000 FXUS62 KKEY 242123 AFDKEY AREA FORECAST DISCUSSION FOR THE FLORIDA KEYS NATIONAL WEATHER SERVICE KEY WEST FL 425 PM EST TUE NOV 24 2009 .DISCUSSION...IN THE MIDDLE AND UPPER LEVELS...700-200 MB...LATEST WATER VAPOR AVAILABLE SATELLITE IMAGERY OVERLAID WITH STREAMLINE ANALYSIS AS OF 2 PM DEPICT THE MAIN AXIS OF NORTH TO SOUTH ORIENTED TROUGH LOCATED FROM MINNESOTA TO OKLAHOMA. SOUTH OF THAT...THERE IS AN APPROX 75 TO 100 KNOT JET AT 250 MB CONTINUING ACROSS MEXICO...THE GULF OF MEXICO...TO FLORIDA AND THE KEYS. OF MOST SIGNIFICANCE WITHIN THIS SOUTHERN JETSTREAM...IS A DEVELOPING MID AND UPPER MESOSCALE DISTURBANCE AS INDICATED BY A LARGE AREA OF SHOWERS AND THUNDERSTORMS ENCOMPASSING MUCH OF THE WESTERN GULF. THE FLORIDA KEYS ARE UNDERNEATH THIS STRONG JET AND DOWNSTREAM OF THIS SYSTEM. IN THE LOWER TO MIDDLE LEVELS...SURFACE TO 700 MB...LATEST IR SATELLITE IMAGERY OVERLAID WITH AVAILABLE SURFACE AND MARINE OBSERVATIONS AS OF 200 PM DETAIL A 1006 MB LOW NEAR IOWA WHICH TRAILS A COLD FRONT TO SOUTHEAST TEXAS. A TROUGH OF LOW PRESSURE CURRENTLY EXTENDS SOUTHWEST TO ACROSS THE FLORIDA PENINSULA AND WESTWARD INTO BROAD LOW PRESSURE IN THE WESTERN GULF OF MEXICO FROM LOW PRESSURE OFF THE VIRGINIA CAPES. AS A RESULT...THERE IS A MOISTENING EAST TO SOUTHEAST FLOW FROM THE SURFACE TO 700 MB. .CURRENTLY...AS OF 200 PM...SATELLITE IMAGERY DETECTS PARTLY TO MOSTLY CLOUDY SKIES ACROSS THE KEYS ISLAND CHAIN AND ADJOINING WATERS. TEMPERATURES HAVE REACHED INTO THE LOWER 80S WITH DEWPOINTS IN THE LOWER 70S. RADAR INDICATES ISOLATED SPRINKLES OR VERY LIGHT RAIN SHOWERS OVER THE FLORIDA STRAITS. C-MAN STATIONS ARE RECORDING EAST WINDS BETWEEN 10 AND 15 KNOTS AND NEAR 10 KNOTS IN SOUTHERN FLORIDA BAY. .SHORT TERM (REST OF TODAY)...IN THE MIDDLE AND UPPER LEVELS...(700-200 MB)...TONIGHT THROUGH FRIDAY...LARGE SCALE MODELS CONTINUE TO INDICATE THAT THE LONG WAVE PATTERN AND ASSOCIATED PATTERN WILL ALLOW FOR SIGNIFICANT AMPLIFICATION OF THE MAIN TROUGH TONIGHT THROUGH FRIDAY. THE MID AND UPPER DISTURBANCE OVER THE WESTERN GULF OF MEXICO WILL DRAW AMPLE MOISTURE AND LIFT OUT AHEAD OF IT TO OVER THE KEYS. THE 12Z GFS AND NAM FORECAST SOUNDINGS INDICATE PWAT(PRECIPITABLE WATER) AROUND 2 INCHES AS WELL AS CROSS SECTION HINTING AT WEAK LOW TO MIDDLE LEVEL OMEGA FIELDS PRESENT. THOUGH MOST OF THE DYNAMICS WILL BE NORTH OF THE KEYS ATTM...WILL KEEP THUNDER IN THE FORECAST PERIOD. SO RAIN CHANCES WILL BE WELL ABOVE NORMAL THROUGH THURSDAY NIGHT...WHEN PWAT FALLS TO BETWEEN THREE QUARTERS AND ONE INCH ON BY 12Z FRIDAY MORNING. THEREAFTER VERY DRY MIDDLE AND UPPER AIR IS USHERED IN WITHIN THE DRY CYCLONIC FLOW WITHIN THE LARGE GYRE AS THE MAIN TROUGH AXIS PASSES FLORIDA COINCIDENT WHEN THE UPPER LOW REACHES THE OHIO VALLEY. EXTENDED...FRIDAY NIGHT THRU TUESDAY...LARGE SCALE MODELS INSISTENT THAT A RATHER PROGRESSIVE PATTERN WILL CONTINUE TO BE IN PLACE. A STRONG SOUTHERN JET WILL CONTINUE ACROSS THE GULF OF MEXICO...FLORIDA...AND THE KEYS...IN THE WAKE OF THE DEPARTING TROUGH. FOR THE UPCOMING WEEKEND. ANOTHER DEEP TROUGH WILL TAKE SHAPE SUNDAY NIGHT OVER THE MISSISSIPPI VALLEY WHICH WILL GRADUALLY AMPLIFY AGAIN ON MONDAY AND TUESDAY...WITH THE POSSIBILITY OF ONCE AGAIN ADVECTING LARGE AMOUNTS OF MOISTURE AND MID LEVEL LIFT TO OVER THE KEYS MONDAY AND TUESDAY. IN THE LOWER TO MID LEVELS...SURFACE TO 700 MB...TONIGHT THROUGH FRIDAY. BY ALL AVAILABLE MODEL INDICATIONS...A WELL ADVERTISED WET PATTERN WILL ENSUE OVERNIGHT AS WELL AS DURING THE DAY ON WEDNESDAY AND WEDNESDAY NIGHT...CONTINUING INTO THURSDAY. FOR TONIGHT THRU WEDNESDAY NIGHT...SCATTERED SHOWERS WILL DEVELOP LATER TONIGHT WITHIN INCREASING LOW AND MIDDLE ADVECTION OF MOISTURE. THIS IN COMBINATION WITH THE APPROACHING VORTICITY OVER THE GULF OF MEXICO...AND ACCOMPANIED BY THE MIDDLE LEVEL OMEGA. THOUGH MOST OF THE STRONGER DYNAMICS WILL BE NORTH OF THE KEYS...ISOLATED THUNDERSTORMS HAVE BEEN MAINTAINED IN THE FORECAST. TEMPERATURES TONIGHT WILL MOST LIKELY APPROACH THE DEWPOINT WITHIN HEAVY RAINSHOWERS AND ISOLATED THUNDERSTORMS...SO LOWS BETWEEN 70 AND 75 HAVE BEEN IN PLACE. ON WEDNESDAY...GIVEN DEEP MOISTURE AND AVAILABLE ENERGY PASSING BY TO THE NORTH...SHOWERS WILL BECOME MORE NUMEROUS. THOUGH THE KEYS WILL BE IN THE WARM SECTOR...GIVEN THE CANOPY OF CLOUDINESS AND LACK OF SOLAR INSOLATION...WILL HOLD HIGH TEMPERATURES ONLY IN THE LOWER 80S. THANKSGIVING DAY AND THURSDAY NIGHT...THE MODELS HAVE BEEN AMBIGUOUS WITH SURFACE LOWER PRESSURE DEVELOPMENT ALONG THE STATIONARY FRONT. 12Z GFS AND ECMWF DEVELOP A SURFACE LOW OFF OF THE FLORIDA COAST WEDNESDAY NIGHT AND INTENSIFY THE SYSTEM ON THURSDAY AND THURSDAY NIGHT AS IT MOVES NORTHEASTWARD. NEVERTHELESS...AS THE LOW DEVELOPS AND MOVES NORTHEASTWARD...IT WILL DRAG THE FRONT SOUTHWARD ACROSS THE PENINSULA AND APPROACH THE KEYS LATE IN THE DAY. HOWEVER...A LOWER LEVEL BAND OF MOISTURE ASSOCIATED WITH CLOUDINESS AND BRIEF LIGHT RAIN SHOWERS WILL PROBABLY BE AROUND DURING THURSDAY EVENING. IT LOOKS MOST LIKELY THAT THE ACTUAL FRONT WILL MOVE ACROSS THE KEYS ON THURSDAY NIGHT. FRIDAY AND SATURDAY...1025 MB RIDGE OVER THE SOUTHERN PLAINS FRIDAY MORNING WILL SLIDE QUICKLY EASTWARD TO NORTH FLORIDA BY SATURDAY NIGHT. BEHIND THE FRONT WILL USHER IN OUR NEXT FRONT OF THE YEAR. MUCH COOLER AND DRIER AIR WILL GRADUALLY MOVE INTO THE KEYS...BUT WINDS ARE EXPECTED TO VEER AROUND TO NORTHWEST TO NORTH THURSDAY NIGHT TO NORTHEAST BY SATURDAY. HI AND LOW TEMPERATURES WILL BE A FEW DEGREES BELOW NORMAL. SUNDAY NIGHT THROUGH TUESDAY...A RATHER RAPID VEERING AND MOISTENING OF THE BOUNDARY LAYER IS ON TAP AS MOISTENING IS EXPECTED AS WEAK RIDGING BUILDS NORTH OF THE KEYS SUNDAY AND SUNDAY NIGHT. TEMPERATURES RETURN TO NEAR NORMAL SUNDAY AND SUNDAY NIGHT WITH ISOLATED SHOWERS. MODELS HINT AT ANOTHER FRONTAL PASSAGE MONDAY AND TUESDAY. GIVEN THE DEARTH OF MOISTURE IN PLACE...ISOLATED SHOWERS HAVE ALREADY BEEN PUT IN THE FORECAST. && .MARINE...NO MARINE ISSUES UNTIL THURSDAY WHEN COLD FRONT MOVES RAPIDLY SOUTHWARD DOWN THE FLORIDA PENINSULA. SMALL CRAFT WILL LIKELY NEED TO EXERCISE CAUTION THURSDAY NIGHT AND FRIDAY WHEN WINDS BETWEEN 15 AND 20 KNOTS ARE EXPECTED. THERE IS THE POSSIBILITY THAT ADVISORIES MAY BE NECESSARY DEPENDING ON THE STRENGTH OF THE EAST COAST ARE OF LOWER PRESSURE. WINDS AND SEAS WILL GRADUALLY LET DOWN FOR THE WEEKEND...WITH ANOTHER COLD FRONT APPROACHING NEXT WEEK. && .AVIATION... VFR CONDITIONS WILL PREVAIL THROUGH EARLY THIS EVENING AT THE KEYS ISLAND TERMINALS THROUGH THIS EVENING. SCATTERED CLOUDS AROUND FL030 WITH BROKEN CLOUD DECKS ABOVE FL250. WINDS WILL CLOCK AROUND THE COMPASS ROSE FROM EAST NORTHEAST TO NEARLY SOUTH BY 15Z WEDNESDAY BLOWING AROUND 7 TO 9 KNOTS TONIGHT...INCREASING TO 8 TO 12 KNOTS AFTER SUNRISE. HAVE A VCSH IN THE TAF AFTER 03Z WITH POSSIBLE MVFR CEILINGS DUE TO LOWERING SCATTERED CLOUDS TO FL020 AND A BROKEN DECK AROUND FL070. && .CLIMATE... ON THIS DAY IN KEYS WEATHER HISTORY...IN 1957...THE TEMPERATURE RECORDED AT THE KEY WEST AIRPORT WAS 87 DEGREES. THIS IS THE RECORD HIGH TEMPERATURE FOR NOVEMBER 24TH...A RECORD WHICH REMAINS IN TACT TODAY...52 YEARS LATER. && .PRELIMINARY POINT TEMPS/POPS... KEY WEST 74 81 74 / 50 60 60 MARATHON 74 81 74 / 50 60 60 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...NONE. GM...NONE. && $$ PUBLIC/MARINE/GRIDS............FUTTERMAN AVIATION/NOWCASTS..............COTTRILL DATA ACQUISITION/UPPER AIR.....ROSS VISIT US ON THE WEB AT WWW.WEATHER.GOV/KEYWEST