FXUS62 KTAE 111418
AFDTAE

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
915 AM EST FRI DEC 11 2009

...CHILLY AND CLOUDY DAY TODAY...

...INCREASING RAIN CHANCES REST OF WEEKEND...

.SYNOPSIS...
AT 9 AM EST...SKIES REMAINED CLOUDY ACROSS THE REGION WITH CIGS 
MAINLY 7-10K WITH CIRRUS COVER ABOVE. SOME LIGHT DRIZZLE AND 
SPRINKLES OCCURRING INTERMITTENTLY ACROSS REGION. TEMPS REMAINED ON 
COOL SIDE...FROM UPPER 30S SE ALA TO MID 40S COAST. 24 HR TEMP/DEW 
POINT COMPARISON INDICATES SIGNIFICANT AIRMASS CHANGE FROM W-E. WEST 
OF APALACHICOLA RIVER...TEMPS RUNNING 1 TO 5 DEGREES COLDER AND 8 TO 
11 DEGREES DRIER THAN SAME TIME YESTERDAY. EAST OF APALACHICOLA 
RIVER TEMPS RUNNING 7-10 DEGREES COLDER AND 15 TO 20 DEGREES DRIER 
THAN SAME TIME YESTERDAY. WINDS WERE NE 6 MPH TO 13 MPH WITH HIGHER 
GUSTS SOUTH.  

AT UPPER LEVELS...
THE LARGE SCALE CONUS SPLIT FLOW PATTERN CONTINUES OVER THE ERN PAC 
AND WRN N AMERICA WITH CONFLUENT FLOW DOWNSTREAM OVER THE ERN U.S. 
WHERE WE SEE A 175-KT UPPER JET OVER THE TN/KY REGION. SRN STREAM 
JET WILL PERSIST FROM OFF THE CNTRL/SRN CA CST ESE TO WRN GULF 
COAST. SATELLITE IMAGERY INDICATES PLENTY OF UPPER LEVEL CLOUDS 
SCOOTING SW-NE ACROSS THE GULF COAST STATES S OF THE JET...AND WE 
ARE ALSO SEEING AN EXPANDING MID LEVEL DECK OVER N FL AND THE NRN 
GULF. BEGINNING THIS EVE...THE GULF OF ST LAWRENCE LOW WILL MOVE 
NEWD AND THE NRN SASKATCHEWAN LOW ELONGATES WEST-TO-EAST. AS A 
RESULT...THE BROAD UPPER TROUGH OVER THE ERN TWO THIRDS OF THE 
COUNTRY WILL DEAMPLIFY WITH THE FLOW BECOMING INCREASINGLY ZONAL 
ACROSS U.S. LATER BY THIS EVE.   

AT LOWER LEVELS...
ANALYSIS SHOWS THAT LOCAL AREA REMAINS BETWEEN COLD HIGH PRESSURE 
CENTERED OVER THE LOWER MS AND TN VALLEYS AND WEDGING DOWN THE EAST 
COAST...AND A COLD FRONT THAT HAS SINCE ZIPPED DOWN THE PENINSULA 
AND IS NOW APPROACHING THE KEYS. A WEAK AREA OF LOW PRESSURE IS 
SHOWING SIGNS OF DEVELOPMENT AND SHOULD DRIFT NWD ON THE WRN END 
OF THIS FRONT OVER THE SWRN GULF OF MEXICO. THIS COMBINATION WILL 
PROVIDE FOR A CHILLY DAY (AS REFLECTED ABOVE) WITH TIGHT GRADIENTS.  

WEAK ISENTROPIC ASCENT WILL CONTINUE THE EXPANSION OF THE MID LEVEL 
CLOUD DECK NWD REST OF THIS MORNING INTO AFTN AS CLOUD BASES 
GRADUALLY LOWER. HOWEVER...EVEN AS MID AND UPPER LEVELS BECOME 
SATURATED...LOWER LEVELS WILL REMAIN QUITE DRY DURING THE REST OF 
THIS MORN. THIS REFLECTED IN 12Z RAOBS...I.E TAE WITH ONLY 0.79 
INCH PWAT. SO THE RAIN THAT INITIALLY FALLS FROM THE CLOUDS WILL 
EVAPORATE AS VIRGA REINFORCING THE ALREADY COOL AIR MASS CURRENTLY 
IN PLACE. THEN...AS A WEAK UPPER SHORTWAVE MOVES OVER THE NORTHERN 
GULF COAST TONIGHT...THERE WILL BE AN INCREASE IN CLOUD COVER FROM 
SW-NE...MOISTENING OF THE BOUNDARY LAYER WITH MORE OVERRUNNING RAIN 
HITTING THE GROUND. THEN...ANOTHER SHORTWAVE OVER THE PLAINS MOVES 
TOWARDS THE AREA ON SAT...SUPPORTING A FURTHER INCREASE IN THE 
CHANCES FOR RAIN. WITH A COLD AIRMASS OVER THE NORTHERN GULF 
COAST...THE PRECIP LOOKS TO REMAIN LARGELY ISENTROPIC IN NATURE. 
THIS ALL REFLECTED IN REGIONAL MODEL SOUNDINGS .I.E. GFS TAE WITH 
0.89 INCH PWAT AT 12 FRI INCREASING TO 1.73 INCH PWAT AT 00Z SUN AS 
WARM FRONT LIFTS ACROSS AREA.  

MODEL GUIDANCE SHOWS COLD SURFACE HIGH SHIFTING TO SRN MID-ATLC 
COAST ON SAT AND THEN OFF CAROLINA COAST SATURDAY NIGHT. AT SAME 
TIME...IMPULSE NOW EXITING EWD FROM CA EXPECTED TO MOVE STEADILY 
E/ESE REACHING W TX BY 12Z SAT. THIS WILL INDUCE FURTHER 
CYCLOGENESIS (SURFACE LOW) ALONG WRN END OF STALLED FRONT OVER THE 
CNTRL/NRN GULF OF MEXICO. FORCING WILL BECOME STRONGER DURING THE 
DAY AS A SURFACE LOW BEGINS TO DEVELOP. AS THE WEAK LOW OVER THE 
WESTERN GULF MOVES INLAND OVER LOUISIANA AND MISSISSIPPI BY EVE...A 
SSW LOW LEVEL JET WILL STRENGTHEN OVER THE LOWER MS THROUGH NRN GULF 
DOWNSTREAM FROM THE PROGRESSIVE SRN STREAM SHORTWAVE TROUGH. AS THE 
SAME TIME...ERN HIGH LOSES ITS INFLUENCE ON LOCAL AREA AND...AND AS 
LOW LEVEL WARM AIR ADVECTION CONTINUE TO STRENGTHEN...THE WARM FRONT 
SHOULD BEGIN TO MOVE FURTHER INLAND AND TEMPERATURES WILL ACTUALLY 
RISE THROUGH THE NIGHT WITH LOW TEMPS OCCURRING AT THE VERY 
BEGINNING OF THE EVENING.

&&

.SHORT TERM...THIS AFTERNOON THROUGH SATURDAY...
THIS AFTERNOON...ENOUGH MOISTENING WILL OCCUR THAT A FEW DROPS WILL 
BE ABLE TO REACH THE GROUND. AND POPS RANGE FROM 40 FAR SE TO SILENT 
10 OVER OUR NRN TIER ZONES. MAX TEMPS WILL BE HELD IN THE 40S TODAY 
OVER MOST OF THE FORECAST AREA...EXCEPT ALONG THE COAST AND IN THE 
SE BIG BEND...AND EVEN THESE AREAS WILL ONLY PEAK IN THE LOWER 50S.

TONIGHT...ISENTROPIC ASCENT WILL CONTINUE TO INCREASE AND THE 
LOW LEVEL DRY AIR SHOULD BE COMPLETELY GONE SOMETIME AFTER MIDNIGHT. 
POPS WERE KEPT IN THE LIKELY RANGE FOR ALL BUT OUR NRN TIER GA 
ZONES. THE MIN TEMP TONIGHT IS EXPECTED BEFORE MIDNIGHT WITH TEMPS 
RISING THEREAFTER. 

SATURDAY...
STRONG AND DEEP ISENTROPIC LIFT WILL PERSIST THROUGH THE DAY 
ESPECIALLY ACROSS NW THIRD OF LOCAL AREA. UPSTREAM FORECAST 
SOUNDINGS ARE SHOWING CLOSE TO 500 J/KG OF ELEVATED INSTABILITY TO 
AROUND 900 MB. SO...WE SHOULD SEE SOME THUNDER EMBEDDED IN THE 
STRATIFORM RAIN SHIELD ABOVE THE STABLE SURFACE LAYER. THE 
CONVECTIVE POTENTIAL WILL LEAD TO THE POSSIBILITY OF SOME LOCALLY 
HEAVY RAINFALL. CATEGORICAL POPS EVERYWHERE. THERE EVEN REMAINS A 
AT BEST MARGINAL THREAT OF ROTATING STORMS SOUTH OF ADVANCING WARM 
FRONT WHERE VEERING LOW LEVEL WIND PROFILES WILL EXIST. HOWEVER... 
WEAK FORCING AND THE MARGINAL THERMODYNAMIC ENVIRONMENT IN WARM 
SECTOR WILL LIKELY SERVE AS LIMITING FACTORS FOR A SEVERE THREAT. 
RAIN WILL DECREASE FROM SOUTH TO NORTH BY NIGHT LEAVING AREAS OF FOG 
ACROSS ENTIRE REGION. 

&&

.MARINE...THIS AFTERNOON THROUGH EARLY SAT.
MID-MORNING OFFSHORE BUOYS SHOWS WINDS 20-25 KTS WITH GUSTS 
APPROACHING 30 KTS AND SEAS 6 TO 8 FEET. SO SCA LOOKS GOOD. AS THE 
COLD ADVECTION CONTINUES TO CREATE EFFICIENT MIXING OVER THE 
RELATIVELY MILD GULF WATERS. THE LATEST WRF RUN INDICATES WINDS 
STAYING ABOVE 20 KT UNTIL MIDDAY. AFTER A BRIEF LULL...WINDS PICK 
BACK UP THIS EVENING. WE THEREFORE KEPT THINGS SIMPLE AND MAINTAINED 
THE ADVISORY THROUGH 12Z SAT. AFTER THE WARM FRONT LIFTS N OF THE 
AREA...WINDS WILL VEER TO ONSHORE AND DIMINISH.

&&

.AVIATION...VFR TODAY WITH MID LEVEL CLOUD DECK OVER THE AREA. 
OVERNIGHT CLOUDS WILL THICKEN AN LOWER WITH SOME AREAS OF 
PRECIPITATION STREAMING INTO AREA. SOME LOWER CLOUDS COULD GO BROKEN 
BY EARLY SATURDAY RESULTING IN MVFR CONDITIONS. 

&&

.FIRE WEATHER...DESPITE HIGH TEMPS IN THE MID-UPPER 40S TODAY...DEW 
POINTS IN THE MID-UPPER TEENS WILL RESULT IN LONG DURATIONS OF 
SUB-35 PERCENT RELATIVE HUMIDITY FROM LATE MORNING THROUGH AFTERNOON
FOR ALL BUT TAYLOR...LAFAYETTE AND DIXIE COUNTIES IN NORTHWEST 
FLORIDA. ACROSS THE NORTHERN TIER COUNTIES OF SOUTHEAST ALABAMA AND 
SOUTHWEST GEORGIA...DURATIONS OF SUB-25 PERCENT RELATIVE HUMIDITY 
WILL BE THREE HOURS THIS AFTERNOON. ABUNDANT LOW LEVEL MOISTURE AND 
HIGH RAIN CHANCES WILL PRECLUDE RED FLAG CONCERNS THIS WEEKEND.

&&

.HYDROLOGY...THE CHOCTAWHATCHEE RIVER AT BRUCE IS NOW BELOW ITS 
MODERATE FLOOD STAGE AND CONTINUES A SLOW RECESSION. STAGES WILL 
LIKELY CONTINUE TO FALL INTO TONIGHT. THE APALACHICOLA RIVER AT 
BLOUNTSTOWN REMAINS A FEW FEET ABOVE FLOOD STAGE...BUT IS ALSO IN 
SLOW RECESSION. LOCALLY HEAVY RAINFALL ON SAT COULD REVERSE THESE 
TRENDS.

&&

.TAE WATCHES/WARNINGS/ADVISORIES...
AL...NONE.

GA...NONE.

FL...RED FLAG WARNING 16-23Z TODAY FOR THE FOLLOWING ZONES:
     BAY...CALHOUN...COASTAL WALTON...FRANKLIN...GADSDEN...GULF...   
     HOLMES...INLAND WALTON...JACKSON...JEFFERSON...LEON...
     LIBERTY...MADISON...WAKULLA...WASHINGTON.

GM...SMALL CRAFT ADVISORY UNTIL 12Z SATURDAY FOR THE FOLLOWING  
     ZONES: COASTAL WATERS FROM OCHLOCKONEE RIVER TO APALACHICOLA FL 
     OUT TO 20 NM...COASTAL WATERS FROM APALACHICOLA TO DESTIN FL    
     OUT 20 NM...WATERS FROM SUWANNEE RIVER TO APALACHICOLA FL FROM  
     20 TO 60 NM...WATERS FROM APALACHICOLA TO DESTIN FL FROM 20 TO  
     60 NM. 

&&

$$

AVIATION/FIRE WX...GOREE/M BARRY
PUBLIC/MARINE...BLOCK