMOUNTS.
PINNING DOWN HIGH TEMPERATURES TODAY IS PROVING TO BE EXTREMELY
DIFFICULT. ALTHOUGH WET-BULB TEMPERATURES WILL INCREASE INTO THE
UPPER 30S TO LOWER 40S THIS AFTERNOON THERE WILL LIKELY BE ENOUGH
EVAPORATIONAL COOLING AT THE ONSET OF THE RAIN TO KEEP THE AREA
NORTH OF A MILLEN- HAMPTON-JAMESTOWN LINE IN THE MID-UPPER 40S.
FARTHER SOUTH AND EAST THE RAIN WILL BE SLOWER GETTING INTO THESE
AREAS SO HIGHS SHOULD BE ABLE TO REACH THE LOWER-MID 50S EXCEPT
ACROSS THE FAR SOUTH WHERE UPPER 50S TO AROUND 60 APPEAR MORE
PROBABLE. FURTHER REFINEMENTS APPEAR LIKELY LATER THIS MORNING AS
SHORT TERM PRECIPITATION AND TEMPERATURE TRENDS BECOME MORE
APPARENT.
&&
.SHORT TERM /TONIGHT/...
SHOWERS WILL QUICKLY END FROM WEST TO EAST TONIGHT AS A COLD FRONT
MOVES OFFSHORE. TEMPERATURES MAY MAKE A RUN FOR THE FREEZING MARK
ACROSS INLAND AREAS LATE TONIGHT WHICH OPENS THE POSSIBILITY FOR
BLACK ICE CONCERNS AS ANY LINGERING PUDDLES OR WET SPOTS COULD
FREEZE. WILL CONTINUE TO MENTION THIS POSSIBILITY IN THE HAZARDOUS
WEATHER OUTLOOK.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
A SECONDARY COLD FRONT WILL DROP TOWARD THE REGION FROM THE
NORTHWEST MONDAY...WHILE DEEP UPPER TROUGHING REMAINS IN CONTROL
EARLY NEXT WEEK. WEATHER PATTERN BECOMES QUITE COMPLEX WITH MODEL
SOLUTIONS DIVERGING ON THE DEVELOPMENT OF LOW PRESSURE ALONG THE
DESCENDING BOUNDARY MONDAY AND TUESDAY...THUS INDICATING VERY
DIFFERENT PRECIPITATION POTENTIAL. GFS AND CANADIAN MODELS PAINT
LIGHT PRECIP OVER THE AREA BRIEFLY MONDAY AFTERNOON...WHILE THE
ECMWF DEVELOPS A STRONGER SURFACE LOW AND A SUBSEQUENTLY WETTER
SOLUTION. A CLOSE LOOK AT MODEL WIND AND RH FIELDS SUGGEST THAT
ACCESS TO DEEP MOISTURE WILL BE BRIEF...AS FLOW REMAINS MOSTLY
OFFSHORE DURING THE DAY. HAVE THEREFORE KEPT POPS BELOW 15 PERCENT
FOR MONDAY OVER LAND AREAS UNTIL CONFIDENCE IMPROVES.
STRONG UPPER LEVEL ENERGY ROUNDS THE BASE OF THE UPPER TROUGH AND
CROSSES THROUGH THE SOUTHEAST STATES BY EARLY TUESDAY...ENABLING
LOW PRESSURE TO DEEPEN TO THE SOUTH AND OFFSHORE. THIS COASTAL LOW
WILL QUICKLY PULL TO THE NORTHEAST FURTHER INTO THE ATLANTIC...AND
HAVE THUS INDICATED RAIN CHANCES OVER THE COASTAL WATERS MONDAY
NIGHT INTO TUESDAY. DESPITE MAINTAINING A DRY FORECAST FOR LAND
AREAS AT THIS POINT...WILL NEED TO CAREFULLY MONITOR MODEL TRENDS
REGARDING PRECIP POTENTIAL...ESPECIALLY CONSIDERING A COLDER AIR
MASS WILL ADVECT INTO THE REGION BEHIND THE SECONDARY FRONT AND
COASTAL LOW. TEMPERATURES ARE EXPECTED TO FALL BELOW FREEZING
MONDAY NIGHT.
TUESDAY WILL BE THE COOLEST DAY OF THE LONG TERM PERIOD WITH HIGH
TEMPERATURES ONLY IN THE 40S. DRY HIGH PRESSURE WILL THEN PUSH INTO
THE REGION FROM THE WEST WEDNESDAY AND THURSDAY...ALLOWING FOR A
GRADUAL WARMING TREND. HIGH TEMPERATURES WILL REBOUND BACK TO
SEASONAL NORMALS IN THE UPPER 50S TO AROUND 60 DEGREES ON THURSDAY.
A COLD FRONT WILL APPROACH FROM THE WEST ON FRIDAY AND PROGRESS
THROUGH THE FORECAST AREA OVER THE WEEKEND. HAVE INDICATED HIGH
TEMPERATURES SLIGHTLY ABOVE NORMALS FRIDAY...AS THE AREA FALLS
WITHIN SOLID SOUTHERLY FLOW IN THE WARM SECTOR OF THE FRONT. HAVE
ALSO INTRODUCED SLIGHT CHANCE POPS FRIDAY AND SATURDAY ASSOCIATED
WITH THE FRONTAL PASSAGE.
&&
.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
THERE REMAINS A RISK FOR LOW-LEVEL WIND SHEAR /LLWS/ AT THE KSAV
TERMINAL TONIGHT AS SURFACE WINDS REMAIN LIGHT AND 1500 FT WINDS
INCREASE TO AS HIGH AS 30-35 KT AFTER 09Z. 00Z MODEL GUIDANCE HAS
TRENDED SLIGHTLY HIGHER WITH 1500 FT WINDS AT KCHS SO A MENTION OF
LLWS WILL BE EXPANDED TO INCLUDE THE TERMINAL WITH THE 06Z TAF
CYCLE. THE RISK FOR LLWS WILL DIMINISH BY 14Z ONCE THE NOCTURNAL
INVERSION BREAKS AND SURFACE WINDS BEGIN TO INCREASE.
EXTENSIVE MID-LEVEL CLOUDINESS WITH VFR CEILINGS WILL REMAIN
ACROSS THE TERMINALS FOR THE NEXT 12 HOURS BEFORE CEILINGS BEGIN
TO STEADILY FALL BY EARLY AFTERNOON AS A LARGE SWATH OF RAINFALL
APPROACHES FROM THE WEST. BOTH CEILINGS AND VISIBILITIES LOOK TO
DROP TO MVFR THRESHOLDS BY MID AFTERNOON...ROUGHLY AFTER 19Z...
WITH POCKETS OF HEAVIER RAINFALL TEMPORARILY DROPPING CONDITIONS
EVEN LOWER. EXPECT TEMPO IFR AT KCHS BETWEEN 18/21-19/00Z AT KCHS
AND 18/21-19/01Z AT KSAV. FURTHER REFINEMENTS IN BOTH TIMING AND
INTENSITY OF THE HEAVIEST RAINS WILL LIKELY BE NEEDED LATER THIS
MORNING AS SHORT TERM TRENDS BECOME MORE EVIDENT. VFR CONDITIONS
ARE LIKELY TO RETURN BY LATE IN THE PERIOD WITH CLEARING SKIES AT
BOTH TERMINALS.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL THROUGH
THE PERIOD.
&&
.MARINE...
WINDS ARE STARTING TO INCREASE ACROSS THE COASTAL WATERS THIS
MORNING AS THE LOW-LEVEL JET CONTINUES TO INTENSIFY. STILL LOOKS
LIKE THE BEST OPPORTUNITY FOR WINDS TO REACH SMALL CRAFT ADVISORY
THRESHOLDS WILL BE ACROSS THE GEORGIA OFFSHORE WATERS AND PORTIONS
OF THE CHARLESTON COUNTY COASTAL WATERS BEYOND 15 NM...WHICH IS
WHERE THE WARMEST WATER TEMPERATURES ARE CURRENTLY FOUND. WINDS
WILL TURN OFFSHORE TONIGHT BEHIND A COLD FRONT. POST FRONTAL COLD
AIR ADVECTION DOES NOT REALLY RAMP UNTIL MONDAY. WILL MAKE MINOR
MODIFICATIONS TO THE GOING SMALL CRAFT ADVISORY...MAINLY TO
SHORTEN ITS ENDING TIME ACROSS THE CHARLESTON COUNTY COASTAL
WATERS.
MONDAY THROUGH THURSDAY...OFFSHORE FLOW WILL REMAIN ELEVATED AS A
COLD AIR MASS PERSISTS AND ENHANCES MIXING OVER THE WATERS THROUGH
EARLY NEXT WEEK. SMALL CRAFT ADVISORY WINDS AND SEAS WILL LIKELY
CONTINUE FOR THE OFFSHORE GEORGIA WATERS THROUGH AT LEAST MONDAY
NIGHT. WINDS IN THE NEARSHORE WATERS COULD REACH UP TO 20 KT
DURING THE SAME PERIOD. A WEAK LOW PRESSURE SYSTEM WILL DEVELOP
JUST EAST OF THE MARINE ZONES TUESDAY...THEN QUICKLY PULL
NORTHEAST. A RELATIVELY TIGHT PRESSURE GRADIENT BETWEEN THE
ATLANTIC LOW AND BUILDING HIGH PRESSURE FROM THE WEST WILL
MAINTAIN MODERATE OFFSHORE FLOW INTO MIDWEEK.
THE PRESSURE GRADIENT WILL WEAKEN WHILE HIGH PRESSURE CONTINUES
TO TRACK EAST...ALLOWING WINDS TO GRADUALLY DIMINISH WEDNESDAY AND
THURSDAY.
WINDS WILL BECOME SOUTHWEST AHEAD OF A COLD FRONT APPROACHING FROM
THE WEST AND WILL INCREASE AGAIN LATE FRIDAY INTO THE WEEKEND.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EST
TUESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 10 PM EST
THIS EVENING FOR AMZ350.
&&
$$
ST/79
000
FXUS62 KCHS 180533
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1233 AM EST SUN JAN 18 2009
.SYNOPSIS...
HIGH PRES ACROSS THE AREA THIS EVENING WILL SHIFT SOUTH OF THE
AREA TONIGHT AND SUNDAY. A COLD FRONT WILL MOVE THROUGH LATE
SUNDAY OR SUNDAY NIGHT...WITH A SECONDARY COLD FRONT TO PUSH
THROUGH ON MONDAY. HIGH PRES WILL BUILD INTO THE AREA THROUGH
THURSDAY...WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
00Z CHARLESTON SOUNDING STILL QUITE DRY WITH VERY LOW DEW POINTS
BELOW 850 MB. WARMER AIR SHOWING UP AT 850 MB THIS EVENING WITH
TEMPS NOW GREATER THAN ZERO C.
CLOUDINESS MOVING IN FROM THE W WAS THINNING A BIT AND STARTING
OFF AT ALTOCUMULUS IN THE 9-10 KFT RANGE. VERY FAST SURFACE TEMP
FALLS NOTED AFTER SUNSET THIS EVENING AND OUR FORECAST READINGS
SEEM ON TRACK BY SHOWING COLDER TEMPS THIS EVENING WITH A TREND
FOR SLOW RISES OVERNIGHT WITH THE CLOUDS AND INTENSIFYING WARM
AIR ADVECTION PATTERN OFF THE STABLE SURFACE INVERSION.
REGIONAL RADAR MOSAIC SHOWS SOME LIGHT RADAR RETURNS OVER PARTS OF
N AND W GEORGIA THIS EVENING WHERE SURFACE TEMPERATURES WERE IN
THE UPPER 30S TO LOWER 40S. APPARENTLY LITTLE IF ANY OF THIS WAS
REACHING THE GROUND...HOWEVER A FEW SNOW FLAKES WERE RECENTLY
REPORTED ALONG I-20 TO THE W OF COLUMBIA. A STRONGER SHORT WAVE ON
TAP LATER TONIGHT...PRECIP MAINLY IN THE FORM OF RAIN SHOULD BREAK
OUT TO OUR W LATE. OF COURSE...IF ANYTHING LIGHT REACHES THE GROUND
OVER OUR ZONES LATE IT COULD FREEZE ON CONTACT BUT AT THIS TIME AS
WAS THE CASE TODAY...IT SEEMS DOUBTFUL WITH ALL THE VERY DRY AIR
ALOFT INITIALLY IN PLACE THAT WE WILL SEEM ANY SIGNIFICANT PRECIP
TONIGHT.
&&
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TODAY/...
REINFORCING SHORT WAVE INTO THE EASTERN LONG WAVE TROUGH MOVES
INTO THE AREA SUNDAY AFTERNOON AND THROUGH THE AREA SUNDAY
EVENING. ASSOCIATED WITH THIS FEATURE ALOFT IS A SURFACE COLD
FRONT...THAT MOVES INTO THE AREA FROM THE WEST AND NW LATE
SUNDAY...AND THROUGH THE ATLC WATERS EARLY SUNDAY NIGHT.
THERE ARE DEFINITELY DECENT WIND FIELDS ACROSS THE AREA SUNDAY
AFTERNOON AND EVENING...WITH AN UPPER LEVEL JET MAX OF 100-100
KT...LOW LEVEL JET OF 30-40 KT AND A NOTICEABLE INCREASE IN
MOISTURE AS PWATS CLIMB TO NEAR OR OVER AN INCH OVER MOST
LOCATIONS BY 00Z MONDAY. THE RESULT WILL BE FOR AN INCREASING
CHANCE OF SHOWERS FROM WEST TO EAST DURING THE AFTERNOON AND
EVENING HOURS...BEFORE ACTIVITY SHIFTS EAST OF THE AREA BY
MIDNIGHT SUNDAY NIGHT.
THE BEST LIFT...MOISTURE AND CONVERGENCE AHEAD OF THE FRONT DOES
NOT MOVE INTO THE FORECAST AREA UNTIL LATE MORNING OR EARLY
AFTERNOON. THUS WE WILL SHOW ONLY SMALL POPS ACROSS WESTERN AREAS
DURING THE MORNING...BUT RAMP POPS UP FROM WEST TO EAST DURING THE
MID AND LATE AFTERNOON...WITH LIKELY POPS MOST COMMUNITIES EXCEPT
FAR SE SECTIONS. THESE POPS WILL CONTINUE INTO THE EVENING...THEN
TAPER OFF FROM WEST TO EAST IN WAKE OF THE FRONT SUNDAY NIGHT.
MID LEVEL LAPSE RATES ARE MODEST CONSIDERING THE TIME OF THE
YEAR...CLOSE TO 6 DEGREES CELSIUS...BUT THERE IS LITTLE TO NO CAPE
OR INSTABILITY...SO WE ANTICIPATE JUST SHOWERS. MAYBE A FEW
T-STORMS OVER THE GULF STREAM SUNDAY NIGHT AS THE COLD FRONT
APPROACHES...BUT FOR THE MOST PART JUST SHOWERS.
LOOKING AT ABOUT 4-6 HOURS OF PRECIP SUNDAY AFTERNOON AND
EVENING...AND THAT ALONG WITH POPS OF 60-70 PERCENT AND THE
INCREASED IN PWATS WILL RESULT IN ABOUT 1/4 INCH MOST
LOCATIONS...WITH LOCAL AMOUNTS UP TO 1/2 INCH WITH THIS RAIN
EVENT.
TEMPS WILL CERTAINLY BE OF CONCERN SUNDAY...BUT DEFINITELY WARMER
THAN RECENT DAYS. THE INCREASE IN CLOUD COVER FROM TONIGHT WILL
LINGER INTO SUNDAY ACROSS MUCH OF THE FORECAST AREA...AS THE LOW
LEVEL INVERSION REMAINS IN PLACE. THIS WILL RESULT IN MOSTLY
CLOUDY SKIES ACROSS ALL AREAS EXCEPT FAR SE. THIS WILL KEEP TEMPS
BELOW THE 1000-0850 THICKNESS FORECAST...BUT COULD BE COMPENSATED
BY THE CONTINUING WARM AIR ADVECTION AND SOME COMPRESSIONAL
HEATING AHEAD OF THE FRONT. WE HAVE OPTED FOR AROUND 50 TO LOWER
50S FOR THE NW ZONES...MID AND UPPER 50S MOST ELSEWHERE...BUT 60
OR LOWER 60S ACROSS THE FAR SE.
INCREASE IN COLD AIR ADVECTION IN WAKE OF THE FRONT SUNDAY NIGHT
WILL ALLOW FOR A STEADY FALL TO TEMPS IN ITS WAKE...BUT WITH FLOW
MORE WEST RATHER THAN NW...WE DO NOT SEE ANYTHING COLDER THAN THE
LOWER AND MID 30S INLAND. NO WINTER TYPE PRECIP CONCERNS AS THE
RAIN ENDS OVERNIGHT BEFORE THE COLDER AIR MOVES IN. WE COULD
HOWEVER BE CONCERNED WITH THE DEVELOPMENT OF BLACK ICE FAR INLAND
AS TEMPS JUST DROP DOWN TO 32 DEGREES...CAUSING LEFTOVER PUDDLES
FROM THE RAIN SUNDAY/SUNDAY EVENING TO FREEZE IN SOME LOCATIONS.
WE WILL ADD MENTION TO THE HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /TONIGHT THROUGH SATURDAY/...
MONDAY THROUGH SATURDAY...MEDIUM RANGE GUIDANCE IN FAIRLY GOOD
AGREEMENT YIELDING HIGHER THAN NORMAL FORECAST CONFIDENCE.
MONDAY THROUGH WEDNESDAY...DESPITE DEEP TROUGHING OVER THE E
COAST...EXPECT A DRY FORECAST WITH THE MAIN AREA OF MOISTURE/LIFT
REMAINING NORTH AND EAST OF THE AREA. HIGHS WILL MAINLY BE IN THE
40S THROUGH THE PERIOD...WITH SOME LOWER 50S ACROSS SE GA. LOWS WILL
BE BELOW NORMAL AS WELL...MAINLY IN THE MID/UPPER 20S AWAY FROM THE
BEACHES.
THURSDAY THROUGH FRIDAY...SLOW MODERATION IN TEMPS AS A SURFACE
HIGH PRESSURE SYSTEM SLIDES BY TO OUR SOUTH CAUSING WINDS TO BECOME
MORE SLY. IN FACT...WE COULD SEE HIGH TEMPS ON FRI REACHING NEAR TO
EVEN SLIGHTLY ABOVE NORMAL LEVELS DESPITE LOW TEMPS REMAINING BELOW
NORMAL. HOWEVER...WE SHOULD REMAIN RAIN-FREE THROUGH THE PERIOD WITH
A LACK OF SIGNIFICANT MOISTURE/LIFT.
FRIDAY NIGHT AND SATURDAY...A COLD FRONT IS EXPECTED TO PUSH INTO
THE AREA LATE IN THE WEEK BRINGING A CHANCE OF SHOWERS...AND
FOLLOWED THE SLOWER ECMWF DUE TO THE ZONAL UPPER FLOW. TEMPS ARE
EXPECTED TO BE NEAR NORMAL.
&&
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
THERE REMAINS A RISK FOR LOW-LEVEL WIND SHEAR /LLWS/ AT THE KSAV
TERMINAL TONIGHT AS SURFACE WINDS REMAIN LIGHT AND 1500 FT WINDS
INCREASE TO AS HIGH AS 30-35 KT AFTER 09Z. 00Z MODEL GUIDANCE HAS
TRENDED SLIGHTLY HIGHER WITH 1500 FT WINDS AT KCHS SO A MENTION OF
LLWS WILL BE EXPANDED TO INCLUDE THE TERMINAL WITH THE 06Z TAF
CYCLE. THE RISK FOR LLWS WILL DIMINISH BY 14Z ONCE THE NOCTURNAL
INVERSION BREAKS AND SURFACE WINDS BEGIN TO INCREASE.
EXTENSIVE MID-LEVEL CLOUDINESS WITH VFR CEILINGS WILL REMAIN
ACROSS THE TERMINALS FOR THE NEXT 12 HOURS BEFORE CEILINGS BEGIN
TO STEADILY FALL BY EARLY AFTERNOON AS A LARGE SWATH OF RAINFALL
APPROACHES FROM THE WEST. BOTH CEILINGS AND VISIBILITIES LOOK TO
DROP TO MVFR THRESHOLDS BY MID AFTERNOON...ROUGHLY AFTER 19Z...
WITH POCKETS OF HEAVIER RAINFALL TEMPORARILY DROPPING CONDITIONS
EVEN LOWER. EXPECT TEMPO IFR AT KCHS BETWEEN 18/21-19/00Z AT KCHS
AND 18/21-19/01Z AT KSAV. FURTHER REFINEMENTS IN BOTH TIMING AND
INTENSITY OF THE HEAVIEST RAINS WILL LIKELY BE NEEDED LATER THIS
MORNING AS SHORT TERM TRENDS BECOME MORE EVIDENT. VFR CONDITIONS
ARE LIKELY TO RETURN BY LATE IN THE PERIOD WITH CLEARING SKIES AT
BOTH TERMINALS.
EXTENDED AVIATION OUTLOOK...VFR CONDITIONS WILL PREVAIL THROUGH
THE PERIOD.
&&
.MARINE...
LIGHT VARIABLE WINDS ACROSS THE MARINE AREA THIS EVENING WILL
BECOME SOUTHWESTERLY OVERNIGHT...AND WITH LOW LEVEL JET AND
GEOSTROPHIC WINDS AT 1000 MB INCREASING...WINDS AND SEAS WILL
BUILD. WIND SPEEDS WILL CLIMB TO NEAR 15 KT LATE. SPEEDS ARE
EXPECTED TO REACH AS HIGH AS 20 KT ACROSS THE NORTHERN CHARLESTON
COUNTY WATERS AND THE OUTER GA WATERS SUNDAY MORNING. WITH THE
FAVORABLE FETCH...SEAS WILL CLIMB TO 3 OR 4 FT LATE.
WE LOOK FOR A FURTHER INCREASE IN BOTH LOW LEVEL WINDS AND 1000 MB
GEOSTROPHIC WINDS...BUT WITH WARM AIR ADVECTION THE MIXING
POTENTIAL WILL BE SOMEWHAT LIMITED. HOWEVER...WE ANTICIPATE AT
LEAST FREQUENT GUSTS TO 25 KT ACROSS AMZ350 AND AMZ374 BY LATE IN
THE DAY...AND THAT ALONG WITH THE SEAS CLIMBING TO AROUND 6 FT HAS
PROMPTED US TO HOIST SCA/S FOR THOSE WATERS STARTING LATE SUNDAY.
CHARLESTON HARBOR WILL BE FLIRTING WITH SCA/S...AS WILL THE OTHER
ATLC WATERS...BUT FOR NOW WE HAVE KEPT JUST BELOW ANY SCA/S ACROSS
AMZ330-352-354.
SW WINDS AHEAD OF THE COLD FRONT SUNDAY EVENING WILL VEER TO
WESTERLY IN ITS WAKE AFTER MIDNIGHT. THE OFFSHORE FETCH WILL LIMIT
SEAS ACROSS THE WATERS OUT 20 NM...BUT THERE WILL STILL BE
FREQUENT GUSTS TO 25 KT ON AMZ350 TO MAINTAIN THE SCA. THE
OFFSHORE FETCH WILL NOT MATTER AS MUCH FOR THE OUTER GA
WATERS...WITH SEAS AS HIGH AS 6 TO 8 FT. WITH INCREASING COLD AIR
ADVECTION THERE WILL BE SOME GUSTS TO NEAR 30 KT. GALES SEEM
RATHER UNFAVORABLE AT THIS TIME.
MONDAY THROUGH THURSDAY...W WINDS WILL REMAIN ELEVATED DUE TO
ENHANCED MIXING WITHIN COLD ADVECTION THROUGH MID WEEK. A SMALL
CRAFT ADVISORY WILL BE IN EFFECT FOR THE NRN SC WATERS THAT WILL
PERSIST INTO MON MORNING...ALTHOUGH THE WINDS OVER THE REMAINING
NEARSHORE WATERS MAY BRIEFLY GET INTO ADVISORY RANGE. THE LINGERING
COLD AIR MASS AND A RELATIVELY TIGHT PRES GRADIENT OVER THE WATERS
WILL MAINTAIN MODERATE OFFSHORE FLOW THROUGH AT LEAST TUE...WITH
ADVISORY CONDITIONS POSSIBLY PERSISTING IN THE GA WATERS BEYOND 20
NM A BIT LONGER. IMPROVING CONDITIONS EXPECTED WED/THU AS HIGH PRES
BUILDS IN FROM THE W AND THE PRES GRADIENT AND COLD AIR ADVECTION
WEAKEN.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EST
TUESDAY FOR AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM THIS AFTERNOON TO 11 AM EST
MONDAY FOR AMZ350.
&&
$$
ST
000
FXUS62 KCHS 180259
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
959 PM EST SAT JAN 17 2009
.SYNOPSIS...
HIGH PRES ACROSS THE AREA THIS EVENING WILL SHIFT SOUTH OF THE
AREA TONIGHT AND SUNDAY. A COLD FRONT WILL MOVE THROUGH LATE
SUNDAY OR SUNDAY NIGHT...WITH A SECONDARY COLD FRONT TO PUSH
THROUGH ON MONDAY. HIGH PRES WILL BUILD INTO THE AREA THROUGH
THURSDAY...WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
00Z CHARLESTON SOUNDING STILL QUITE DRY WITH VERY LOW DEW POINTS
BELOW 850 MB. WARMER AIR SHOWING UP AT 850 MB THIS EVENING WITH
TEMPS NOW GREATER THAN ZERO C.
CLOUDINESS MOVING IN FROM THE W WAS THINNING A BIT AND STARTING
OFF AT ALTOCUMULUS IN THE 9-10 KFT RANGE. VERY FAST SURFACE TEMP
FALLS NOTED AFTER SUNSET THIS EVENING AND OUR FORECAST READINGS
SEEM ON TRACK BY SHOWING COLDER TEMPS THIS EVENING WITH A TREND
FOR SLOW RISES OVERNIGHT WITH THE CLOUDS AND INTENSIFYING WARM
AIR ADVECTION PATTERN OFF THE STABLE SURFACE INVERSION.
REGIONAL RADAR MOSAIC SHOWS SOME LIGHT RADAR RETURNS OVER PARTS OF
N AND W GEORGIA THIS EVENING WHERE SURFACE TEMPERATURES WERE IN
THE UPPER 30S TO LOWER 40S. APPARENTLY LITTLE IF ANY OF THIS WAS
REACHING THE GROUND...HOWEVER A FEW SNOW FLAKES WERE RECENTLY
REPORTED ALONG I-20 TO THE W OF COLUMBIA. A STRONGER SHORT WAVE ON
TAP LATER TONIGHT...PRECIP MAINLY IN THE FORM OF RAIN SHOULD BREAK
OUT TO OUR W LATE. OF COURSE...IF ANYTHING LIGHT REACHES THE GROUND
OVER OUR ZONES LATE IT COULD FREEZE ON CONTACT BUT AT THIS TIME AS
WAS THE CASE TODAY...IT SEEMS DOUBTFUL WITH ALL THE VERY DRY AIR
ALOFT INITIALLY IN PLACE THAT WE WILL SEEM ANY SIGNIFICANT PRECIP
TONIGHT.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
REINFORCING SHORT WAVE INTO THE EASTERN LONG WAVE TROUGH MOVES
INTO THE AREA SUNDAY AFTERNOON AND THROUGH THE AREA SUNDAY
EVENING. ASSOCIATED WITH THIS FEATURE ALOFT IS A SURFACE COLD
FRONT...THAT MOVES INTO THE AREA FROM THE WEST AND NW LATE
SUNDAY...AND THROUGH THE ATLC WATERS EARLY SUNDAY NIGHT.
THERE ARE DEFINITELY DECENT WIND FIELDS ACROSS THE AREA SUNDAY
AFTERNOON AND EVENING...WITH AN UPPER LEVEL JET MAX OF 100-100
KT...LOW LEVEL JET OF 30-40 KT AND A NOTICEABLE INCREASE IN
MOISTURE AS PWATS CLIMB TO NEAR OR OVER AN INCH OVER MOST
LOCATIONS BY 00Z MONDAY. THE RESULT WILL BE FOR AN INCREASING
CHANCE OF SHOWERS FROM WEST TO EAST DURING THE AFTERNOON AND
EVENING HOURS...BEFORE ACTIVITY SHIFTS EAST OF THE AREA BY
MIDNIGHT SUNDAY NIGHT.
THE BEST LIFT...MOISTURE AND CONVERGENCE AHEAD OF THE FRONT DOES
NOT MOVE INTO THE FORECAST AREA UNTIL LATE MORNING OR EARLY
AFTERNOON. THUS WE WILL SHOW ONLY SMALL POPS ACROSS WESTERN AREAS
DURING THE MORNING...BUT RAMP POPS UP FROM WEST TO EAST DURING THE
MID AND LATE AFTERNOON...WITH LIKELY POPS MOST COMMUNITIES EXCEPT
FAR SE SECTIONS. THESE POPS WILL CONTINUE INTO THE EVENING...THEN
TAPER OFF FROM WEST TO EAST IN WAKE OF THE FRONT SUNDAY NIGHT.
MID LEVEL LAPSE RATES ARE MODEST CONSIDERING THE TIME OF THE
YEAR...CLOSE TO 6 DEGREES CELSIUS...BUT THERE IS LITTLE TO NO CAPE
OR INSTABILITY...SO WE ANTICIPATE JUST SHOWERS. MAYBE A FEW
T-STORMS OVER THE GULF STREAM SUNDAY NIGHT AS THE COLD FRONT
APPROACHES...BUT FOR THE MOST PART JUST SHOWERS.
LOOKING AT ABOUT 4-6 HOURS OF PRECIP SUNDAY AFTERNOON AND
EVENING...AND THAT ALONG WITH POPS OF 60-70 PERCENT AND THE
INCREASED IN PWATS WILL RESULT IN ABOUT 1/4 INCH MOST
LOCATIONS...WITH LOCAL AMOUNTS UP TO 1/2 INCH WITH THIS RAIN
EVENT.
TEMPS WILL CERTAINLY BE OF CONCERN SUNDAY...BUT DEFINITELY WARMER
THAN RECENT DAYS. THE INCREASE IN CLOUD COVER FROM TONIGHT WILL
LINGER INTO SUNDAY ACROSS MUCH OF THE FORECAST AREA...AS THE LOW
LEVEL INVERSION REMAINS IN PLACE. THIS WILL RESULT IN MOSTLY
CLOUDY SKIES ACROSS ALL AREAS EXCEPT FAR SE. THIS WILL KEEP TEMPS
BELOW THE 1000-0850 THICKNESS FORECAST...BUT COULD BE COMPENSATED
BY THE CONTINUING WARM AIR ADVECTION AND SOME COMPRESSIONAL
HEATING AHEAD OF THE FRONT. WE HAVE OPTED FOR AROUND 50 TO LOWER
50S FOR THE NW ZONES...MID AND UPPER 50S MOST ELSEWHERE...BUT 60
OR LOWER 60S ACROSS THE FAR SE.
INCREASE IN COLD AIR ADVECTION IN WAKE OF THE FRONT SUNDAY NIGHT
WILL ALLOW FOR A STEADY FALL TO TEMPS IN ITS WAKE...BUT WITH FLOW
MORE WEST RATHER THAN NW...WE DO NOT SEE ANYTHING COLDER THAN THE
LOWER AND MID 30S INLAND. NO WINTER TYPE PRECIP CONCERNS AS THE
RAIN ENDS OVERNIGHT BEFORE THE COLDER AIR MOVES IN. WE COULD
HOWEVER BE CONCERNED WITH THE DEVELOPMENT OF BLACK ICE FAR INLAND
AS TEMPS JUST DROP DOWN TO 32 DEGREES...CAUSING LEFTOVER PUDDLES
FROM THE RAIN SUNDAY/SUNDAY EVENING TO FREEZE IN SOME LOCATIONS.
WE WILL ADD MENTION TO THE HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
MONDAY THROUGH SATURDAY...MEDIUM RANGE GUIDANCE IN FAIRLY GOOD
AGREEMENT YIELDING HIGHER THAN NORMAL FORECAST CONFIDENCE.
MONDAY THROUGH WEDNESDAY...DESPITE DEEP TROUGHING OVER THE E
COAST...EXPECT A DRY FORECAST WITH THE MAIN AREA OF MOISTURE/LIFT
REMAINING NORTH AND EAST OF THE AREA. HIGHS WILL MAINLY BE IN THE
40S THROUGH THE PERIOD...WITH SOME LOWER 50S ACROSS SE GA. LOWS WILL
BE BELOW NORMAL AS WELL...MAINLY IN THE MID/UPPER 20S AWAY FROM THE
BEACHES.
THURSDAY THROUGH FRIDAY...SLOW MODERATION IN TEMPS AS A SURFACE
HIGH PRESSURE SYSTEM SLIDES BY TO OUR SOUTH CAUSING WINDS TO BECOME
MORE SLY. IN FACT...WE COULD SEE HIGH TEMPS ON FRI REACHING NEAR TO
EVEN SLIGHTLY ABOVE NORMAL LEVELS DESPITE LOW TEMPS REMAINING BELOW
NORMAL. HOWEVER...WE SHOULD REMAIN RAIN-FREE THROUGH THE PERIOD WITH
A LACK OF SIGNIFICANT MOISTURE/LIFT.
FRIDAY NIGHT AND SATURDAY...A COLD FRONT IS EXPECTED TO PUSH INTO
THE AREA LATE IN THE WEEK BRINGING A CHANCE OF SHOWERS...AND
FOLLOWED THE SLOWER ECMWF DUE TO THE ZONAL UPPER FLOW. TEMPS ARE
EXPECTED TO BE NEAR NORMAL.
&&
.AVIATION /02Z SUNDAY THROUGH THURSDAY/...
LOW TO MID LEVEL CLOUDS WILL BE ON THE INCREASE OVERNIGHT AT BOTH
TERMINALS AS THE DEVELOPING LOW PRESSURE SYSTEM FROM THE WEST
APPROACHES THE AREA. A LOW LEVEL JET WILL INCREASE TO 25 TO 30 KNOTS
AT 15 KFT AND WITH SURFACE WINDS DECOUPLING HAVE INTRODUCED LOW
LEVEL WIND SHEAR 09-12Z AT KSAV. HAVE LEFT OUT LOW LEVEL WIND
SHEAR AT KCHS AS SOUNDINGS SHOW VERY MARGINAL SOUNDINGS SHOW
MARGINAL WIND SHEAR.
SUNDAY AFTERNOON...A COLD FRONT WILL APPROACH WHICH COULD BRING
SOME SHOWER ACTIVITY AND MVFR CEILINGS LATE IN THE DAY. WITH
UNCERTAINTY IN TIMING AND LOCATION HAVE LEFT OUT OF TAF AT THIS
TIME. WILL REASSESS IN LATER TAF ISSUANCES AS TRENDS BECOME MORE
EVIDENT.
EXTENDED AVIATION OUTLOOK...POSSIBLE MVFR WEATHER WITH SHOWERS
EARLY SUNDAY NIGHT...OTHERWISE VFR CONDITIONS WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
LIGHT VARIABLE WINDS ACROSS THE MARINE AREA THIS EVENING WILL
BECOME SOUTHWESTERLY OVERNIGHT...AND WITH LOW LEVEL JET AND
GEOSTROPHIC WINDS AT 1000 MB INCREASING...WINDS AND SEAS WILL
BUILD. WIND SPEEDS WILL CLIMB TO NEAR 15 KT LATE. SPEEDS ARE
EXPECTED TO REACH AS HIGH AS 20 KT ACROSS THE NORTHERN CHARLESTON
COUNTY WATERS AND THE OUTER GA WATERS SUNDAY MORNING. WITH THE
FAVORABLE FETCH...SEAS WILL CLIMB TO 3 OR 4 FT LATE.
WE LOOK FOR A FURTHER INCREASE IN BOTH LOW LEVEL WINDS AND 1000 MB
GEOSTROPHIC WINDS...BUT WITH WARM AIR ADVECTION THE MIXING
POTENTIAL WILL BE SOMEWHAT LIMITED. HOWEVER...WE ANTICIPATE AT
LEAST FREQUENT GUSTS TO 25 KT ACROSS AMZ350 AND AMZ374 BY LATE IN
THE DAY...AND THAT ALONG WITH THE SEAS CLIMBING TO AROUND 6 FT HAS
PROMPTED US TO HOIST SCA/S FOR THOSE WATERS STARTING LATE SUNDAY.
CHARLESTON HARBOR WILL BE FLIRTING WITH SCA/S...AS WILL THE OTHER
ATLC WATERS...BUT FOR NOW WE HAVE KEPT JUST BELOW ANY SCA/S ACROSS
AMZ330-352-354.
SW WINDS AHEAD OF THE COLD FRONT SUNDAY EVENING WILL VEER TO
WESTERLY IN ITS WAKE AFTER MIDNIGHT. THE OFFSHORE FETCH WILL LIMIT
SEAS ACROSS THE WATERS OUT 20 NM...BUT THERE WILL STILL BE
FREQUENT GUSTS TO 25 KT ON AMZ350 TO MAINTAIN THE SCA. THE
OFFSHORE FETCH WILL NOT MATTER AS MUCH FOR THE OUTER GA
WATERS...WITH SEAS AS HIGH AS 6 TO 8 FT. WITH INCREASING COLD AIR
ADVECTION THERE WILL BE SOME GUSTS TO NEAR 30 KT. GALES SEEM
RATHER UNFAVORABLE AT THIS TIME.
MONDAY THROUGH THURSDAY...W WINDS WILL REMAIN ELEVATED DUE TO
ENHANCED MIXING WITHIN COLD ADVECTION THROUGH MID WEEK. A SMALL
CRAFT ADVISORY WILL BE IN EFFECT FOR THE NRN SC WATERS THAT WILL
PERSIST INTO MON MORNING...ALTHOUGH THE WINDS OVER THE REMAINING
NEARSHORE WATERS MAY BRIEFLY GET INTO ADVISORY RANGE. THE LINGERING
COLD AIR MASS AND A RELATIVELY TIGHT PRES GRADIENT OVER THE WATERS
WILL MAINTAIN MODERATE OFFSHORE FLOW THROUGH AT LEAST TUE...WITH
ADVISORY CONDITIONS POSSIBLY PERSISTING IN THE GA WATERS BEYOND 20
NM A BIT LONGER. IMPROVING CONDITIONS EXPECTED WED/THU AS HIGH PRES
BUILDS IN FROM THE W AND THE PRES GRADIENT AND COLD AIR ADVECTION
WEAKEN.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 11 AM EST TUESDAY FOR
AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 11 AM EST MONDAY FOR
AMZ350.
&&
$$
000
FXUS62 KCHS 172343
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
643 PM EST SAT JAN 17 2009
.SYNOPSIS...
HIGH PRES ACROSS THE AREA THIS EVENING WILL SHIFT SOUTH OF THE
AREA TONIGHT AND SUNDAY. A COLD FRONT WILL MOVE THROUGH LATE
SUNDAY OR SUNDAY NIGHT...WITH A SECONDARY COLD FRONT TO PUSH
THROUGH ON MONDAY. HIGH PRES WILL BUILD INTO THE AREA THROUGH
THURSDAY...WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
HIGH PRES ACROSS THE LOCAL AREA WITH LIGHT WINDS AND CLEAR SKIES
THIS EVENING WILL RESULT IN A QUICK DROP TO TEMPS AWAY FROM THE
COAST...WITH DEW POINTS DOWN IN THE SINGLE NUMBERS AND TEENS AS OF
LATE AFTERNOON. LOOK FOR MOST LOCATIONS WEST OF THE INTRACOASTAL
TO FALL BELOW FREEZING BY 7-9 PM WITH THE RADIATIONAL
COOLING...AND MANY AREAS WILL SEE LOW TEMPS EARLY TONIGHT IN THE
MID AND UPPER 20S. HOWEVER...TEMPS WILL HOLD STEADY OR EVEN RISE
THROUGH THE OVERNIGHT HOURS. WEAK SHORT WAVE NOW MOVING THROUGH
ALABAMA WILL SHIFT QUICKLY EAST...WHILE A STRONGER SHORT WAVE
MOVES INTO THE MID AND LOWER MS VALLEY THROUGH THE NIGHT. THIS
SHARPENS THE LONG WAVE TROUGH ACROSS THE EASTERN
STATES...RESULTING IN AN INCREASE OF LOW LEVEL WINDS AND A 30-40
KT LOW LEVEL JET TRAVERSING THE AREA AFTER MIDNIGHT. THE FIRST
SHORT WAVE WILL ALLOW FOR SOME OF THOSE THICK STRATOCUMULUS AND
ALTOCUMULUS CLOUDS NOW MOVING INTO WESTERN GA TO OVERSPREAD THE
AREA BY MIDNIGHT. ISENTROPIC LIFT ALSO INCREASES THROUGH THE NIGHT
IN ASSOCIATION WITH THE LOW LEVEL JET...THUS WE LOOK FOR
INCREASING CLOUDINESS AFTER MOSTLY CLEAR SKIES THIS EVENING. THE
INCREASED CLOUD COVER...A MODERATELY MIXED BOUNDARY LAYER AND
INCREASING WARM AIR ADVECTION WILL CAUSE TEMPS TO CLIMB ABOVE
FREEZING JUST ABOUT EVERYWHERE BEFORE DAYBREAK SUNDAY. SHOULD THE
TIMING OF THE CLOUD COVER BE ALTERED...WE ANTICIPATE SKIES
BECOMING PARTLY TO MOSTLY CLOUDY BY 03-06Z...THEN TEMPS WOULD BE
AFFECTED.
ALTHOUGH THERE IS STILL PLENTY OF DRY AIR LATE TONIGHT AND WET
BULBS NEAR OR SLIGHTLY BELOW FREEZING ACROSS THE NW TIER...WE DO
NOT ANTICIPATE ANY PRECIP TONIGHT. THUS THERE ARE NO CONCERNS
ABOUT ANY WINTER TYPE PRECIP LATE TONIGHT.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
REINFORCING SHORT WAVE INTO THE EASTERN LONG WAVE TROUGH MOVES
INTO THE AREA SUNDAY AFTERNOON AND THROUGH THE AREA SUNDAY
EVENING. ASSOCIATED WITH THIS FEATURE ALOFT IS A SURFACE COLD
FRONT...THAT MOVES INTO THE AREA FROM THE WEST AND NW LATE
SUNDAY...AND THROUGH THE ATLC WATERS EARLY SUNDAY NIGHT.
THERE ARE DEFINITELY DECENT WIND FIELDS ACROSS THE AREA SUNDAY
AFTERNOON AND EVENING...WITH AN UPPER LEVEL JET MAX OF 100-100
KT...LOW LEVEL JET OF 30-40 KT AND A NOTICEABLE INCREASE IN
MOISTURE AS PWATS CLIMB TO NEAR OR OVER AN INCH OVER MOST
LOCATIONS BY 00Z MONDAY. THE RESULT WILL BE FOR AN INCREASING
CHANCE OF SHOWERS FROM WEST TO EAST DURING THE AFTERNOON AND
EVENING HOURS...BEFORE ACTIVITY SHIFTS EAST OF THE AREA BY
MIDNIGHT SUNDAY NIGHT.
THE BEST LIFT...MOISTURE AND CONVERGENCE AHEAD OF THE FRONT DOES
NOT MOVE INTO THE FORECAST AREA UNTIL LATE MORNING OR EARLY
AFTERNOON. THUS WE WILL SHOW ONLY SMALL POPS ACROSS WESTERN AREAS
DURING THE MORNING...BUT RAMP POPS UP FROM WEST TO EAST DURING THE
MID AND LATE AFTERNOON...WITH LIKELY POPS MOST COMMUNITIES EXCEPT
FAR SE SECTIONS. THESE POPS WILL CONTINUE INTO THE EVENING...THEN
TAPER OFF FROM WEST TO EAST IN WAKE OF THE FRONT SUNDAY NIGHT.
MID LEVEL LAPSE RATES ARE MODEST CONSIDERING THE TIME OF THE
YEAR...CLOSE TO 6 DEGREES CELSIUS...BUT THERE IS LITTLE TO NO CAPE
OR INSTABILITY...SO WE ANTICIPATE JUST SHOWERS. MAYBE A FEW
T-STORMS OVER THE GULF STREAM SUNDAY NIGHT AS THE COLD FRONT
APPROACHES...BUT FOR THE MOST PART JUST SHOWERS.
LOOKING AT ABOUT 4-6 HOURS OF PRECIP SUNDAY AFTERNOON AND
EVENING...AND THAT ALONG WITH POPS OF 60-70 PERCENT AND THE
INCREASED IN PWATS WILL RESULT IN ABOUT 1/4 INCH MOST
LOCATIONS...WITH LOCAL AMOUNTS UP TO 1/2 INCH WITH THIS RAIN
EVENT.
TEMPS WILL CERTAINLY BE OF CONCERN SUNDAY...BUT DEFINITELY WARMER
THAN RECENT DAYS. THE INCREASE IN CLOUD COVER FROM TONIGHT WILL
LINGER INTO SUNDAY ACROSS MUCH OF THE FORECAST AREA...AS THE LOW
LEVEL INVERSION REMAINS IN PLACE. THIS WILL RESULT IN MOSTLY
CLOUDY SKIES ACROSS ALL AREAS EXCEPT FAR SE. THIS WILL KEEP TEMPS
BELOW THE 1000-0850 THICKNESS FORECAST...BUT COULD BE COMPENSATED
BY THE CONTINUING WARM AIR ADVECTION AND SOME COMPRESSIONAL
HEATING AHEAD OF THE FRONT. WE HAVE OPTED FOR AROUND 50 TO LOWER
50S FOR THE NW ZONES...MID AND UPPER 50S MOST ELSEWHERE...BUT 60
OR LOWER 60S ACROSS THE FAR SE.
INCREASE IN COLD AIR ADVECTION IN WAKE OF THE FRONT SUNDAY NIGHT
WILL ALLOW FOR A STEADY FALL TO TEMPS IN ITS WAKE...BUT WITH FLOW
MORE WEST RATHER THAN NW...WE DO NOT SEE ANYTHING COLDER THAN THE
LOWER AND MID 30S INLAND. NO WINTER TYPE PRECIP CONCERNS AS THE
RAIN ENDS OVERNIGHT BEFORE THE COLDER AIR MOVES IN. WE COULD
HOWEVER BE CONCERNED WITH THE DEVELOPMENT OF BLACK ICE FAR INLAND
AS TEMPS JUST DROP DOWN TO 32 DEGREES...CAUSING LEFTOVER PUDDLES
FROM THE RAIN SUNDAY/SUNDAY EVENING TO FREEZE IN SOME LOCATIONS.
WE WILL ADD MENTION TO THE HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
MONDAY THROUGH SATURDAY...MEDIUM RANGE GUIDANCE IN FAIRLY GOOD
AGREEMENT YIELDING HIGHER THAN NORMAL FORECAST CONFIDENCE.
MONDAY THROUGH WEDNESDAY...DESPITE DEEP TROUGHING OVER THE E
COAST...EXPECT A DRY FORECAST WITH THE MAIN AREA OF MOISTURE/LIFT
REMAINING NORTH AND EAST OF THE AREA. HIGHS WILL MAINLY BE IN THE
40S THROUGH THE PERIOD...WITH SOME LOWER 50S ACROSS SE GA. LOWS WILL
BE BELOW NORMAL AS WELL...MAINLY IN THE MID/UPPER 20S AWAY FROM THE
BEACHES.
THURSDAY THROUGH FRIDAY...SLOW MODERATION IN TEMPS AS A SURFACE
HIGH PRESSURE SYSTEM SLIDES BY TO OUR SOUTH CAUSING WINDS TO BECOME
MORE SLY. IN FACT...WE COULD SEE HIGH TEMPS ON FRI REACHING NEAR TO
EVEN SLIGHTLY ABOVE NORMAL LEVELS DESPITE LOW TEMPS REMAINING BELOW
NORMAL. HOWEVER...WE SHOULD REMAIN RAIN-FREE THROUGH THE PERIOD WITH
A LACK OF SIGNIFICANT MOISTURE/LIFT.
FRIDAY NIGHT AND SATURDAY...A COLD FRONT IS EXPECTED TO PUSH INTO
THE AREA LATE IN THE WEEK BRINGING A CHANCE OF SHOWERS...AND
FOLLOWED THE SLOWER ECMWF DUE TO THE ZONAL UPPER FLOW. TEMPS ARE
EXPECTED TO BE NEAR NORMAL.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
LOW TO MID LEVEL CLOUDS WILL BE ON THE INCREASE OVERNIGHT AT BOTH
TERMINALS AS THE DEVELOPING LOW PRESSURE SYSTEM FROM THE WEST
APPROACHES THE AREA. A LOW LEVEL JET WILL INCREASE TO 25 TO 30 KNOTS
AT 15 KFT AND WITH SURFACE WINDS DECOUPLING HAVE INTRODUCED LOW
LEVEL WIND SHEAR 09-12Z AT KSAV. HAVE LEFT OUT LOW LEVEL WIND
SHEAR AT KCHS AS SOUNDINGS SHOW VERY MARGINAL SOUNDINGS SHOW
MARGINAL WIND SHEAR.
SUNDAY AFTERNOON...A COLD FRONT WILL APPROACH WHICH COULD BRING
SOME SHOWER ACTIVITY AND MVFR CEILINGS LATE IN THE DAY. WITH
UNCERTAINTY IN TIMING AND LOCATION HAVE LEFT OUT OF TAF AT THIS
TIME. WILL REASSESS IN LATER TAF ISSUANCES AS TRENDS BECOME MORE
EVIDENT.
EXTENDED AVIATION OUTLOOK...POSSIBLE MVFR WEATHER WITH SHOWERS
EARLY SUNDAY NIGHT...OTHERWISE VFR CONDITIONS WILL PREVAIL
THROUGH THE PERIOD.
&&
.MARINE...
LIGHT WINDS ACROSS THE MARINE AREA THIS EVENING WILL BECOME
SOUTHWESTERLY OVERNIGHT...AND WITH LOW LEVEL JET AND GEOSTROPHIC
WINDS AT 1000 MB INCREASING...WINDS AND SEAS WILL BUILD. WIND
SPEEDS WILL CLIMB TO AT LEAST 15 KT LATE...BUT AS HIGH AS 20 KT
ACROSS THE NORTHERN CHARLESTON COUNTY WATERS AND THE OUTER GA
WATERS BEFORE MORNING. WITH THE FAVORABLE FETCH...SEAS WILL CLIMB
TO 4 OR 5 FT AFTER MIDNIGHT.
WE LOOK FOR A FURTHER INCREASE IN BOTH LOW LEVEL WINDS AND 1000 MB
GEOSTROPHIC WINDS...BUT WITH WARM AIR ADVECTION THE MIXING
POTENTIAL WILL BE SOMEWHAT LIMITED. HOWEVER...WE ANTICIPATE AT
LEAST FREQUENT GUSTS TO 25 KT ACROSS AMZ350 AND AMZ374 BY LATE IN
THE DAY...AND THAT ALONG WITH THE SEAS CLIMBING TO AROUND 6 FT HAS
PROMPTED US TO HOIST SCA/S FOR THOSE WATERS STARTING LATE SUNDAY.
CHARLESTON HARBOR WILL BE FLIRTING WITH SCA/S...AS WILL THE OTHER
ATLC WATERS...BUT FOR NOW WE HAVE KEPT JUST BELOW ANY SCA/S ACROSS
AMZ330-352-354.
SW WINDS AHEAD OF THE COLD FRONT SUNDAY EVENING WILL VEER TO
WESTERLY IN ITS WAKE AFTER MIDNIGHT. THE OFFSHORE FETCH WILL LIMIT
SEAS ACROSS THE WATERS OUT 20 NM...BUT THERE WILL STILL BE
FREQUENT GUSTS TO 25 KT ON AMZ350 TO MAINTAIN THE SCA. THE
OFFSHORE FETCH WILL NOT MATTER AS MUCH FOR THE OUTER GA
WATERS...WITH SEAS AS HIGH AS 6 TO 8 FT. WITH INCREASING COLD AIR
ADVECTION THERE WILL BE SOME GUSTS TO NEAR 30 KT. GALES SEEM
RATHER UNFAVORABLE AT THIS TIME.
MONDAY THROUGH THURSDAY...W WINDS WILL REMAIN ELEVATED DUE TO
ENHANCED MIXING WITHIN COLD ADVECTION THROUGH MID WEEK. A SMALL
CRAFT ADVISORY WILL BE IN EFFECT FOR THE NRN SC WATERS THAT WILL
PERSIST INTO MON MORNING...ALTHOUGH THE WINDS OVER THE REMAINING
NEARSHORE WATERS MAY BRIEFLY GET INTO ADVISORY RANGE. THE LINGERING
COLD AIR MASS AND A RELATIVELY TIGHT PRES GRADIENT OVER THE WATERS
WILL MAINTAIN MODERATE OFFSHORE FLOW THROUGH AT LEAST TUE...WITH
ADVISORY CONDITIONS POSSIBLY PERSISTING IN THE GA WATERS BEYOND 20
NM A BIT LONGER. IMPROVING CONDITIONS EXPECTED WED/THU AS HIGH PRES
BUILDS IN FROM THE W AND THE PRES GRADIENT AND COLD AIR ADVECTION
WEAKEN.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 11 AM EST TUESDAY FOR
AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 11 AM EST MONDAY FOR
AMZ350.
&&
$$
000
FXUS62 KCHS 172114
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
414 PM EST SAT JAN 17 2009
.SYNOPSIS...
HIGH PRES ACROSS THE AREA THIS EVENING WILL SHIFT SOUTH OF THE
AREA TONIGHT AND SUNDAY. A COLD FRONT WILL MOVE THROUGH LATE
SUNDAY OR SUNDAY NIGHT...WITH A SECONDARY COLD FRONT TO PUSH
THROUGH ON MONDAY. HIGH PRES WILL BUILD INTO THE AREA THROUGH
THURSDAY...WITH ANOTHER COLD FRONT POSSIBLE LATE IN THE WEEK.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
HIGH PRES ACROSS THE LOCAL AREA WITH LIGHT WINDS AND CLEAR SKIES
THIS EVENING WILL RESULT IN A QUICK DROP TO TEMPS AWAY FROM THE
COAST...WITH DEW POINTS DOWN IN THE SINGLE NUMBERS AND TEENS AS OF
LATE AFTERNOON. LOOK FOR MOST LOCATIONS WEST OF THE INTRACOASTAL
TO FALL BELOW FREEZING BY 7-9 PM WITH THE RADIATIONAL
COOLING...AND MANY AREAS WILL SEE LOW TEMPS EARLY TONIGHT IN THE
MID AND UPPER 20S. HOWEVER...TEMPS WILL HOLD STEADY OR EVEN RISE
THROUGH THE OVERNIGHT HOURS. WEAK SHORT WAVE NOW MOVING THROUGH
ALABAMA WILL SHIFT QUICKLY EAST...WHILE A STRONGER SHORT WAVE
MOVES INTO THE MID AND LOWER MS VALLEY THROUGH THE NIGHT. THIS
SHARPENS THE LONG WAVE TROUGH ACROSS THE EASTERN
STATES...RESULTING IN AN INCREASE OF LOW LEVEL WINDS AND A 30-40
KT LOW LEVEL JET TRAVERSING THE AREA AFTER MIDNIGHT. THE FIRST
SHORT WAVE WILL ALLOW FOR SOME OF THOSE THICK STRATOCUMULUS AND
ALTOCUMULUS CLOUDS NOW MOVING INTO WESTERN GA TO OVERSPREAD THE
AREA BY MIDNIGHT. ISENTROPIC LIFT ALSO INCREASES THROUGH THE NIGHT
IN ASSOCIATION WITH THE LOW LEVEL JET...THUS WE LOOK FOR
INCREASING CLOUDINESS AFTER MOSTLY CLEAR SKIES THIS EVENING. THE
INCREASED CLOUD COVER...A MODERATELY MIXED BOUNDARY LAYER AND
INCREASING WARM AIR ADVECTION WILL CAUSE TEMPS TO CLIMB ABOVE
FREEZING JUST ABOUT EVERYWHERE BEFORE DAYBREAK SUNDAY. SHOULD THE
TIMING OF THE CLOUD COVER BE ALTERED...WE ANTICIPATE SKIES
BECOMING PARTLY TO MOSTLY CLOUDY BY 03-06Z...THEN TEMPS WOULD BE
AFFECTED.
ALTHOUGH THERE IS STILL PLENTY OF DRY AIR LATE TONIGHT AND WET
BULBS NEAR OR SLIGHTLY BELOW FREEZING ACROSS THE NW TIER...WE DO
NOT ANTICIPATE ANY PRECIP TONIGHT. THUS THERE ARE NO CONCERNS
ABOUT ANY WINTER TYPE PRECIP LATE TONIGHT.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
REINFORCING SHORT WAVE INTO THE EASTERN LONG WAVE TROUGH MOVES
INTO THE AREA SUNDAY AFTERNOON AND THROUGH THE AREA SUNDAY
EVENING. ASSOCIATED WITH THIS FEATURE ALOFT IS A SURFACE COLD
FRONT...THAT MOVES INTO THE AREA FROM THE WEST AND NW LATE
SUNDAY...AND THROUGH THE ATLC WATERS EARLY SUNDAY NIGHT.
THERE ARE DEFINITELY DECENT WIND FIELDS ACROSS THE AREA SUNDAY
AFTERNOON AND EVENING...WITH AN UPPER LEVEL JET MAX OF 100-100
KT...LOW LEVEL JET OF 30-40 KT AND A NOTICEABLE INCREASE IN
MOISTURE AS PWATS CLIMB TO NEAR OR OVER AN INCH OVER MOST
LOCATIONS BY 00Z MONDAY. THE RESULT WILL BE FOR AN INCREASING
CHANCE OF SHOWERS FROM WEST TO EAST DURING THE AFTERNOON AND
EVENING HOURS...BEFORE ACTIVITY SHIFTS EAST OF THE AREA BY
MIDNIGHT SUNDAY NIGHT.
THE BEST LIFT...MOISTURE AND CONVERGENCE AHEAD OF THE FRONT DOES
NOT MOVE INTO THE FORECAST AREA UNTIL LATE MORNING OR EARLY
AFTERNOON. THUS WE WILL SHOW ONLY SMALL POPS ACROSS WESTERN AREAS
DURING THE MORNING...BUT RAMP POPS UP FROM WEST TO EAST DURING THE
MID AND LATE AFTERNOON...WITH LIKELY POPS MOST COMMUNITIES EXCEPT
FAR SE SECTIONS. THESE POPS WILL CONTINUE INTO THE EVENING...THEN
TAPER OFF FROM WEST TO EAST IN WAKE OF THE FRONT SUNDAY NIGHT.
MID LEVEL LAPSE RATES ARE MODEST CONSIDERING THE TIME OF THE
YEAR...CLOSE TO 6 DEGREES CELSIUS...BUT THERE IS LITTLE TO NO CAPE
OR INSTABILITY...SO WE ANTICIPATE JUST SHOWERS. MAYBE A FEW
T-STORMS OVER THE GULF STREAM SUNDAY NIGHT AS THE COLD FRONT
APPROACHES...BUT FOR THE MOST PART JUST SHOWERS.
LOOKING AT ABOUT 4-6 HOURS OF PRECIP SUNDAY AFTERNOON AND
EVENING...AND THAT ALONG WITH POPS OF 60-70 PERCENT AND THE
INCREASED IN PWATS WILL RESULT IN ABOUT 1/4 INCH MOST
LOCATIONS...WITH LOCAL AMOUNTS UP TO 1/2 INCH WITH THIS RAIN
EVENT.
TEMPS WILL CERTAINLY BE OF CONCERN SUNDAY...BUT DEFINITELY WARMER
THAN RECENT DAYS. THE INCREASE IN CLOUD COVER FROM TONIGHT WILL
LINGER INTO SUNDAY ACROSS MUCH OF THE FORECAST AREA...AS THE LOW
LEVEL INVERSION REMAINS IN PLACE. THIS WILL RESULT IN MOSTLY
CLOUDY SKIES ACROSS ALL AREAS EXCEPT FAR SE. THIS WILL KEEP TEMPS
BELOW THE 1000-0850 THICKNESS FORECAST...BUT COULD BE COMPENSATED
BY THE CONTINUING WARM AIR ADVECTION AND SOME COMPRESSIONAL
HEATING AHEAD OF THE FRONT. WE HAVE OPTED FOR AROUND 50 TO LOWER
50S FOR THE NW ZONES...MID AND UPPER 50S MOST ELSEWHERE...BUT 60
OR LOWER 60S ACROSS THE FAR SE.
INCREASE IN COLD AIR ADVECTION IN WAKE OF THE FRONT SUNDAY NIGHT
WILL ALLOW FOR A STEADY FALL TO TEMPS IN ITS WAKE...BUT WITH FLOW
MORE WEST RATHER THAN NW...WE DO NOT SEE ANYTHING COLDER THAN THE
LOWER AND MID 30S INLAND. NO WINTER TYPE PRECIP CONCERNS AS THE
RAIN ENDS OVERNIGHT BEFORE THE COLDER AIR MOVES IN. WE COULD
HOWEVER BE CONCERNED WITH THE DEVELOPMENT OF BLACK ICE FAR INLAND
AS TEMPS JUST DROP DOWN TO 32 DEGREES...CAUSING LEFTOVER PUDDLES
FROM THE RAIN SUNDAY/SUNDAY EVENING TO FREEZE IN SOME LOCATIONS.
WE WILL ADD MENTION TO THE HAZARDOUS WEATHER OUTLOOK.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
MONDAY THROUGH SATURDAY...MEDIUM RANGE GUIDANCE IN FAIRLY GOOD
AGREEMENT YIELDING HIGHER THAN NORMAL FORECAST CONFIDENCE.
MONDAY THROUGH WEDNESDAY...DESPITE DEEP TROUGHING OVER THE E
COAST...EXPECT A DRY FORECAST WITH THE MAIN AREA OF MOISTURE/LIFT
REMAINING NORTH AND EAST OF THE AREA. HIGHS WILL MAINLY BE IN THE
40S THROUGH THE PERIOD...WITH SOME LOWER 50S ACROSS SE GA. LOWS WILL
BE BELOW NORMAL AS WELL...MAINLY IN THE MID/UPPER 20S AWAY FROM THE
BEACHES.
THURSDAY THROUGH FRIDAY...SLOW MODERATION IN TEMPS AS A SURFACE
HIGH PRESSURE SYSTEM SLIDES BY TO OUR SOUTH CAUSING WINDS TO BECOME
MORE SLY. IN FACT...WE COULD SEE HIGH TEMPS ON FRI REACHING NEAR TO
EVEN SLIGHTLY ABOVE NORMAL LEVELS DESPITE LOW TEMPS REMAINING BELOW
NORMAL. HOWEVER...WE SHOULD REMAIN RAIN-FREE THROUGH THE PERIOD WITH
A LACK OF SIGNIFICANT MOISTURE/LIFT.
FRIDAY NIGHT AND SATURDAY...A COLD FRONT IS EXPECTED TO PUSH INTO
THE AREA LATE IN THE WEEK BRINGING A CHANCE OF SHOWERS...AND
FOLLOWED THE SLOWER ECMWF DUE TO THE ZONAL UPPER FLOW. TEMPS ARE
EXPECTED TO BE NEAR NORMAL.
&&
.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
VFR CONDITIONS WILL PREVAIL FOR THE NEXT 24 HOUR PERIOD AT BOTH KCHS
AND KSAV. EXPECT NORTHEASTERLY WINDS TO VEER TO THE SOUTH BY
SATURDAY EVENING...WITH SOUTHWESTERLY WINDS PREVAILING AT BOTH
TERMINALS ON SUNDAY. VFR CLOUD COVERAGE WILL INCREASE OVERNIGHT AS
ISENTROPIC LIFT ASSOCIATED WITH A DEVELOPING LOW APPROACHES FROM
THE WEST. SOME LLWS IS POSSIBLE AROUND SUNRISE SUNDAY MORNING AS
SOUNDINGS SHOWING 25 TO 30 KNOT WINDS AROUND 2000 FT...ESPECIALLY
FOR KCHS. YET WITH WINDS REMAINING SOUTHWESTERLY AT THIS
LEVEL...HAVE EXCLUDED THIS FROM EITHER TAF AS LLWS IS EXPECTED TO
REMAIN MARGINAL.
EXTENDED AVIATION OUTLOOK...POSSIBLE MVFR WEATHER WITH SHOWERS
LATE SUNDAY/EARLY SUNDAY NIGHT...OTHERWISE VFR CONDITIONS WILL
PREVAIL THROUGH THE PERIOD.
&&
.MARINE...
LIGHT WINDS ACROSS THE MARINE AREA THIS EVENING WILL BECOME
SOUTHWESTERLY OVERNIGHT...AND WITH LOW LEVEL JET AND GEOSTROPHIC
WINDS AT 1000 MB INCREASING...WINDS AND SEAS WILL BUILD. WIND
SPEEDS WILL CLIMB TO AT LEAST 15 KT LATE...BUT AS HIGH AS 20 KT
ACROSS THE NORTHERN CHARLESTON COUNTY WATERS AND THE OUTER GA
WATERS BEFORE MORNING. WITH THE FAVORABLE FETCH...SEAS WILL CLIMB
TO 4 OR 5 FT AFTER MIDNIGHT.
WE LOOK FOR A FURTHER INCREASE IN BOTH LOW LEVEL WINDS AND 1000 MB
GEOSTROPHIC WINDS...BUT WITH WARM AIR ADVECTION THE MIXING
POTENTIAL WILL BE SOMEWHAT LIMITED. HOWEVER...WE ANTICIPATE AT
LEAST FREQUENT GUSTS TO 25 KT ACROSS AMZ350 AND AMZ374 BY LATE IN
THE DAY...AND THAT ALONG WITH THE SEAS CLIMBING TO AROUND 6 FT HAS
PROMPTED US TO HOIST SCA/S FOR THOSE WATERS STARTING LATE SUNDAY.
CHARLESTON HARBOR WILL BE FLIRTING WITH SCA/S...AS WILL THE OTHER
ATLC WATERS...BUT FOR NOW WE HAVE KEPT JUST BELOW ANY SCA/S ACROSS
AMZ330-352-354.
SW WINDS AHEAD OF THE COLD FRONT SUNDAY EVENING WILL VEER TO
WESTERLY IN ITS WAKE AFTER MIDNIGHT. THE OFFSHORE FETCH WILL LIMIT
SEAS ACROSS THE WATERS OUT 20 NM...BUT THERE WILL STILL BE
FREQUENT GUSTS TO 25 KT ON AMZ350 TO MAINTAIN THE SCA. THE
OFFSHORE FETCH WILL NOT MATTER AS MUCH FOR THE OUTER GA
WATERS...WITH SEAS AS HIGH AS 6 TO 8 FT. WITH INCREASING COLD AIR
ADVECTION THERE WILL BE SOME GUSTS TO NEAR 30 KT. GALES SEEM
RATHER UNFAVORABLE AT THIS TIME.
MONDAY THROUGH THURSDAY...W WINDS WILL REMAIN ELEVATED DUE TO
ENHANCED MIXING WITHIN COLD ADVECTION THROUGH MID WEEK. A SMALL
CRAFT ADVISORY WILL BE IN EFFECT FOR THE NRN SC WATERS THAT WILL
PERSIST INTO MON MORNING...ALTHOUGH THE WINDS OVER THE REMAINING
NEARSHORE WATERS MAY BRIEFLY GET INTO ADVISORY RANGE. THE LINGERING
COLD AIR MASS AND A RELATIVELY TIGHT PRES GRADIENT OVER THE WATERS
WILL MAINTAIN MODERATE OFFSHORE FLOW THROUGH AT LEAST TUE...WITH
ADVISORY CONDITIONS POSSIBLY PERSISTING IN THE GA WATERS BEYOND 20
NM A BIT LONGER. IMPROVING CONDITIONS EXPECTED WED/THU AS HIGH PRES
BUILDS IN FROM THE W AND THE PRES GRADIENT AND COLD AIR ADVECTION
WEAKEN.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 11 AM EST TUESDAY FOR
AMZ374.
SMALL CRAFT ADVISORY FROM 4 PM SUNDAY TO 11 AM EST MONDAY FOR
AMZ350.
&&
$$
33/44
000
FXUS62 KCHS 171740
AFDCHS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHARLESTON SC
1240 PM EST SAT JAN 17 2009
.SYNOPSIS...
ARCTIC HIGH PRESSURE WILL REMAIN ACROSS THE REGION TODAY...THEN
SHIFT SOUTH TONIGHT. A COLD FRONT WILL MOVE THROUGH THE AREA LATE
SUNDAY...THEN HIGH PRESSURE BUILDS BACK OVER THE REGION INTO LATE
NEXT WEEK.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
TEMPS ARE STILL STRUGGLING TO RISE ABOVE FREEZING THIS MORNING
DESPITE THE FULL SUNSHINE ACROSS THE FORECAST AREA.
HOWEVER...TEMPS WILL TURN OUT TO BE SEVERAL DEGREES WARMER THAN
YESTERDAY AS COLD AIR ADVECTION ENDS AND AIR MASS MODERATES WITH
LOW LEVEL FLOW VEERING TO EASTERLY THIS AFTERNOON. THE 1000-850
THICKNESS FORECAST SUPPORTS ONLY UPPER 30S FAR NORTH TO UPPER 40S
FAR SOUTH...AND SINCE ACTUAL TEMPS ARE STILL BELOW 15Z MOS
GUIDANCE TEMPS IN SOME LOCATIONS...WE WILL DROP TEMPS OVER THE FAR
NORTHERN AREAS A FEW DEGREES TO BETTER MESH WITH THICKNESS
FORECAST. COMPARED TO SEASONAL LEVELS...THIS WILL BE ABOUT 12-18
DEGREES COLDER THAN NORMAL.
COLD AIR STRATOCUMULUS WILL REMAIN OVER THE ATLC TODAY...WITH A
FEW MAKING A RUN FOR THE COAST LATE AS FLOW VEERS TO ONSHORE. BUT
WITH LARGE DEW POINT DEPRESSIONS WE SEE NO REASON TO DEVIATE FROM
A MOSTLY SUNNY OR SUNNY FORECAST THIS AFTERNOON...AS MID AND HIGH
CLOUDS STAY MAINLY NORTH AND WEST THROUGH THE DAY.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
A MUCH STRONGER SHORTWAVE WILL ROUND THE BASE OF THE LONG-WAVE
TROUGH TONIGHT AS THE REMNANTS OF THE ARCTIC HIGH SHIFT EVEN
FARTHER TO THE SOUTH INTO THE GULF OF MEXICO AND CENTRAL FLORIDA.
AS THE TROUGH DIGS THROUGH THE MIDDLE MISSISSIPPI VALLEY IT WILL
INDUCE THE FORMATION OF A 20-30 KT NOCTURNAL JET ACROSS THE
REGION. WEAK 290K ISENTROPIC LIFT ASSOCIATED WITH THE NOCTURNAL
JET WILL SUPPORT THE GENESIS OF A RATHER EXTENSIVE MID-LEVEL
CLOUD DECK ACROSS THE DEEP SOUTH TONIGHT...WHICH WILL MOVE
STEADILY EASTWARD INTO THE FORECAST AREA AFTER MIDNIGHT. INCREASED
CLOUD COVER COUPLED WITH A WEAKLY MIXED BOUNDARY LAYER WILL
SUPPORT WARMER OVERNIGHT LOWS...RANGING FROM THE UPPER 20S WELL
INLAND WITH MID 30S CLOSER TO THE IMMEDIATE COAST. FURTHER
REFINEMENTS IN TONIGHT/S LOWS WILL BE NEEDED LATER TODAY...
PARTICULARLY IF THE TIMING AND/OR CHARACTER OF THE INCOMING CLOUD
DECK TONIGHT CHANGES.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
MODELS ARE IN GOOD AGREEMENT REGARDING THE TIMING AND EFFECTS OF A
COLD FRONT PUSHING THROUGH THE REGION ON SUNDAY. GFS...NAM AND
ECMWF MODELS ALL SUGGEST THAT SOUTHWEST FLOW AHEAD OF THE FRONT
WILL MAINTAIN ENOUGH MOISTURE FOR SOLID RAIN CHANCES ON SUNDAY.
HAVE THEREFORE INDICATED POPS IN THE 40 PERCENT RANGE SUNDAY
AFTERNOON AND EVENING. SUBSEQUENT SHIFTS WILL LIKELY BE ABLE TO
RAISE POPS FURTHER IF MODELS MAINTAIN CONSISTENCY. HIGH
TEMPERATURES ON SUNDAY WILL BE RELATIVELY MILD IN COMPARISON TO
PREVIOUS DAYS...RANGING FROM THE LOWER 50S INLAND TO AROUND 60
DEGREES SOUTHEAST GEORGIA. THE COLD FRONT WILL QUICKLY PROGRESS
OFFSHORE LATE SUNDAY NIGHT INTO MONDAY MORNING...WITH RAIN CHANCES
ENDING FROM WEST TO EAST.
COLD ADVECTION BEHIND THE FRONT WILL SUPPRESS HIGH TEMPERATURES ON
MONDAY IN THE UPPER 40S TO AROUND 50 DEGREES. DEEP UPPER LEVEL
TROUGH WILL REMAIN IN CONTROL OF THE EAST COAST THROUGH
TUESDAY...WHILE A SERIES OF EMBEDDED SHORTWAVES PASS OVER THE
FORECAST AREA. THE COLD AIR MASS WILL THUS LINGER ACROSS THE
SOUTHEAST STATES EARLY IN THE WEEK...AND BELOW NORMAL TEMPERATURES
CAN AGAIN BE EXPECTED ON TUESDAY WITH HIGHS IN THE UPPER 40S TO
LOWER 50S. WILL NEED TO CAREFULLY MONITOR MODEL TRENDS INDICATING
ANY LIGHT PRECIP ASSOCIATED WITH THE UPPER LEVEL ENERGY AND
LINGERING DEEP MOISTURE...ESPECIALLY MONDAY EVENING AS
TEMPERATURES DROP BELOW FREEZING. CONFIDENCE IS TOO LOW AT THIS
POINT TO INCLUDE MENTIONABLE RAIN CHANCES...BUT WILL NEED TO
MONITOR MODEL TRENDS TOWARD ANY WETTER SOLUTIONS.
ONCE THE AXIS OF THE UPPER LEVEL TROUGH SHIFTS OFF THE EAST COAST
BY WEDNESDAY...DRY SURFACE HIGH PRESSURE WILL BEGIN TO BUILD IN
FROM THE WEST. EXPECT A GRADUAL WARMING TREND...WITH HIGH
TEMPERATURES REACHING THE MID TO UPPER 50S BY THURSDAY. RAIN FREE
CONDITIONS WILL CONTINUE THROUGH MID WEEK. ANOTHER COLD FRONT
COULD APPROACH THE REGION FRIDAY.
&&
.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
VFR CONDITIONS WILL PREVAIL FOR THE NEXT 24 HOUR PERIOD AT BOTH KCHS
AND KSAV. EXPECT NORTHEASTERLY WINDS TO VEER TO THE SOUTH BY
SATURDAY EVENING...WITH SOUTHWESTERLY WINDS PREVAILING AT BOTH
TERMINALS ON SUNDAY. VFR CLOUD COVERAGE WILL INCREASE OVERNIGHT AS
ISENTROPIC LIFT ASSOCIATED WITH A DEVELOPING LOW APPROACHES FROM
THE WEST. SOME LLWS IS POSSIBLE AROUND SUNRISE SUNDAY MORNING AS
SOUNDINGS SHOWING 25 TO 30 KNOT WINDS AROUND 2000 FT...ESPECIALLY
FOR KCHS. YET WITH WINDS REMAINING SOUTHWESTERLY AT THIS
LEVEL...HAVE EXCLUDED THIS FROM EITHER TAF AS LLWS IS EXPECTED TO
REMAIN MARGINAL.
EXTENDED AVIATION OUTLOOK...POSSIBLE MVFR WEATHER WITH SHOWERS
LATE SUNDAY/EARLY SUNDAY NIGHT...OTHERWISE VFR CONDITIONS WILL
PREVAIL THROUGH THE PERIOD.
&&
.MARINE...
ONE FINAL SURGE OF N-NE WINDS HAS OCCURRED THIS MORNING WITH
LINGERING COLD AIR ADVECTION AND MODEST PINCHING. HOWEVER...WITH
THE END OF THE COLD AIR ADVECTION THIS AFTERNOON AND A RELAXATION
OF THE PRES GRADIENT AS HIGH PRES OVER THE MID ATLC AND DELMARVA
REGION EXTENDS SW ACROSS THE LOCAL AREA. THIS WILL RESULT IN NOT
ONLY A DECREASE IN WINDS...BUT ALSO ALLOW FOR VEERING TO THE E AND
SE BY DAYS END. SEAS WILL REMAIN HIGHER A LITTLE LONGER GIVEN THE
STRONGER WINDS THIS MORNING...BUT WILL FALL ABOUT A FOOT THIS
AFTERNOON WITH THE DECREASE IN WIND SPEEDS.
WINDS WILL BECOME SOUTHWESTERLY TONIGHT AS THE HIGH SHIFTS
FARTHER TO THE SOUTH. A DECENT LOW-LEVEL JET WILL SUPPORT SLIGHTLY
ENHANCED WINDS TONIGHT...MAINLY ACROSS THE GEORGIA OFFSHORE WATERS
AND THE SOUTH CAROLINA NEARSHORE WATERS. DO NOT BELIEVE WINDS WILL
GO ANY HIGHER THAN 15-20 KNOTS ATTM.
SUNDAY THROUGH WEDNESDAY...SOUTHWEST WINDS WILL INCREASE SUNDAY
AFTERNOON AHEAD OF A COLD FRONT APPROACHING FROM THE WEST...WITH
SMALL CRAFT ADVISORY CONDITIONS FOR WINDS AND SEAS POSSIBLE ACROSS
AT LEAST THE NORTHERN SOUTH CAROLINA WATERS AND THE OFFSHORE
GEORGIA MARINE ZONES. WINDS WILL BECOME WEST FOLLOWING FRONTAL
PASSAGE ON MONDAY...REMAINING ELEVATED DUE TO ENHANCED MIXING
WITHIN COLD ADVECTION. THE LINGERING COLD AIR MASS AND A
RELATIVELY TIGHT PRESSURE GRADIENT OVER THE WATERS WILL MAINTAIN
MODERATE OFFSHORE FLOW THROUGH AT LEAST TUESDAY...WITH ADVISORY
CONDITIONS POSSIBLY PERSISTING IN THE OFFSHORE GEORGIA WATERS.
WINDS WILL GRADUALLY DIMINISH MID WEEK AS HIGH PRESSURE BUILDS IN
FROM THE WEST.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...NONE.
SC...NONE.
MARINE...NONE.
&&
$$
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