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000 FXUS62 KTAE 170636 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 236 AM EDT FRI OCT 17 2008 .SYNOPSIS...03 UTC SURFACE ANALYSIS SHOWS A COLD FRONT ACROSS THE SOUTHEAST FROM NORTHWEST LOUISIANA INTO EASTERN TENNESSEE AND ACROSS SOUTHERN VIRGINIA. AN AREA OF HIGH PRESSURE WAS ANALYZED ACROSS MINNESOTA. CONSIDERABLY COOLER AND DRIER AIR WAS NOTED BEHIND THIS COLD FRONT. SATELLITE OR RADAR IMAGERY THIS EVENING DOES NOT INDICATE MUCH IN THE WAY OF SHOWER ACTIVITY ALONG THIS BOUNDARY IN THE SOUTHEAST. THE UPPER AIR PATTERN IS NOT VERY AMPLIFIED AT THIS TIME WITH A TROF MOVING ACROSS THE WESTERN HIGH PLAINS. THIS TROF IS PROGGED TO DEEPEN AS IT NEARS THE EASTERN SEABOARD AND PUSH THIS COLD FRONT THROUGH OUR REGION BY SATURDAY MORNING. THE LARGE DEEP LAYER RIDGE REMAINS PARKED OVER THE NORTHERN GULF OF MEXICO. && .SHORT TERM...(TODAY THROUGH SUNDAY). FORECAST FOR THE SHORT TERM PERIOD IS FOCUSED PRIMARILY ON THE PROGRESSION OF THE COLD FRONT THROUGH THE SOUTHEAST. OVER THE LAST SEVERAL RUNS THE GENERAL TREND HAS BEEN FOR THE FRONT TO CLEAR MUCH OF OUR CWA BY 12Z SATURDAY. THE OVERRIDING TREND IN THE GFS HAS BEEN FOR STRONGER FORCING...THUS MORE QPF. THE NAM IS A LITTLE WEAKER WITH THE FORCING ON THE SOUTHERN EXTENT OF THE FRONTAL SYSTEM...AND ALSO STRINGS OUT THE MOISTURE A LITTLE BIT. VAPOR IMAGERY EARLY THIS MORNING SHOWS THE TROF OVER THE UPPER PLAINS BEGINNING TO DEEPEN AS IT APPROACHES THE MISSISSIPPI RIVER VALLEY. WITH THE TROF AMPLIFYING WHILE MOVING EASTWARD...ASSOCIATED Q-G FORCING WILL INCREASE WITH TIME AND BE STRONGEST NEARER THE GREATEST HEIGHT FALLS OVER NORTHEAST TENNESSEE AND WESTERN NORTH CAROLINA. THE TREND IN THE MOS HAS BEEN FOR HIGHER POPS FOR TODAY AND TONIGHT. THIS SEEMS TO MAKE SENSE GIVEN THE DEEP LAYER MOISTURE AND FORCING ACCOMPANYING THE FRONT. WITH THE FRONT STILL LOCATED ACROSS THE MID SOUTH...WILL KEEP POPS RELATIVELY LOW IN THE NORTHWESTERN ZONES AS IT WILL TAKE SOME TIME FOR THE FRONT TO KICK IT INTO GEAR AND MOVE EASTWARD AS THE TROF FINALLY CATCHES UP THIS AFTERNOON. WILL THEREFORE KEEP ALL POPS LESS THAN 10 PERCENT PRIOR TO 18Z TODAY. AFTER 18Z...WILL SHOW AN INCREASING TREND WITH POPS...BUT SHOULD REMAIN ALL DRY EAST OF A LINE FROM FITZGERALD TO PANAMA CITY. WILL BE QUITE WARM AGAIN IN THE EASTERN CWA WHERE CLOUD COVER WILL ARRIVE LATE IN THE DAY. TEMPERATURES WILL ONCE AGAIN APPROACH 90 IN THE SUWANNEE RIVER VALLEY...BUT WE SHOULD REMAIN BELOW ANY RECORDS FOR THE DATE (THE DAILY MAX RECORD FOR TLH IS 90). TONIGHT...WITH A RAPIDLY DEEPENING TROF...THE COLD FRONT IS EXPECTED TO MOVE THROUGH THE REGION OVERNIGHT AND APPROACH OUR SOUTHEASTERN CWA BORDER BY 12Z. A LINE OF SHOWERS SHOULD PRECEDE THIS FRONT. WITH FORCING GREATEST IN THE EVENING AND EARLY MORNING HOURS IN OUR NORTHERN ZONES...THINK IT IS APPROPRIATE AT THIS TIME TO INCREASE POPS TO THE LIKELY CATEGORY. THE NEW NAM MOS SEEMS A LITTLE TOO HIGH FOR MY TASTE AT THIS POINT WITH POPS NEAR 80 PERCENT AT ALBANY. GENERALLY USED A BLEND OF THE NEW NAMMOS/MAVMOS AND SREF TO ARRIVE AT THE POP GRID FOR THIS PERIOD. GIVEN THE FORCING AVAILABLE...CONSIDERED KEEPING THE ISOLATED THUNDER IN THE FORECAST...BUT LAPSE RATES APPROACH 6 DEG C/KM WITH THE FRONT...PRODUCING NEGLIGIBLE CAPE (25 J/KG OR LESS)...SO WILL REMOVE THE THUNDER FROM THE FORECAST OVER THE LANDMASS. SATURDAY...THE COLD FRONT SHOULD CLEAR CROSS CITY BY 15Z WITH MUCH DRIER AND COOLER AIR FILTERING INTO THE CWA THROUGHOUT THE DAY. MAX TEMPERATURES WILL DROP BACK INTO THE UPPER 70S TO LOW 80S...BUT THE COOLER DAY WILL BE ON SUNDAY. SATURDAY NIGHT...SURFACE PRESSURE GRADIENT REMAINS TIGHT AS A SURFACE HIGH SLIDES DOWN THE EASTERN SEABOARD. THIS WILL KEEP SURFACE WINDS ABOVE 5 MPH THROUGHOUT MUCH OF THE NIGHT AND WILL PREVENT TEMPERATURES FROM PLUMMETING TOO FAR. LATEST GUIDANCE HAS BEEN WAFFLING BETWEEN LOW 50S AND UPPER 40S. THIS RUN IS LARGELY IN THE UPPER 40S ALL INLAND SITES. GIVEN THE WIND...WOULD PREFER TO GO TOWARD A WARMER SOLUTION OF THE LOW 50S...EXCEPT FAR NORTHWESTERN ZONES WHERE THERE IS THE POTENTIAL SHELTERED LOCATIONS MAY GO CALM TOWARD DAYBREAK. SUNDAY...BREEZY NORTHEAST WINDS WILL HELP SUNDAY FEEL LIKE A TRUE FALL DAY WITH TEMPERATURES ONLY MAKING IT INTO THE MID 70S AREA WIDE UNDER FULL SUNSHINE. .LONG TERM...(SUNDAY NIGHT THROUGH FRIDAY). HIGH PRESSURE WILL BE IN CONTROL OF THE WEATHER AT THE START OF THE PERIOD WITH A SURFACE RIDGE EXTENDING FROM THE NE/MID ATLANTIC SWWD ACROSS THE DEEP S. THIS WILL PROVIDE THE AREA WITH ANOTHER COOL DAY ON MON, WITH MINS SIMILAR TO SUN...SEVERAL DEGREES BELOW NORMAL... AND MAX TEMPS JUST A FEW DEGREES WARMER. UPPER LEVEL RIDGING WILL THEN MOVE EWD FROM THE SRN PLAINS WITH BOTH MAX AND MIN TEMPS MODERATING TO SLIGHTLY ABOVE NORMAL BY TUE-WED. BY MID WEEK...WE BEGIN TO SEE SOME SIGNIFICANT DIFFERENCES DEVELOP IN THE MODEL SOLUTIONS. BOTH THE GFS AND 16/12Z EURO OPERATIONAL RUNS DEEPEN A TROUGH OVER CENTRAL N AMERICA. HOWEVER...THE GFS DROPS THE OCCLUDED SYSTEM MUCH FURTHER S AND W THAN THE EURO...INTO THE CENTRAL PLAINS...WHERE IT SITS AND SPINS FOR DAYS. THE EURO BRINGS THE STACKED LOW INTO THE UPPER MS VALLEY AND THEN SWINGS IT EWD ACROSS THE LAKES INTO THE WEEKEND. THESE DIFFERENCES IMPACT DEVELOPMENTS IN THE TROPICS AS WELL, WHERE BOTH MODELS SHOW LOW PRESSURE DEVELOPING IN THE NWRN CARIBBEAN SEA. THE EURO`S TROUGH IS FAR ENOUGH N THAT IT DOES NOT PICK UP THIS FEATURE WHICH SPINS IN PLACE THROUGH MOST OF NEXT WEEK. THE GFS PICKS UP THE LOW AND LIFTS IT SLOWLY NWD THROUGH THE YUCATAN CHANNEL INTO THE SERN GULF OF MEXICO FROM WED-FRI. WITH THE FRONT STALLED UPSTREAM AND MOISTURE INCREASING FROM THE S AND E...THE GFS PRESENTS A MUCH CLOUDIER AND BREEZIER SCENARIO FOR LATE IN THE WEEK THAN THE EURO...WHICH SHOWS A CLEAN COLD FROPA ON FRI. THE GFS ENSEMBLE MEAN IS MUCH CLOSER TO THE EURO SOLUTION WITH RESPECT OT THE POSITION OF THE 500 MB HIGH ON FRI. CONSIDERING THE SPREAD OF THE ENSEMBLE MEMBERS THROUGH, WE ARE NOT CONFIDENT ENOUGH TO GO STRICTLY WITH THE EURO. WE WILL GENERALLY FOLLOW THE GFS/MEX FOR POP...BUT WILL SCALE BACK THE AMOUNT OF CLOUD COVER AND ELY WINDS IN THIS MODEL. IN OTHER WORDS...WE WILL BE HOLDING OFF ON ANY INDICATION OF A TROPICAL ENTITY IN THE GULF UNTIL WE SEE A TREND TOWARD THIS SOLUTION WHICH...BY THE WAY...DOES FIT THE CLIMATOLOGY FOR LATE OCT IN THE ATLANTIC BASIN. && .MARINE...WINDS AND SEAS WILL REMAIN LOW TODAY WITH WEAK HIGH PRESSURE OVER THE WATERS. THIS HIGH WILL MOVE EAST AND THE PRESSURE GRADIENT WILL TIGHTEN AS THE COLD FRONT APPROACHES TONIGHT. EXPECT WINDS TO PICK UP AND SEAS TO BUILD AS THE COLD FRONT MOVES INTO THE WESTERN WATERS AFTER MIDNIGHT ON SATURDAY AND REMAIN ELEVATED THROUGHOUT THE REMAINDER OF THE WEEKEND. WITH THE SURFACE RIDGE BUILDING DOWN THE EASTERN SEABOARD ON SATURDAY NIGHT...PERIODS OF ADVISORY CONDITIONS WILL BE POSSIBLE SATURDAY AND SUNDAY NIGHTS WITH WINDS IN THE 20 TO 25 KNOT RANGE AND SEAS BUILDING TO 6 TO 8 FEET WELL OFFSHORE. SATURDAY/SUNDAY AFTERNOONS SHOULD FEATURE CAUTIONARY CONDITIONS IN THE WAKE OF THE COLD FRONT. THE RIDGE SHOULD BUILD FAR ENOUGH SOUTH TO ALLOW WINDS AND SEAS TO DIMINISH BELOW HEADLINE CRITERIA BY TUESDAY AFTERNOON. && .AVIATION...THIS TAF SET REPRESENTS A CONTINUATION OF OUR THINKING ON THE TIMING OF THE NEXT FRONT AND A LESS PESSIMISTIC OUTLOOK" onClick="return popup(this, 'notes')">OUTLOOK FOR THIS MORNING CONCERNING DEVELOPMENT OF LIFR CONDITIONS. CONDENSATION PRESSURE DEFICIT CHARTS AND SREF PROBABILITIES ALL INDICATE A MUCH LOWER CHANCE FOR FOG DEVELOPMENT OVER ERN AREAS (VLD) THAN OCCURRED THU MORNING...AND THIS IS REFLECTED IN THE MOS. WE THEREFORE PULLED WAY BACK IN THE VLD TERMINAL AND ARE NOW ONLY CALLING FOR MVFR VSBY THERE. SIMILAR CONDITIONS ARE EXPECTED AT THE OTHER TERMINALS...WITH THE GREATEST CONFIDENCE FOR MVFR VSBY SHIFTING TO AREAS W OF TLH FOR THIS MORNING (PFN AND DHN). WE INCLUDED PROB30 GROUPS FOR AFTERNOON SHOWERS AND VFR CEILINGS OF 4-5 KFT AT DHN AND ABY...WITH TEMPOS FOR THE EVENING HOURS WHEN FROPA OCCURS. FURTHER SE...LOOK FOR RAIN CHANCES TO HOLD OFF UNTIL AFTER 00Z. && .FIRE WEATHER...WE ARE LOOKING FOR 2-3 HOUR DURATIONS OF RH AOB 35 PERCENT THIS AFTERNOON OVER ERN PORTIONS OF THE FL BIG BEND AND THIS WILL BE MENTIONED IN THE DISCUSSION/REMARKS WITH NO WARNING NECESSARY. DRIER AIR WILL QUICKLY RETURN TO THE AREA BEHIND THE FRONT SAT AFTERNOON. IT APPEARS THAT DURATIONS WILL BE SUFFICIENT FOR A WATCH TO BE POSTED FOR OUR FL ZONES FROM JEFFERSON COUNTY WWD. SE AL WILL BE A CLOSE CALL FOR SAT. MON RH WILL BE DOWN AROUND 30 WITH 20-FT WINDS OVER 10 MPH. THE KBDI IS CURRENTLY ABOVE 500. IT IS HARD TO TELL HOW FAR IT WILL DROP AFTER THE RAIN LATER TODAY AND TONIGHT...SO BECAUSE OF THAT UNCERTAINTY...WE WILL POST A WATCH FOR THOSE 5 COUNTIES AS WELL. && .PRELIMINARY POINT TEMPS/POPS... TALLAHASSEE 86 60 80 51 75 / 5 40 5 0 0 PANAMA CITY 83 63 78 58 77 / 10 50 0 0 0 DOTHAN 81 56 78 50 76 / 40 60 0 0 0 ALBANY 84 58 78 50 75 / 20 60 0 0 0 VALDOSTA 87 60 78 50 75 / 5 40 10 0 0 CROSS CITY 88 63 81 53 78 / 0 20 20 0 0 && .TAE WATCHES/WARNINGS/ADVISORIES... AL...FIRE WEATHER WATCH SATURDAY AFTERNOON FOR THE FOLLOWING ZONES: COFFEE...DALE...GENEVA...HENRY...HOUSTON. GA...NONE. FL...FIRE WEATHER WATCH SATURDAY AFTERNOON FOR THE FOLLOWING ZONES: BAY...CALHOUN...FRANKLIN...GADSDEN...GULF...HOLMES...INLAND WALTON...JACKSON...JEFFERSON...LEON...LIBERTY...WAKULLA... WASHINGTON. GM...NONE. && $$ AVIATION/LONG TERM/FIRE WEATHER...WOOL REST OF DISCUSSION...GODSEY