FXUS62 KTAE 240850
AFDTAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
350 AM EST THU DEC 24 2009
...STRONG TO SEVERE STORMS POSSIBLE LATE THIS AFTERNOON THROUGH
TONIGHT ACROSS THE REGION...
.SYNOPSIS...03 UTC SURFACE ANALYSIS SHOWS A STORM SYSTEM TAKING
SHAPE ACROSS THE SOUTHERN PLAINS. TWO SURFACE LOW ARE EVIDENT...ONE
NEAR AUSTIN TX AND ANOTHER JUST SOUTH OF KANSAS CITY. A COLD FRONT
CONNECTS THESE TWO LOWS WITH A WARM FRONT ANALYZED ACROSS THE
ARKLATEX SOUTHEASTWARD INTO THE NORTH CENTRAL GULF OF MEXICO.
LOCALLY...DEWPOINTS ARE IN THE 40S OVER THE INLAND AREAS TO NEAR 50
AT THE COAST. THE WARM FRONT AT ANALYSIS TIME HAD NOT ENTERED THE
COASTAL WATERS...SIGNIFYING THAT THE MOISTENING AND DESTABILIZATION
OF OUR AIRMASS HAS A WAYS TO GO.
UPPER AIR DATA AT 00 UTC SHOWS AN UPPER LOW MOVING INTO WEST TEXAS.
THIS UPPER LOW IS ALL PART OF A DEEPER TROF THAT IS NOW LOCATED
ACROSS THE EASTERN ROCKIES. A SECOND LOW IS DROPPING INTO EASTERN
MONTANA AND WILL...OVER TIME...MERGE WITH THIS UPPER LOW ACROSS THE
CENTRAL PLAINS. OF PARTICULAR CONCERN FOR OUR WEATHER IS THE
BEHAVIOR OF THIS PRIMARY UPPER LOW ACROSS TEXAS. THIS LOW IS PROGGED
TO STRENGTHEN AND TAKE ON A NEGATIVE TILT THROUGHOUT THE DAY. HOW
FAR THIS LOW PROGRESSES EASTWARD WILL GREATLY DETERMINE OUR SEVERE
WEATHER PROSPECTS TONIGHT.
&&
.SHORT TERM (TODAY THROUGH SATURDAY).
THERE IS A GREAT DEAL TO LOOK AT THIS MORNING. SINCE ANALYSIS TIME
AT 03 UTC...SURFACE DATA INDICATE THAT THE AREA OF LOW PRESSURE
ABOUT NEAR AUSTIN TEXAS HAS DEEPENED ABOUT 2 MB AND WITH THE UPPER
LOW DEEPENING ACROSS WEST TEXAS WHILE MOVING EAST...THUNDERSTORM
DEVELOPMENT HAS BECOME MORE CONCENTRATED ACROSS EAST TEXAS.
THUS...THE STRONG STORM SYSTEM THE MODELS HAVE BEEN PREDICTING IS
COMING TOGETHER ON TRACK. THE 24/00Z GFS AND NAM AS WELL AS THE
23/12Z EURO ARE REMARKABLY CLOSE ON THE PROGRESSION OF THE MID LEVEL
LOW...IF NOT THE INTENSITY. OF COURSE...THE BIG DIFFERENCE THIS
CYCLE COMPARED TO 24 HOURS AGO IS THAT THE MID LEVEL LOW MAKES IT A
LITTLE FURTHER EAST...PERHAPS AS FAR AS MEMPHIS...WHEREAS LAST NIGHT
THE LOW WAS STRUGGLING TO REACH LITTLE ROCK. THIS FURTHER EASTWARD
MOVEMENT PLACES OUR REGION IN AN AREA OF BETTER 500 MB HEIGHT FALLS
(ABOUT 40 M/12 HRS)...WHICH WILL PROVIDE A LITTLE BETTER DYNAMICAL
FORCING THAN SEEN IN THE MODELS YESTERDAY. HOWEVER...THE SURFACE
DATA FROM 03Z SHOW THAT THE MOIST AIRMASS OVER THE GULF HAS HAD
TROUBLE ADVECTING INLAND AND WITH 60 DEGREE DEWPOINTS JUST NOW
REACHING OUR BUOYS...THERE ARE SOME CONCERNS WITH THE QUALITY OF THE
AIRMASS ACROSS OUR REGION BY THE TIME THIS SYSTEM REACHES US IN THE
EVENING.
THIS LACK OF MEANINGFUL INSTABILITY IS GENERALLY HANDLED WELL BY THE
GLOBAL MODELS WHICH SHOW A DECREASING TREND IN ANY CONVECTIVE
ELEMENTS BY 06Z AS THE SQUALL LINE NEARS THE
APALACHICOLA/CHATTAHOOCHEE RIVERS. THE ONLY APPRECIABLE DIFFERENCES
BETWEEN THE NAM AND GFS RELATE TO PROGRESSION OF THE SYSTEM WITH THE
GFS CONTINUING TO BE JUST A LITTLE BIT FASTER. WITH THE TIMING
DIFFERENCE WORKING OUT TO BE AROUND 3 HOURS...WILL GENERALLY ACCEPT
THE GFS GUIDANCE THIS SET FOR OVERALL GRID POPULATION.
TODAY...STILL SEEING A RELATIVELY DRY AIRMASS IN PLACE IN THE MID
LEVEL ACROSS THE REGION THIS MORNING THAT WILL TAKE SOME TIME TO
MOISTEN. WHILE MOIST ISENTROPIC ASCENT IN THE 300-295K LAYER WILL
HELP MOIST THE AIRMASS CONSIDERABLY...I AM A LITTLE SUSPICIOUS OF
THE STRENGTH OF THE ASCENT SHOWN IN THE GFS. THUS...WILL GENERALLY
STAY A LITTLE BELOW MAV GUIDANCE POPS IN THE CENTRAL AND EASTERN CWA
WHERE ANY PRECIP WILL BE DRIVEN BY ISENTROPIC UPGLIDE. IN THE
WEST...WITH QG FORCING ASSISTING IN SHOWER DEVELOPMENT LATE IN THE
DAY...WILL STAY CLOSER TO GUIDANCE POPS. GIVEN THAT DEWPOINTS WILL
BE STRUGGLING TO REACH THE UPPER 50S BY 21Z...WILL ONLY MENTION
ISOLD T OVER THE LAND AREAS IN THE FLA PANHANDLE AND SOUTHEAST
ALABAMA AND SHOWERS ELSEWHERE.
THERE IS SOME CONCERN THAT SOME DISCRETE CELLS MAY TRY AND DEVELOP
AHEAD OF THE SQUALL LINE AND MOVE TOWARD THE PANHANDLE COAST IN THE
AFTERNOON HOURS...MAINLY AFTER 20Z. BASED ON INSTABILITY
PROFILES...IT APPEARS AS THOUGH ANY OF THESE CELLS WOULD BECOME
GRADUALLY ELEVATED WHILE MOVING TOWARD OUR COAST LINE IN THE
AFTERNOON HOURS...AS THE BEST INSTABILITY WILL LIKELY OCCUR IN THE
EVENING AS THE SQUALL LINE GETS CLOSER TO THE REGION.
DUE TO GRADIENT WINDS INCREASING AHEAD OF THIS SYSTEM...WILL ISSUE A
LAKE WIND ADVISORY FOR TODAY THROUGH SUNSET. THEREAFTER...STRONG
WINDS WILL BEGIN TO BE ASSOCIATED WITH SHOWERS AND STORMS...SO WILL
LET THIS PRODUCT EXPIRE AT THAT TIME.
TONIGHT...BETTER DYNAMICS AND INSTABILITY WILL BEGIN TO COME
TOGETHER AFTER 23Z ACROSS THE REGION AND RESULT IN AN INCREASING
THREAT FOR SEVERE WEATHER. DEEP LAYER 0-6 KM SHEAR OVER 60 KNOTS
IS MORE THAN SUFFICIENT FOR ROTATING UPDRAFTS AND ORGANIZED
CONVECTIVE LINES. THE IMPRESSIVE 850 MB LLJ IS STILL PROGGED TO
BRUSH AGAINST OUR WESTERN CWA AROUND 65 KNOTS. THUS...AS IS
TYPICAL...THE KINEMATICS ARE MORE THAN FAVORABLE FOR SEVERE WEATHER.
THE INSTABILITY SIDE OF THE EQUATION IS MORE SUSPECT. WITH DEWPOINTS
PROGGED TO BARELY REACH THE LOW 60S...AVAILABLE SURFACE BASED
INSTABILITY WILL BE LIMITED. IT LOOKS THAT THE BEST INSTABILITY WILL
BECOME FOCUSED IN THE EVENING JUST AHEAD OF THE COLD FRONT AND PEAK
SOMEWHERE BETWEEN 500 J/KG TO 750 J/KG...MAINLY FROM I-10 SOUTHWARD.
FURTHER NORTHWARD...THE POTENTIAL FOR SURFACE-BASED INSTABILITY
GREATER THAN 250 J/KG DECREASES...BUT WITH BETTER HEIGHT
FALLS...FORCING MAY OVERCOME THE DEFICIENT INSTABILITY AND SUSTAIN
THE PROGRESSION OF THE SQUALL LINE INTO SOUTHEAST ALABAMA AND
SOUTHWEST GEORGIA. THUS...THE BEST POTENTIAL FOR SEVERE WEATHER WILL
BE IN THE FLORIDA PANHANDLE PRIOR TO 06Z WHERE THE INSTABILITY AND
SHEAR WILL OVERLAP. AFTER 06Z...CONVECTIVE ACTIVITY MOVES INTO SOUTH
CENTRAL GEORGIA AND THE FLORIDA BIG BEND...BUT AT THIS TIME THE
BETTER DYNAMICS WILL BE LIFTING OUT. HOWEVER...THERE MAY BE ENOUGH
OF AN OVERLAP BETWEEN THE DYNAMICS AND MEAGER INSTABILITY TO
CONTINUE TO SUPPORT STRONG TO SEVERE STORMS ALL THE WAY TO I-75 BY
12Z...THUS WILL CONTINUE MENTION OF SEVERE WEATHER IN ALL AREAS
UNTIL DAYBREAK. IT GOES WITHOUT SAYING THAT POPS FOR THIS PERIOD ARE
100 PERCENT.
CHRISTMAS DAY...THE FRONTAL BOUNDARY WILL BE EXITING THE AREA JUST
AFTER DAYBREAK WITH DRIER AIR...BUT ONLY MARGINALLY COOLER AIR
ARRIVING. WILL HOLD OVER POPS ACROSS THE EASTERN HALF OF THE REGION
UNTIL 18Z...BUT WILL LIKELY SEE ANY RAIN CHANCES END BY 15Z WITH
PARTLY CLOUDY TO MOSTLY CLEAR SKIES AREA WIDE BY 18Z.
FRIDAY EVENING AND BEYOND...A DRIER AIRMASS AND A LITTLE MORE COOLER
AIR WILL ARRIVE. WITH THE MID AND UPPER LEVEL FLOW BECOMING MORE
SOUTHWESTERLY...THE POTENTIAL FOR CIRRUS TO OVERSPREAD THE AREA
EXISTS...AND THIS MAY HOLD BACK AFTERNOON TEMPERATURES ON SATURDAY
INTO THE UPPER 50S.
.LONG TERM (SUNDAY THROUGH THURSDAY).
BY SUNDAY MORNING...THE COLD FRONT FROM CHRISTMAS EVE THROUGH
CHRISTMAS MORNING WILL POSITION ITSELF OVER CENTRAL FLORIDA WELL
AWAY FROM OUR AREA. THIS WILL ALLOW A RIDGE OF COOL HIGH PRESSURE TO
SETTLE IN WITH DRIER MORE SEASONABLE CONDITIONS THROUGH TUESDAY OF
NEXT WEEK. THERE IS STILL MODEL INCONSISTENCY REGARDING THE NEXT
SYSTEM TO IMPACT THE REGION. THE EURO SHOWS AN UPPER LOW FORMING
OVER THE CENTRAL STATES WITH AN ATTENDANT SURFACE LOW FORMING IN THE
WESTERN GULF WEDNESDAY MORNING. THIS LOW IS THEN FORECAST TO MOVE
ALONG THE NORTHERN GULF COAST BRINGING A SOLID CHANCE OF RAIN FROM
THURSDAY NIGHT INTO FRIDAY. THE GFS DEPICTS THE DEVELOPMENT OF A
WEAKER GULF LOW FORMING IN THE WEST-CENTRAL GULF ON THURSDAY NIGHT.
THE LOW THEN PROPAGATES EASTWARD TOWARD THE CENTRAL FLORIDA
PENINSULA. THIS WOULD YIELD LESS TOTAL PRECIPITATION AS OUR AREA
WOULD REMAIN JUST NORTH OF THE HEAVIEST RAINFALL. BOTH SOLUTIONS
AGREE ON SURFACE LOW FORMATION BUT OVERALL TIMING AND DEGREE OF
CONVECTIVE POTENTIAL IS STILL UNCERTAIN. FOR NOW...SILENT 10% POPS
HAVE BEEN ISSUED THROUGH WEDNESDAY MORNING WHEN CLOUD COVER AND RAIN
CHANCES SHOULD INCREASE DEPENDING ON DEVELOPING GULF LOW. POPS WERE
THEN INCREASED TO 20% TO 30% FROM WEDNESDAY AFTERNOON THROUGH
THURSDAY AFTERNOON WITH A NORTH-SOUTH GRADIENT TO DEPICT LIKELY
PRECIPITATION PATTERN. 20% POPS WILL CARRY THE END OF THE PERIOD DUE
TO A SLOWER PROGRESSION OF THE LOW AS SHOWN IN THE GFS. AS HIGH
PRESSURE SETTLES INTO OUR AREA WITH NORTHERLY FLOW...TEMPS WILL
REMAIN BELOW CLIMO THROUGH THE FIRST PART OF THE EXTENDED CYCLE WITH
HIGHS IN THE UPPER 50S TO NEAR 60 AND LOWS AVERAGING IN THE LOWER
30S. FREEZING TEMPERATURES WILL ALSO BE POSSIBLE MONDAY AND TUESDAY
NIGHTS. GRADUAL WARMING IS EXPECTED AHEAD OF THE PREDICTED SURFACE
LOW AS WINDS SHIFT AND MOISTURE INCREASES BEGINNING WEDNESDAY.
OVERALL...PLEASANT WEATHER IS EXPECTED FOR THE LONG TERM WITH COOLER
WINTER TEMPERATURES FOR MUCH OF THE PERIOD.
&&
.AVIATION...WITH THE EXCEPTION OF VLD...VFR CIGS/VSBYS WILL CONTINUE
FOR THE NEXT FEW HOURS. AS MOIST AIR CONTINUES TO MOVE INTO THE
AREA...EXPECT LOW CLOUDS TO DEVELOP AND CIGS/VSBYS TO LOWER TO
MVFR/IFR LEVELS BY EARLY THURSDAY MORNING WITH FOG. AS WE MOVE INTO
THE AFTERNOON...VSBYS WILL IMPROVE...BUT CIGS WILL REMAIN IN THE
MVFR/IFR CATEGORY. GUSTY WINDS OF UP TO 25 TO 30 KT WILL BE POSSIBLE
AHEAD OF AN ADVANCING STORM SYSTEM SET TO MOVE THROUGH THE AREA BY
FRIDAY MORNING. A LINE OF THUNDERSTORMS IS EXPECTED TO DEVELOP AND
PUSH THROUGH THE AREA BY CHRISTMAS MORNING BRINGING THE POTENTIAL
FOR DAMAGING WINDS AND HEAVY RAINFALL. EXPECT MVFR/IFR CONDITIONS
EXCEPT IN THUNDERSTORMS BOTH AHEAD OF AND WITHIN THE CONVECTIVE LINE
WHERE LIFR CONDITIONS WILL BRIEFLY BE POSSIBLE OVERNIGHT THURSDAY
NIGHT INTO CHRISTMAS DAY.
&&
.MARINE...SMALL CRAFT ADVISORY CONDITIONS CONTINUE OVER MUCH OF THE
MARINE AREA. EXPECT THESE SCA CONDITIONS TO BUILD INTO THE FAR
EASTERN LEGS OF THE MARINE AREA BY LATE MORNING...SO WILL ISSUE A
SCA FOR THESE AREAS. WINDS WILL STRENGTHEN OUT OF THE SOUTH LATER
TODAY AND BEGIN TO DRIVE SURF HEIGHTS ACROSS THE PANHANDLE BEACHES
TO 6 TO 8 FEET...SO WILL BE ISSUING A HIGH SURF ADVISORY FOR THESE
AREAS. WINDS MAY GUST TO GALE FORCE ON THURSDAY EVENING AHEAD OF THE
SQUALL LINE BEFORE SHIFTING TO THE WEST BEHIND THIS FEATURE. SEAS
MAY PEAK OVER 12 FEET THURSDAY NIGHT NEAR THE PEAK OF THE EVENT.
WINDS WILL BEGIN TO DECREASE ON FRIDAY AFTERNOON AS AN AREA OF HIGH
PRESSURE MOVES EASTWARD INTO THE REGION. A WEAK BOUNDARY WILL MOVE
THROUGH THE MARINE AREA ON MONDAY AND MAY BRIEFLY STRENGTHEN
OFFSHORE WINDS TO THE CAUTIONARY LEVELS BEFORE SUBSIDING ON AGAIN ON
WEDNESDAY.
&&
.FIRE WEATHER...THE DOMINANT HIGH PRESSURE SYSTEM IS BEGINNING ITS
TREK NORTHEASTWARD AS AN AREA OF LOW PRESSURE CONTINUES TO
STRENGTHEN TO OUR WEST. WINDS HAVE SHIFTED TO THE EAST AND WILL
CONTINUE TO VEER TO SOUTHEAST AHEAD OF THIS SYSTEM. A COLD FRONT IS
EXPECTED TO CROSS OUR AREA THURSDAY NIGHT INTO CHRISTMAS MORNING
WITH A LINE OF STRONG TO POSSIBLY SEVERE THUNDERSTORMS EXITING THE
AREA BY EARLY CHRISTMAS DAY. WITH A STRONG LOW-LEVEL WIND FIELD OFF
THE GULF...THE LOW LEVELS WILL MAINTAIN HIGH MOISTURE CONTENT SO NO
FIRE WEATHER CONCERNS ARE ANTICIPATED THROUGH FRIDAY. ONCE THE FRONT
HAS PASSED...DRIER AIR WILL MOVE IN. RED FLAG CONDITIONS MAY BE
POSSIBLE ON SATURDAY AS SUFFICIENT HEATING LEADS TO RELATIVE
HUMIDITY BELOW CRITICAL LEVELS.
&&
.PRELIMINARY POINT TEMPS/POPS...
TALLAHASSEE 69 56 65 37 59 / 40 100 30 0 0
PANAMA CITY 68 54 61 38 57 / 80 100 10 0 0
DOTHAN 67 48 58 33 55 / 80 100 10 0 0
ALBANY 67 54 63 31 56 / 40 100 30 0 0
VALDOSTA 71 59 68 37 57 / 30 100 60 0 0
CROSS CITY 74 61 70 40 62 / 30 100 60 0 0
APALACHICOLA 68 57 65 39 56 / 60 100 10 0 0
&&
.TAE WATCHES/WARNINGS/ADVISORIES...
AL...LAKE WIND ADVISORY FROM 9 AM THIS MORNING TO 6 PM CST THIS
EVENING FOR THE FOLLOWING ZONES: COFFEE...DALE...GENEVA...
HENRY...HOUSTON.
GA...LAKE WIND ADVISORY FROM 10 AM THIS MORNING TO 7 PM EST THIS
EVENING FOR THE FOLLOWING ZONES: BAKER...BEN HILL...
BERRIEN...BROOKS...CALHOUN...CLAY...COLQUITT...COOK...
DECATUR...DOUGHERTY...EARLY...GRADY...IRWIN...LANIER...
LEE...LOWNDES...MILLER...MITCHELL...QUITMAN...RANDOLPH...
SEMINOLE...TERRELL...THOMAS...TIFT...TURNER...WORTH.
FL...LAKE WIND ADVISORY FROM 10 AM EST /9 AM CST/ THIS MORNING TO 7
PM EST /6 PM CST/ THIS EVENING FOR THE FOLLOWING ZONES:
BAY...CALHOUN...COASTAL WALTON...DIXIE...FRANKLIN...
GADSDEN...GULF...HOLMES...INLAND WALTON...JACKSON...
JEFFERSON...LAFAYETTE...LEON...LIBERTY...MADISON...TAYLOR...
WAKULLA...WASHINGTON.
HIGH SURF ADVISORY FROM 7 PM THIS EVENING TO 1 PM EST FRIDAY
FOR THE FOLLOWING ZONES: FRANKLIN.
HIGH SURF ADVISORY FROM NOON TODAY TO 6 PM CST FRIDAY FOR THE
FOLLOWING ZONES: BAY...COASTAL WALTON...GULF.
GM...SMALL CRAFT ADVISORY FROM 10 AM EST THIS MORNING TO 7 PM
EST FRIDAY FROM THE OCHLOCKONEE RIVER ENTRANCE TO THE SUWANNEE
RIVER ENTRANCE OUT TO 20 NAUTICAL MILES.
SMALL CRAFT ADVISORY UNTIL 7 AM EST SATURDAY FROM DESTIN TO THE
OCHLOCKONEE RIVER ENTRANCE OUT TO 60 NAUTICAL MILES.
&&
$$
AVIATION...GOULD
LONG TERM...AUSTIN
REST OF DISCUSSION...GODSEY
