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000 FXUS62 KTAE 171858 AFDTAE AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TALLAHASSEE FL 300 AM EDT FRI OCT 17 2008 .SYNOPSIS... 19Z WATER VAPOR AND H4 RUC ANALYSIS SHOWING AN AMPLIFYING UPPER LEVEL PATTERN THIS AFTERNOON ACROSS THE CONUS. FROM WEST TO EAST WE STILL FIND LONGWAVE RIDGING COVERING MUCH OF THE WESTERN U.S. AND SOUTHWEST CANADA. NORTHERN STREAM FLOW THEN DIPS INTO AN AMPLIFYING LONGWAVE TROUGH ACROSS THE MID-SECTION OF THE COUNTRY...WITH THE TROUGH AXIS NOW APPROACHING THE MS RIVER VALLEY. THE OVERALL FLOW THEN FLATTENS OUT AS IT EXITS THE EASTERN SEABOARD INTO THE WESTERN ATLANTIC. CURRENTLY OVERHEAD THE FORECAST AREA WE FIND THE UPPER LEVEL RIDGING THAT HAS BROUGHT THE FAIR AND WARM WEATHER TO THE AREA THE PAST SEVERAL DAYS BEGINNING SETTLING SOUTHWARD IN RESPONSE TO THE APPROACHING HEIGHT FALLS TO THE NORTHWEST. AT THE SURFACE...WEAK HIGH PRESSURE IN THE VICINITY IS SHIFTING SOUTH AS A COLD FRONT APPROACHES FROM THE NORTH. COLD FRONT IS CURRENTLY LOCATED FROM THE SOUTH CAROLINA COAST BACK THROUGH CENTRAL GA AND THEN SOUTHWEST IN SOUTHERN AL/MS. CLOUD-SHIELD IS QUITE THICK ALONG THIS BOUNDARY WITH A LARGE AREA OF SHOWERS FROM NEAR ATLANTA TO MONTGOMERY. THIS SHOWERS AND THICKER CLOUDS WILL CONTINUE TO DROP SOUTHWARD TOWARD OUR NORTHWESTERN ZONES INTO THE EVENING HOURS. && .SHORT TERM (TONIGHT THROUGH SUNDAY NIGHT)... SLOW MOVING COLD FRONT LOCATED TO OUR NORTH AND NORTHWEST WILL INCREASE ITS FORWARD PROGRESS SOUTHWARD AS MID-LEVEL TROUGHING/ENERGY OVER THE MID-SECTION OF THE COUNTRY AMPLIFIES INTO THE LOWER MS VALLEY AND SOUTHEASTERN STATES TONIGHT. FRONT PUSHES SOUTHEAST ACROSS THE FORECAST AREA TONIGHT REACHING A POSITION FROM AROUND VALDOSTA TO PERRY AND OUT INTO THE EASTERN MARINE LEGS BY SUNRISE SATURDAY MORNING. FRONT IS SOMEWHAT MOISTURE STARVED AS ANY INFLUX OF GULF MOISTURE HAS BEEN BRIEF. HOWEVER...AS THE SHORTWAVE AMPLIFIES INTO THE SOUTHEAST DURING THE OVERNIGHT... LARGE SCALE LIFT ASSOCIATED WITH THE RESPECTABLE HEIGHT FALLS SHOULD BE ENOUGH TO SUPPORT A BROKEN BAND OF SHOWERS ALONG AND AHEAD OF THE FRONTAL PASSAGE. DEEP LAYER Q-G FORCING AHEAD OF THE SHORTWAVE WITH THESE MID-LEVEL HEIGHT FALLS IS MAXIMIZED ACROSS OUR NORTHERN ZONES AND FURTHER NORTH. THEREFORE THE INHERITED FORECAST PHILOSOPHY WILL NOT CHANGE WITH HIGHEST POPS ACROSS OUR SE ALABAMA AND NORTHERN GA ZONES. SHOWERS SHOULD ARRIVE THIS EVENING INTO THE EARLY MORNING HOURS ACROSS OUR NORTHERN AND WESTERN ZONES AND THEN CONTINUE FURTHER SOUTHEAST AFTER MIDNIGHT. INSTABILITY CONTINUES TO BE ONLY MARGINAL AT BEST WITH LATEST SREF PROBS STILL SHOWING 0% FOR EVEN 500 J/KG OVER THE LAND. HOWEVER...CAN NOT RULE OUT AN ISOLATED THUNDERSTORMS...ESPECIALLY ALONG THE EASTERN PANHANDLE COAST...BUT MOST ACTIVITY SHOULD BE IN THE FORM OF SHOWERS. IT SHOULD BE NOTED THAT EVEN WITH THE LIKELY POPS ACROSS THE FAR NORTH...NOT LOOKING FOR A WASHOUT OF A NIGHT IN ANY LOCATION AS THE SHOWERS THAT DO OCCUR SHOULD BE BRIEF IN NATURE AND AMOUNT GENERALLY NO MORE THAN ONE OR TWO TENTH OF AN INCH OF ACCUMULATION AT BEST. GFS/NAM/ECMWF ALL SHOW THE COLD FRONT EXITING RAPIDLY TO THE SOUTHEAST OUT OF THE FORECAST AREA DURING THE FIRST HALF OF SATURDAY MORNING. GLOBAL MODELS SHOWING A VERY QUICK DRYING THROUGH THE COLUMN AS THE MID-LEVEL SHORTWAVE AXIS PASSES THE AREA. THEREFORE LOOKING FOR A RAIN FREE DAY REGIONWIDE AFTER A POSSIBLE QUICK EARLY MORNING SHOWER/SPRINKLE DOWN TOWARD PERRY OR CROSS CITY. THEREFORE MORNING CLOUDS ALONG THE FRONT OVER THE SOUTHEAST HALF OF THE AREA WILL BEGIN TO CLEAR WITH SKIES BECOMING PARTLY TO MOSTLY SUNNY BY AFTERNOON. A COOLER AND DRIER AIRMASS WILL ARRIVE DURING SATURDAY BEHIND THE FRONT WITH 850MB TEMPS DROPPING TO BETWEEN 7 AND 11C FROM NORTH TO SOUTH. THE COOLER AND DRIER AIR COMBINED WITH A 10-15 MPH NORTHERLY FLOW WILL PROVIDE A MORE FALL-LIKE FEEL TO YOUR SATURDAY AFTERNOON THAN WHAT HAS BEEN EXPERIENCED AS OF LATE. HIGH TEMPERATURES STRUGGLING TO REACH" onClick="return popup(this, 'notes')">REACH THE LOWER 80S SOUTHEAST AND THE UPPER 70S TO NEAR 80 ELSEWHERE. MID-LEVEL SHORTWAVE ENERGY EXITS OFF THE SOUTHEAST COAST SATURDAY NIGHT WITH MID-LEVEL RIDGING REBUILDING ALONG THE GULF COAST THROUGH THE REMAINDER OF THE SHORT-TERM PERIOD. STRONG 1025-1030MB SURFACE RIDGE ACROSS THE OHIO/MIDDLE MS VALLEYS WILL ALSO BUILD SOUTH AND EAST THROUGH THE PERIOD TO A POSITION FROM THE EASTERN SEABOARD TO THE NORTHEAST GULF OF MEXICO. THE RESULT WILL BE FAIR AND SEASONABLE WEATHER WITH TEMPERATURES GENERALLY A FEW DEGREES BELOW NORMAL. LOW TEMPERATURE FORECASTS ARE GOING TO BE ON THE DIFFICULT SIDE BOTH SATURDAY AND SUNDAY NIGHTS. AIRMASS IS ON THE COOL AND DRY SIDE...HOWEVER A FAIRLY TIGHT GRADIENT ON SATURDAY NIGHT SHOULD KEEP RADIATIONAL COOLING FROM REALLY TAKING HOLD AND DROPPING TEMPS TO LOW. MODELS STILL SHOW A FAIRLY TIGHT GRADIENT SUNDAY NIGHT...HOWEVER ON THESE SECOND NIGHTS BEHIND FRONTAL PASSAGE HAVE SEEN THE BOUNDARY LAYER ABLE TO DECOUPLE LATE DESPITE THE GRADIENT AND RESULT IN A RAPID TEMP DROP AROUND SUNRISE. TOO EARLY TO SAY IF THIS WILL OCCUR...BUT FEEL MORE CONFIDENT GOING WITH UPPER 40S INTO EARLY MONDAY MORNING. && .LONG TERM...(MONDAY 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... COLD FRONT WILL CROSS THE WESTERN MAINER LEGS TONIGHT AND THEN THE EASTERN LEGS EARLY SATURDAY. WINDS ARE EXPECTED TO INCREASE TO NEAR CAUTIONARY LEVEL ACROSS THE WESTERN LEGS FROM THE NORTH AND NORTHWEST TONIGHT. STRONG HIGH PRESSURE THEN SLOWLY BUILDS OVER THE WATERS THE REMAINDER OF THE UPCOMING WEEKEND INTO EARLY NEXT WEEK. EXPECTING NORTHERLY WINDS NEAR CAUTIONARY LEVELS OVER A LARGE PORTION OF THE AREA DURING THE DAYLIGHT HOURS ON SATURDAY WITH WINDS AND SEAS INCREASING TO NEAR ADVISORY LEVELS SATURDAY NIGHT INTO EARLY SUNDAY. THE EASTERLY FLOW AROUND THE SOUTHERN PERIPHERY OF THE HIGH TO OUR NORTH WILL FAVOR NOCTURNAL SURGES OF WINDS BOTH SUNDAY AND AGAIN MONDAY NIGHTS. && .AVIATION... A LARGE AREA OF LIGHT TO MODERATE RAIN OUT AHEAD OF THE COLD FRONT CONTINUES TO MOVE NE JUST TO THE NW OF THE CWA EARLY THIS AFTERNOON...WITH THE MAIN FCST CONCERN BEING IF/WHEN WILL SOME OF THIS RAINFALL AND POTENTIALLY LOW CIGS MAKE IT TO THE TAF SITES THIS EVENING AND TONIGHT. THE BEST PROBABILITIES FOR RAIN...LOW CIGS... AND EARLY ONSET OF PRECIPITATION WILL BE AT DHN AND ABY...WITH A TIME FRAME IN THE 02-07 UTC RANGE...WITH GRADUALLY LOWERING CHANCES AT PFN BETWEEN 04-08 UTC...TLH 06-10 UTC...AND VLD FROM 08-12 UTC. DHN COULD EVEN SEE A SHOWER OR SOME LIGHT RAIN BEFORE SUNSET...SO WILL CONTINUE TO MONITOR THE FRONTAL PROGRESS. DURING SAT MORNING... THE STRONG SHORTWAVE NOW DIGGING THROUGH THE MID MS VALLEY WILL BE CHARGING INTO THE CAROLINAS...AND THIS SHOULD HELP ACCELERATE THE COLD FRONT THROUGH THE CWA...WITH CLEARING SKIES AND GUSTY N-NW WINDS DEVELOPING FROM NW TO SE ACROSS THE TAF LOCATIONS. && .FIRE WEATHER... OUR RH GRIDS ARE NOT QUITE AS LOW AS THE PREVIOUS SHIFTS... WITH 35 PERCENT OR LESS NOW CONFINED TO INLAND WALTON... HOLMES...WASHINGTON...NORTHERN BAY...AND CALHOUN COUNTIES. WITH DISPERSIONS WELL ABOVE 75 IN THESE AREAS AS WELL...UPGRADED THE ABOVE ZONES TO A RED FLAG WARNING ON SAT AFTN...AND DROPPED THE WATCH FOR SE AL AND AREAS FURTHER EAST IN N FL. ON SUNDAY AFTERNOON ...ALMOST ALL OF N FL SHOULD HAVE SUB 35% RH COINCIDENT WITH >75 DISPERSIONS SO ISSUED A FIRE WX WATCH FOR ALL FL ZONES. && .PRELIMINARY POINT TEMPS/POPS... TALLAHASSEE 60 80 51 78 49 / 40 10 0 0 0 PANAMA CITY 62 81 54 78 54 / 40 10 0 0 0 DOTHAN 56 78 49 75 48 / 60 0 0 0 0 ALBANY 57 78 50 76 47 / 60 10 0 0 0 VALDOSTA 61 79 51 76 49 / 40 10 0 0 0 CROSS CITY 64 81 52 79 49 / 20 20 0 0 0 && .TAE WATCHES/WARNINGS/ADVISORIES... AL...NONE. GA...NONE. FL...FIRE WEATHER WATCH FROM SUNDAY AFTERNOON THROUGH SUNDAY EVENING FOR THE FOLLOWING ZONES: BAY...CALHOUN...DIXIE...FRANKLIN... GADSDEN...GULF...HOLMES...INLAND WALTON...JACKSON... JEFFERSON...LAFAYETTE...LEON...LIBERTY...MADISON...TAYLOR... WAKULLA...WASHINGTON. RED FLAG WARNING FROM 1 PM TO 5 PM CDT SATURDAY FOR THE FOLLOWING ZONES: BAY...CALHOUN...HOLMES...INLAND WALTON... JACKSON...WASHINGTON. GM...NONE. && $$ AVIATION/FIRE WEATHER...GOULD SYNOPSIS/SHORT TERM/MARINE...MROCZKA LONG TERM...WOOL