428 
FXUS62 KTAE 210953
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
453 AM EST SAT NOV 21 2009

.SYNOPSIS...
THE 09 UTC REGIONAL SURFACE ANALYSIS AND IR SATELLITE IMAGERY SHOWED
A 1008 MB LOW OFF THE TX COAST AND AN AREA OF HIGH PRESSURE (AND
COOL DRY AIR) OVER MUCH OF THE SOUTHEAST. A COLD FRONT TRAILED THE
LOW TO THE SOUTH...WHILE A WARM FRONT EXTENDED SOUTHEASTWARD FROM
THE LOW. A SMALL BUT FAIRLY VIGOROUS MCS HAD DEVELOPED JUST EAST
OF THE SURFACE LOW...WHILE ISOLATED STORMS DEVELOPED ALONG THE
WARM FRONT AND IN THE WARM SECTOR. THESE STORMS HAD A SHEARED...SUPER
CELL APPEARANCE. VAPOR IMAGERY AND UPPER AIR DATA SHOWED A TROUGH
PROPAGATING EASTWARD ALONG THE TX COAST...WITH ABUNDANT HIGH LEVEL
CLOUDS STREAMING EASTWARD WELL AHEAD OF THE APPROACHING SYSTEM.

&&

.SHORT TERM...
(TODAY THROUGH MONDAY) THERE HAVE BEEN SOME CHANGES IN THE MODEL 
RUNS COMPARED TO 24 HOURS AGO...WITH A CONSENSUS SHIFTING TOWARD A 
WEAKER LOW WITH A MORE SOUTHERLY TRACK. IN FACT...THE MAJORITY OF 
NUMERICAL GUIDANCE ALL BUT DISSIPATES THE SURFACE LOW AS IT QUICKLY 
OCCLUDES NEAR OR OVER OUR FORECAST AREA SUNDAY NIGHT AND MONDAY. 
WHILE THERE WILL LIKELY BE SUFFICIENT DEEP LAYER MOISTURE AND 
SYNOPTIC SCALE ASCENT FOR A WIDESPREAD RAIN EVENT...THE PROBABILITY 
OF A SIGNIFICANT SEVERE WEATHER EVENT APPEARS TO BE DIMINISHING. THE 
LATEST GUIDANCE HAS ALSO TRENDED A BIT SLOWER THAN PREVIOUS 
RUNS...SO THAT THE BULK OF THE RAIN WILL LIKELY HOLD OFF UNTIL 
TONIGHT...AND LAST THROUGH SUNDAY MORNING. SOME OF THIS SLOW-DOWN 
MAY BE DUE TO THE EXTENSIVE DEPTH OF DRY AIR ENTRENCHED OVER OUR 
REGION...AS IT MAY TAKE AWHILE FOR THE PRECIPITATION ALOFT TO 
MOISTEN THE VERY DRY MID TROPOSPHERE. 

ALTHOUGH THE SEVERE STORM THREAT APPEARS SMALL AT THIS TIME...IT IS 
NOT NEGLIGIBLE. THE MOST FAVORABLE OVERLAP OF VERTICAL WIND 
SHEAR...DEEP LAYER MOISTURE...LIFT...AND INSTABILITY APPEARS TO BE 
BETWEEN 06 UTC TONIGHT AND 18 UTC SUNDAY. THE THREAT WILL BEGIN 
OFFSHORE THE FL PANHANDLE TONIGHT...THEN MOVE EAST ACROSS NORTH FL 
AND EXTREME SOUTH GA SUNDAY. THERE IS LITTLE DOUBT THAT THE LOCAL 
DEEP LAYER AND LOW LAYER VERTICAL WIND SHEAR PROFILES WILL BE MORE 
THAN SUFFICIENT TO SUPPORT ROTATING UPDRAFTS. THE QUESTION...AS 
USUAL THIS TIME OF YEAR...IS WHETHER OR NOT THERE WILL BE ENOUGH 
INSTABILITY TO SUPPORT SURFACE BASED SUPER CELLS. THE CONSENSUS OF 
GUIDANCE SUGGESTS THE BULK OF THE MARITIME TROPICAL AIRMASS WILL 
REMAIN JUST SOUTH OF THE COAST...LIMITING THE THREAT OF SEVERE 
STORMS OVER LAND. BY THE TIME THE INSTABILITY INCREASES OVER LAND 
SUNDAY AFTERNOON...THE BEST SHEAR AND LIFT WILL LIKELY HAVE WEAKENED 
AND/OR MOVED OFF TO OUR NORTHEAST. THE SPC FORECASTS A 2 PERCENT 
CHANCE OF A TORNADO WITHIN 25 MILES OF A POINT...AND A 5 PERCENT 
CHANCE OF DAMAGING STRAIGHT LINE WINDS. WE SUSPECT THERE WILL BE
ISOLATED SUPER CELLS NEAR AND SOUTH OF OUR COASTLINE...BUT THEN
THEY WILL BECOME ELEVATED AS THEY MOVE INLAND. IT IS IMPORTANT TO
REMEMBER THAT EVEN THE BEST MODELS RARELY RESOLVE SMALL SCALE
DETAILS (LIKE THE LEADING EDGE OF THE MARITIME TROPICAL AIR FROM
THE GULF) BEYOND 24 HOURS...SO IT REMAINS POSSIBLE THAT IF THE
COASTAL FRONT MOVES INLAND MORE THAN EXPECTED THERE WOULD BE AN
ENHANCED SEVERE STORM RISK.

.LONG TERM...
(MONDAY NIGHT THROUGH SATURDAY) SIGNIFICANT DIFFERENCES REMAIN
BETWEEN THE GFS AND THE ECMWF THROUGH THE MIDDLE OF THE WEEK WITH
RESPECT TO THE DEVELOPMENT OF ANOTHER LOW IN THE GULF OF
MEXICO...AND THE RESULTING POTENTIAL IMPACTS OF CLOUDS AND
POSSIBLE PRECIPITATION ACROSS THE TRI-STATE AREA. AS A
RESULT...OVERALL CONFIDENCE IN THAT PORTION OF THE FORECAST
REMAINS LOWER. HOWEVER THE LATEST ECMWF HAS TRENDED TOWARD A
SLIGHTLY MORE SOUTHERN DEVELOPMENT WHILE THE GFS HAS TRENDED
SLIGHTLY NORTHWARD. WILL GO WITH A BLEND AS BASIC GUIDANCE...AND
LEAN TOWARDS THE GFS SOLUTION FOR CONSISTENCY...HOLDING ON TO MORE
CLOUDS THROUGH WEDNESDAY NIGHT AND ADJUSTING TEMPERATURES
ACCORDINGLY. AS THE SECOND LOW MOVES EAST TOWARD THE END OF THE
WEEK...BOTH MODELS SHOW HIGH PRESSURE AND COOLER DRIER AIR
SPREADING EASTWARD ACROSS THE AREA THROUGH THE REMAINDER OF THE
FORECAST PERIOD. WILL SHOW TEMPERATURES STARTING OUT ABOVE
NORMAL...THEN TRENDING DOWNWARD TO NEAR NORMAL THROUGH THE MIDDLE
OF THE WEEK...AND BELOW NORMAL BY THE END OF THE WEEK.

&&

.AVIATION...
EXPECT PATCHES OF MVFR VISIBILITIES WITH FOG MAINLY ACROSS THE
FLORIDA BIG BEND AND SOUTH CENTRAL GEORGIA...AND AREAS OF LOW MVFR
TO IFR CEILINGS SPREADING WESTWARD INTO SOUTH CENTRAL GEORGIA BY
DAYBREAK...AS REFLECTED IN THE TAFS FOR KVLD AND KTLH. ELSEWHERE
VFR CONDITIONS WILL PREVAIL WITH ONLY CIRRUS. BY AFTERNOON A
DEVELOPING AREA OF LOW PRESSURE OVER THE WESTERN GULF OF MEXICO
WILL SPREAD THICKENING AND LOWERING CLOUDS EASTWARD ACROSS THE
AREA...WITH MVFR CEILINGS AND VISIBILITIES WITH SHOWERS DEVELOPING
ACROSS SOUTHEAST ALABAMA AND THE EASTERN FLORIDA PANHANDLE BY
LATER AFTERNOON...SPREADING EASTWARD ACROSS THE REMAINDER OF THE
AREA SATURDAY NIGHT.

&&

.MARINE...
WITH A WEAKER SYSTEM BEING FORECAST BY THE MODELS...IT APPEARS LESS 
LIKELY THAT AN ADVISORY WILL BE NEEDED LATER TONIGHT OR SUNDAY. THE 
00 UTC WAVEWATCH INDICATES LOWER SEAS THAN 24 HOURS AGO...BUT WE 
LOWERED ITS SEAS FORECAST A FOOT OR TWO MORE AS THE MEAN OF THE 
MODEL SURFACE WINDS ARE LOWER THAN THE OPERATIONAL GFS...AND THE GFS 
ENSEMBLE MEAN AND 21 UTC SREF SUPPORTS THIS IDEA OF LOWER 
WINDS.

&&

.FIRE WEATHER...
A LOW PRESSURE SYSTEM DEVELOPING OVER THE WESTERN GULF WILL MOVE
EASTWARD TODAY AND TONIGHT...ACCOMPANIED BY WIDESPREAD CLOUDS AND
SHOWERS. AFTER THIS LOW MOVES EAST OF THE AREA ON MONDAY...SHOWERS
WILL DIMINISH BUT CLOUDS WILL PERSIST..AS ANOTHER LOW PRESSURE
DEVELOPS FURTHER SOUTH OVER THE GULF. SOME DRIER AIR IS EXPECTED
TO FILTER INTO THE TRI-STATE AREA BY THE END OF THE WEEK.
HOWEVER...CRITICAL FIRE WEATHER CONDITIONS ARE NOT EXPECTED TO
DEVELOP UNTIL AT LEAST NEXT WEEKEND.

&&

.PRELIMINARY POINT TEMPS/POPS...
TALLAHASSEE   72  58  71  51  71 /  20  80  50  10  10 
PANAMA CITY   70  60  72  57  70 /  30  80  40  10  10 
DOTHAN        65  51  64  49  67 /  30  80  50  20  10 
ALBANY        66  53  64  49  68 /  20  80  60  20  10 
VALDOSTA      71  56  69  52  72 /  10  80  70  30  10 
CROSS CITY    76  57  76  58  77 /  10  70  60  20  10 
APALACHICOLA  71  62  73  57  70 /  20  70  40  10  10 

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
GA...NONE.
FL...NONE.
GM...NONE.

&&

$$

LONG TERM/AVIATION/FIRE WEATHER...DUVAL
REST OF DISCUSSION...FOURNIER

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