FXUS64 KHUN 242316 AAA
AFDHUN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE HUNTSVILLE AL
515 PM CST THU DEC 24 2009

.UPDATE...FOR 00Z TAFS/AVIATION DISCUSSION
&&

.AVIATION...STRONG SE WINDS WILL CONTINUE AROUND 25KT WITH GUSTS 
NEAR 40KT THROUGH THE EVENING HRS...AND TOWARD 12Z FRI BEFORE WINDS 
BEGIN TO GRADUALLY DIMINISH. AN AREA OF MOD TO HEAVY SHRA WILL ALSO 
BEGIN TO MOVE INTO NW AL AROUND 03Z...AND CONTINUE EWD ACROSS THE 
REMAINDER OF THE AREA THROUGH 09Z...BEFORE EXITING TOWARD THE E. 
CEILINGS/VIS WILL ALSO BEGIN TO FALL TOWARD MVFR LEVELS WITH THE 
APPROACHING SHRA...AND MAY LOWER TO IFR CRITERIA IN AREAS OF +SHRA. 
CEILINGS LOOK TO REMAIN NEAR MVFR CRITERIA PAST 12Z WITH SFC WINDS 
SHIFTING TOWARD THE SW AROUND 15KT.
&&

.DISCUSSION...ITS AN INTERESTING FORECAST TONIGHT ACROSS MUCH OF THE 
SOUTHEAST...AND THE CENTRAL TENNESSEE VALLEY IS NO EXCEPTION AS ALL 
EYES ARE FOCUSED ON THE SQUALL LINE TRUCKING ACROSS THE LOWER 
MISSISSIPPI VALLEY. EARLIER TODAY...OPTED TO HOIST A HIGH WIND 
WARNING AREA-WIDE AS GRADIENT WINDS CONTINUED TO STRENGTHEN AS 
PRESSURE COUPLETS TIGHTENED AND LATEST MODEL RUNS SUGGESTED 
EXTREMELY HIGH WIND SPEEDS />50KT/ AT THE TOP OF THE BOUNDARY LAYER 
AND H85 WINDS APPROACHING 85KT. SINCE THEN...AREA WIND OBS HAVE 
REGISTERED PEAK GUSTS IN THE UPPER 30S/MID 40 MPH RANGE...WITH 
LATEST OB FROM TUPELO MS PICKING UP A 49 MPH GUST. NAM CONTINUES TO 
INDICATE THAT SPEEDS WILL STRENGTHEN JUST AHEAD OF THE APPROACHING 
SQUALL LINE...SO LOOK FOR WINDS TO INCREASE THROUGH THE REMAINDER OF 
THE AFTERNOON HOURS AND INTO THE EVENING. IN FACT...LATEST /18Z/ NAM 
SHOWS A MUCH SLOWER EASTWARD PROGRESSION OF THE SQUALL LINE /AS 
COMPARED TO THE 12Z NAM AND GFS/...WHICH IS LIKELY IN RESPONSE TO 
ALMOST DUE SOUTHERLY FLOW AT H5...SO THERE IS POTENTIALLY A LONGER 
PERIOD OF TIME FOR HIGH WINDS. MOTORISTS ARE URGED TO USE CAUTION 
WHILE TRAVELING THIS HOLIDAY EVENING AS BRANCHES AND SMALL TREES MAY 
EASILY BE TOPPLED WITH HIGH WINDS...ESPECIALLY OVER THE HIGHER 
TERRAIN LOCATIONS. 

WHILE SOME SHOWERS HAVE DEVELOPED OVER THE LAST TWO HOURS ACROSS THE 
AREA...THERE HAS OTHERWISE BEEN VERY LITTLE PRE-FRONTAL 
PRECIPITATION ASSOCIATED WITH THIS SYSTEM...WHICH IS VERY GOOD NEWS 
FOR THE FLASH FLOOD THREAT. INDEED...BEST MOISTURE TRANSPORT AND 
H85/H7 THETAE RIDGE REMAIN SOUTH OF HERE...LOOSELY ASSOCIATED WITH 
EXPANDING AREA OF RELATIVELY COOL CLOUD TOPS CURRENTLY OBSERVED OVER 
SOUTH/CENTRAL MISSISSIPPI. THAT SAID...UPSTREAM OBSERVED RAIN 
RATES...IN CONJUNCTION WITH OUR WET SOILS...CERTAINLY WARRANTS 
MAINTAINING THE CURRENT FLASH FLOOD WATCH AS A QUICK ONE OR TWO 
INCHES OF RAINFALL IS EXPECTED FROM THE SQUALL LINE AS IT MOVES 
THROUGH. SOME LOCATIONS MAY SEE UPWARDS OF THREE INCHES...BUT THESE 
REPORTS SHOULD BE ISOLATED.

AS IF THE AMBIENT WIND/FLASH FLOODING THREATS WERE NOT ENOUGH ON 
CHRISTMAS EVE...THERE IS ALSO THE OUTSIDE CHANCE FOR THUNDERSTORMS 
JUST ALONG THE LINE THIS EVENING. IN FACT...0-3K SRH IS WELL OVER 
1000 M2/S2 THROUGH MIDNIGHT...BUT ZERO SURFACE BASED INSTABILITY 
/AND ONLY LIMITED ELEVATED INSTABILITY/ SHOULD KEEP THE THUNDERSTORM 
COVERAGE LIMITED. NEVERTHELESS...ANY CONVECTIVE ACTIVITY THIS 
EVENING WILL LOCALLY EXACERBATE THE HIGH WIND AND FLASH FLOODING 
THREAT. 

AS THE MAIN LINE PROGRESSES EASTWARD ACROSS THE VALLEY /REACHING THE 
AL/GA BORDER AROUND 08Z/...WINDS WILL SHIFT MORE SOUTHERLY...BUT 
REMAIN GUSTY THROUGH THE OVERNIGHT HOURS...WITH THE MAIN COLD FRONT 
ARRIVING CHRISTMAS MORNING SIGNALED BY A WIND SHIFT TO THE WEST 
ALONG WITH MUCH COLDER TEMPERATURES ARRIVING FROM THE PLAINS. IN 
FACT...WHILE THERE WON/T BE ENOUGH MOISTURE FOR A TRUE WHITE 
CHRISTMAS AREAWIDE...A FEW LOCATIONS MAY SEE A FEW FLAKES OR 
FLURRIES TOMORROW MORNING /ESPECIALLY IN THE NORTHWEST/. BUFR 
SOUNDINGS SHOW THAT THE ATMOSPHERE IS ONLY SATURATED TO ABOUT 
-10C...SO DESPITE THE SMALL AMOUNT OF MORNING CAPE...WE WILL NOT SEE 
ANYTHING MEASURABLE IN OUR NECK OF THE WOODS.

BREEZY CONDITIONS WILL LINGER FOR MUCH OF CHRISTMAS DAY AS 
POST-FRONTAL CAA FLOWS INTO THE CWFA...BUT THE NEXT CHANCE FOR 
PRECIPITATION SHOULD HOLD OFF UNTIL THE NEW YEARS HOLIDAY /ALTHOUGH 
A MOSTLY DRY COLD FRONT MAY BRING A FEW FLURRIES TO THE CUMBERLAND 
PLATEAU SUNDAY NIGHT/. THERE IS PRETTY POOR AGREEMENT BETWEEN THE OP 
GFS AND THE ECMWF...SO ADDED IN A SLIGHT CHANCE OF A RAIN/SNOW MIX 
FOR NEW YEARS EVE...BUT GIVEN THE HIGH DEGREE OF UNCERTAINLY IN THE 
TRACK OF THE DEVELOPING SURFACE LOW...CONFIDENCE IS LOW ATTM.

AND ONE LAST NOTE FROM ALL OF US AT WFO HUNTSVILLE...HAPPY HOLIDAYS 
TO YOU AND YOURS!
&&

.HUN WATCHES/WARNINGS/ADVISORIES...
AL...HIGH WIND WARNING UNTIL 2 AM CST FRIDAY FOR THE FOLLOWING 
ZONES:      COLBERT...CULLMAN...DEKALB...FRANKLIN 
AL...JACKSON...     
LAUDERDALE...LAWRENCE...LIMESTONE...MADISON...MARSHALL...     MORGAN.

     FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR THE FOLLOWING ZONES: 
     COLBERT...CULLMAN...DEKALB...FRANKLIN AL...JACKSON...
     LAUDERDALE...LAWRENCE...LIMESTONE...MADISON...MARSHALL...
     MORGAN.

TN...HIGH WIND WARNING UNTIL 2 AM CST FRIDAY FOR THE FOLLOWING 
ZONES:      FRANKLIN TN...LINCOLN...MOORE.

     FLASH FLOOD WATCH THROUGH LATE TONIGHT FOR THE FOLLOWING ZONES: 
     FRANKLIN TN...LINCOLN...MOORE.

&&

$$

UPDATE...09
DISCUSSION...JLL