FXUS62 KTAE 300826
AFDTAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
326 AM EST MON NOV 30 2009
...STRONG STORM SYSTEM WITH A MULTIFACETED HAZARDOUS WEATHER THREAT
TO AFFECT THE REGION TUESDAY NIGHT THROUGH WEDNESDAY...
.SYNOPSIS...04 UTC SURFACE ANALYSIS SHOWS A COLD FRONT EXTENDING
FROM THE EASTERN GREAT LAKES SOUTHWESTWARD TO THE LOW MISSISSIPPI
VALLEY AND EASTERN TEXAS. THIS COLD FRONT GENERALLY HAD AREAS OF
LIGHT TO MODERATE RAIN ALONG THE SOUTHERN PORTION. SOME WEAK
SOUTHERLY FLOW HAS DEVELOPED ACROSS THE GULF AHEAD OF THE BOUNDARY
WITH DEWPOINTS WARMING INTO THE UPPER 50S ACROSS SOUTHERN LA...WHILE
THE AIRMASS BEHIND THIS FRONT IS QUITE COOL AND DRY.
UPPER AIR DATA FROM 00 UTC AND VAPOR IMAGERY SHOWS A COMPLEX PATTERN
ACROSS THE CONUS. THE UPPER TROF DRIVING THE FRONTAL BOUNDARY
CONTINUES TO MOVE QUICKLY THROUGH THE UPPER MISSISSIPPI RIVER
VALLEY. THIS TROF HAS LEFT BEHIND A LOW...NOW CUT OFF...ACROSS THE
NORTHERN GULF OF CALIFORNIA. THE NEXT UPPER TROF...NOW MOVING ACROSS
THE SOUTHEASTERN GULF OF ALASKA AND INTO WESTERN BRITISH
COLUMBIA...WILL SERVE AS THE "KICKER" TO MOVE THE CUT OFF LOW
FURTHER EAST TOWARD THE GULF OF MEXICO AND LEAD TO SURFACE LOW
CYCLOGENESIS ALONG THE EVENTUAL STALLING COLD FRONTAL BOUNDARY.
&&
.SHORT TERM (TODAY THROUGH WEDNESDAY).
VERY CHALLENGING FORECAST THIS CYCLE AS THE MODELS ARE INDICATING A
VERY STRONG STORM SYSTEM HEADING OUR WAY BY TUESDAY AND WEDNESDAY.
AS INDICATED IN THE HEADLINE...THIS SYSTEM LOOKS TO PRESENT A
MULTIFACETED HAZARDOUS WEATHER THAT WILL INCLUDE NOT ONLY SEVERE
POTENTIAL...BUT HEAVY RAIN...COASTAL FLOODING AND MARINE HAZARDS.
FOR A SYSTEM THAT IS BETWEEN 48 AND 60 HOURS AWAY...THERE IS STILL
SOME SUBTLE DETAILS TO WORK OUT...BUT WHAT IS REMARKABLE IS THAT THE
MODELS ARE DOING A REASONABLY GOOD JOB WITH THE SYNOPTIC DETAILS AND
DELIVERING SOME RUN TO RUN CONSISTENCY.
RELATIVELY LITTLE DETAIL HAS BEEN PLACED ON THE FIRST 24 HOURS OF
THE FORECAST AS THE APPROACHING FRONT WILL HAVE LIMITED MOISTURE TO
WORK WITH AS WELL AS DIMINISHING SYNOPTIC FORCING...SO WILL
GENERALLY STAY CLOSE TO A BLEND OF THE MAV/MET GUIDANCE HERE AND THE
INHERITED NUMBERS.
BY TUESDAY AFTERNOON OUR FOCUS WILL SQUARELY SHIFT TO THE DEVELOPING
LOW THAT IS PROGGED TO OCCUR ON TUESDAY AFTERNOON OFF THE TEXAS
COAST AS THE CUT OFF LOW MOVES OUT OF THE TEXAS HILL COUNTRY AND
INTO THE COASTAL PLAIN. AS CYCLOGENESIS OCCURS ALONG THE STALLED
FRONTAL BOUNDARY...OUR WINDS WILL SHIFT TO EASTERLY AND BEGIN TO
SLOWLY STRENGTHEN.
AS WITH ALL STORM SYSTEMS...ITS THE DETAILS THAT DETERMINE HOW
EXTENSIVE THE THREAT WILL BE. THE 30/00Z GFS REMAINS THE STRONGEST
AND FASTER OF THE THREE MODELS EXAMINED. THE SOLUTION OFFERED BY THE
GFS SHOWS A LOW TRACK THAT ALLOWS OUR REGION TO GET INTO THE WARM
SECTOR FOR AT LEAST 12 HOURS AND WITH A STRENGTHENING SURFACE
LOW...INDUCE SUSTAINED SURFACE WINDS OVER THE NORTHERN GULF OF
MEXICO NEARING 45 KNOTS. THE 30/00Z EURO HAS TRENDED FROM ITS 29/12Z
RUN AS A COMPROMISE BETWEEN THE 29/12Z AND 30/00Z NAM CLOSER TO THE
GFS SOLUTION...IF NOT AS INTENSE. THE EURO STILL PLACES OUR REGION
WITHIN THE WARM SECTOR LONG ENOUGH TO POSE A SEVERE WEATHER THREAT.
THE SEVERE THREAT...OF ALL THE IMPACTS IS THE MOST UNCERTAIN. WHILE
THE KINEMATIC FIELDS ARE EXTREMELY IMPRESSIVE. IN FACT...0-6 KM
SHEAR VALUES EASILY EXCEEDS 60 KNOTS ACROSS A LARGE PORTION OF OUR
FORECAST AREA AS THE LOW NEARS. THE 0-1 KM SHEAR IS EQUALLY
IMPRESSIVE WITH VALUES EXCEEDING 30 KNOTS. THIS IS IN LARGE PART DUE
TO 950 MB WINDS PROGGED IN THE GFS TO BE NEAR 60 KNOTS ON WEDNESDAY
WITH 20 TO 25 KT SURFACE WINDS. WHILE THERE IS SOME SUSPICION THAT
THE GFS SOLUTION IS A LITTLE OVERDONE...SLIGHTLY LOWER VALUES IN THE
EURO STILL RESULT IN AN EXTREMELY FAVORABLE KINEMATIC ENVIRONMENT.
HOWEVER...AS IS ALWAYS THE CASE...WE NEED INSTABILITY. THE INITIAL
CONCERN IS THAT THE INITIAL AIRMASS WILL BE QUITE COOL AND
DRY...WITH ESSENTIALLY ZERO RETURN FLOW POTENTIAL UNTIL THE LOW IS
ALMOST HERE. THUS...INSTABILITY FORECASTS IN THE MODELS RANGE FROM
NEAR ZERO TO AS MUCH AS 1000 J/KG OF SBCAPE. IF THE MORE UNSTABLE
GFS SOLUTION VERIFIES IT IS GOING TO BE A VERY LONG DAY ON
WEDNESDAY. IN ANY EVENT...WITH SUCH FAVORABLE KINEMATICS IT WON'T
TAKE MUCH INSTABILITY TO CREATE SEVERE WEATHER. AND EVEN IF THIS
INSTABILITY IS ELEVATED (THIS IS VERY LIKELY DUE TO THE DYNAMICAL
COOLING INDICATED IN THE MODEL SOUNDINGS)...THE FACT THAT WINDS ARE
SO STRONG...JUST 1000 FT ABOVE THE SURFACE...THAT A DAMAGING WIND
THREAT COULD DEVELOP EVEN IF THESE WINDS ARE SOMEWHAT REDUCED BY
MIXING THROUGH A NEAR STABLE LAYER AT THE SURFACE AS A SQUALL LINE
MOVES THROUGH.
THE TIMING OF THIS THREAT APPEARS LIMITED TO COASTAL AREAS WEST OF
THE APALACHICOLA RIVER ON TUESDAY NIGHT AS A WARM FRONT PIVOTS
NORTHWARD YIELDING A DISCRETE SUPERCELLULAR THREAT. BY WEDNESDAY
MORNING THE SQUALL LINE SHOULD BE NEARING OUR WESTERN AREAS AND MOVE
THROUGH THE AREA THROUGHOUT THE DAY. THERE IS ENOUGH CONFIDENCE
BASED ON THE CLOSENESS OF THE GFS AND EURO SOLUTIONS TO SHOW 80 TO
90 PERCENT POPS ON WEDNESDAY.
NOW...FOR THE OTHER THREATS...
HEAVY RAINFALL...THE MODELS SHOW PWATS GOING TO NEAR 2 INCHES AHEAD
OF THIS SYSTEM. WITH SUCH STRONG SYNOPTIC FORCING ACROSS THE WESTERN
HALF OF THE REGION...WOULD NOT BE SURPRISED TO SEE 3 TO 6 INCH
WIDESPREAD AMOUNTS WITH SLIGHTLY HIGHER TOTALS DUE TO CONVECTIVE
ELEMENTS NEARING 8 INCHES MAINLY ALONG AND WEST OF A LINE FROM
ALBANY TO APALACHICOLA. EAST OF THIS AREA...WIDESPREAD 2 TO 4 INCHES
AMOUNTS WITH TOTALS UP TO 5 TO 6 INCHES WILL BE POSSIBLE. THIS COULD
EASILY LEAD TO URBANIZED...AND EVENTUALLY RIVER FLOODING.
COASTAL FLOODING...THIS IS A SIGNIFICANT CONCERN. EASTERLY WINDS ON
TUESDAY NIGHT WILL FOCUS HIGHER WATER LEVELS INTO FRANKLIN COUNTY
AND THE WESTERN PORTION OF APALACHEE BAY. AS THE WINDS BEGIN TO
SHIFT TO A MORE SOUTHERLY COMPONENT ON WEDNESDAY MORNING...WATER
WILL BEGIN TO PILE UP INTO THE BAY. WITH THE PASSAGE OF THE SQUALL
LINE...MODELS ARE SHOWING SURGE HEIGHTS PEAKING BETWEEN 3 AND 4
FEET...CENTERED ON AN AREA OF SAINT MARKS DOWN TO CEDAR KEY. THIS
WILL RESULT IN STORM TIDES NEARING 7 TO 8 FEET ABOVE MEAN LOWER LOW
WATER. THIS IS SIMILAR OR SLIGHTLY HIGHER IN MAGNITUDE TO LEVELS
SEEN DURING HURRICANE GUSTAV BACK IN 2007. GIVEN THAT THE
ASTRONOMICAL TIDE CHARTS FOR APALACHEE BAY SHOW VERY LITTLE TIDAL
DIFFERENCE BETWEEN THE HIGH AND LOW TIDES ON WEDNESDAY...THE CONCERN
FOR A PROLONGED PERIOD OF INUNDATION ALONG THE COASTAL AREAS FROM
FRANKLIN COUNTY EASTWARD TO DIXIE COUNTY IS QUITE HIGH. THUS...EVEN
THOUGH IT IS 48 TO 60 HOURS AWAY...WILL GO AHEAD AND ISSUE A COASTAL
FLOOD WATCH TO HIGHLIGHT THIS SIGNIFICANT FLOOD POTENTIAL LATER THIS
MORNING.
IN SUMMARY...A MULTIFACETED HAZARDOUS WEATHER EVENT IS LIKELY TO
IMPACT THE REGION BEGINNING TUESDAY NIGHT AND CONTINUING THROUGH
WEDNESDAY. HEAVY RAIN AND COASTAL FLOODING LOOK TO BE THE MOST
CERTAIN IMPACTS AT THIS TIME. SEVERE WEATHER POTENTIAL IS
INCREASED...THOUGH THERE REMAINS SOME UNCERTAINTY IN THE EVENTUAL
THERMODYNAMIC ENVIRONMENT ACROSS THE REGION ON WEDNESDAY. EVERYONE
IS URGED TO MONITOR THE LATEST FORECASTS...WATCHES AND WARNINGS FROM
THE NATIONAL WEATHER SERVICE ON THIS STORM SYSTEM.
.LONG TERM (WEDNESDAY NIGHT THROUGH SUNDAY).
EVEN THOUGH THERE IS LIKELY TO BE SOME INTERESTING WEATHER DURING
THE EXTENDED PORTION OF THE FCST...IT APPEARS AS THOUGH I DREW THE
LONG END OF THE STICK SO SPEAK...AS THE POTENTIAL HAZARDS IN THE
SHORT TERM (MAINLY TUE NIGHT AND WED) SHOULD FAR OUTWEIGH MOST OF
THE CONCERNS IN THE LONG TERM PERIOD...ESPECIALLY ONCE THE STRONG
COLD FRONT SWEEPS THROUGH THE REGION WED NIGHT AND THU MORNING.
ALTHOUGH WE WILL LIKELY STILL HAVE TO CARRY POPS IN THE FCST FOR WED
NIGHT AND WINDS MAY STILL BE NEAR GALE FORCE OVER THE WATERS...THE
SEVERE WX AND COASTAL FLOODING THREAT IS EXPECTED TO BE MOSTLY A
DAYTIME EVENT WHICH POSSIBLY COULD EXTEND INTO THE EARLY EVENING
HOURS ACROSS FAR EASTERN PORTIONS OF THE CWA.
THEREAFTER...ANTICIPATE A GENERALLY POP FREE FCST UNTIL SUN NIGHT OR
MON AT THE EARLIEST...AND ONLY IF THE 00 UTC SOLUTION OF THE GFS IS
CORRECT AND THE EARLIER 12 UTC EURO IS INCORRECT. HOWEVER
...ALTHOUGH IT IS STILL VERY EARLY IN THE BALL GAME...THERE IS A NEW
POTENTIAL PROBLEM THAT WE MAY HAVE TO DEAL WITH...AND THAT WILL BE
THE CONCERN FOR SOME VERY LOW TEMPERATURES BEHIND THIS STRONG COLD
FRONT ON FRIDAY AND ESPECIALLY SATURDAY MORNING (WHERE RADIATIONAL
COOLING CONDITIONS MAY BE NEAR IDEAL...DESPITE RISING 850 MB TEMPS).
I'M NOT SURE IF THIS HAS EVER HAPPENED BEFORE OVER PARTS OF THE
INTERIOR CWA...BUT SOME OF THE RAW MEX GRIDS WOULD ACTUALLY SKIP
RIGHT OVER A FREEZE...DIRECTLY TO A HARD FREEZE ON SATURDAY MORNING!
AM OBVIOUSLY NOT READY TO GO THIS FAR OUT ON A LIMB AT THIS TIME
FRAME...BUT A POSSIBLE LONG DURATION RADIATIONAL FREEZE IS APPEARING
MORE LIKELY FOR SATURDAY MORNING FOR A GOOD PORTION OF THE INTERIOR
...WITH AN ADVECTION FREEZE POSSIBLE FRIDAY MORNING FOR MUCH OF SE
AL AND THE NW CORNER OF SW GA. AFTER LOADING THE RAW GFS 40 MODEL
OUTPUT (WHICH LOOKS FAIRLY DECENT) WILL LIKELY USE A BLEND OF THIS
WITH THE MEX AND GRIDDED MOS AS A STARTING POINT. ALL INTERESTS ARE
URGED TO KEEP ABREAST OF THE LATEST FCSTS FROM THE NATIONAL WX
SERVICE...AS A CHANGE IN LOW TEMPS A FEW DEGREES IN EITHER DIRECTION
COULD HAVE SIGNIFICANT IMPACTS ON OUTDOOR PLANTS AND EVENT
PLANNING.
&&
.AVIATION...ALTHOUGH NOT AS VOLATILE AS IT EXPECTED TO BE FOR OUR
TAF LOCATIONS DURING THE MID WEEK PERIOD...THE NEXT 24 HRS COULD BE
A BIT INTERESTING WITH A FEW PERIODS OF SHOWERS AND MVFR CONDITIONS
AS MOSTLY MID-UPPER LEVEL CLOUDINESS (WITH A FEW POCKETS OF 3-4KFT
CIGS) PRECEDE THE APPROACH OF WEAK COLD FRONT FROM THE NORTHWEST
TONIGHT. BEFORE THE BULK OF THE CLOUDINESS ARRIVES...TLH AND VLD MAY
DROP TO MVFR LEVELS IF ALLOWED TO RADIATE FOR A COUPLE OF MORE HOURS
TONIGHT BEFORE CONDITIONS LIKELY IMPROVE THEREAFTER. ON MONDAY...
EXPECT THE BEST CHANCES FOR SHOWERS TO BE TO THE WEST IN THE MID TO
LATE AFTERNOON AS THE COLD FRONT GRADUALLY LOSES ITS PUNCH AS IT
PUSHES THROUGH THE REGION...WITH CLEARING SKIES AND VFR CONDITIONS
EXPECTED TO RETURN TO ALL LOCATIONS BY 06 UTC ON TUE.
&&
.MARINE...EXPECT TO SEE WINDS BEGIN TO INCREASE TONIGHT OUT OF THE
NORTH AS THE COLD FRONT MOVES THROUGH THE MARINE AREA. THERE IS SOME
CONCERN A BRIEF ADVISORY LEVEL WIND COULD BE OBSERVED...BUT FOR NOW
WILL FORECAST JUST CAUTIONARY CRITERIA. THE BIG STORY STARTS ON
TUESDAY AFTERNOON. WINDS WILL LIKELY BUILD THROUGH ADVISORY LEVEL TO
AT LEAST GALE FORCE GUSTS ON WEDNESDAY MORNING. SUSTAINED GALE FORCE
WINDS ARE POSSIBLE. USED THE LATEST RUN OF THE LOCAL SWAN MODEL TO
ARRIVE AT WAVE HEIGHTS THAT NEAR 18 FEET WELL OFFSHORE. NEEDLESS TO
SAY...SURF HEIGHTS AT THE COAST COULD BE VERY HIGH...POSSIBLY AS
HIGH AS 11 FEET FROM PANAMA CITY TO THE WESTERN PORTION OF SAINT
GEORGE ISLAND. OF COURSE...RIP CURRENT RISK WILL BE EXTREME DURING
THIS TIME AND EVERYONE IS STRONGLY ENCOURAGED TO REMAIN OUT OF THE
SURF. IT IS EXPECTED THAT HIGH SURF ADVISORIES OR WARNINGS WILL
BECOME NECESSARY BY TUESDAY MORNING.
&&
.FIRE WEATHER...CLOUDS...LOW LEVEL MOISTURE...AND RAIN CHANCES WILL
BE ON THE INCREASE FROM WEST TO EAST ACROSS THE CWA TODAY...SO DO
NOT EXPECT ANY FIRE WX CONCERNS. ALTHOUGH THERE IS EXPECTED TO BE A
BRIEF WINDOW OF DRIER AIR BEHIND THE WEAK COLD FRONT ON TUESDAY...IT
IS NOT EXPECTED TO BE DRY ENOUGH TO CAUSE ANY PROBLEMS. THEREAFTER
...WITH THE APPROACHING POTENTIAL VERY STRONG LOW PRESSURE SYSTEM
FOR THE MID WEEK PERIOD...RH'S SHOULD REMAIN WELL ABOVE CRITICAL
LEVELS UNTIL PERHAPS FRIDAY AT THE EARLIEST.
&&
.PRELIMINARY POINT TEMPS/POPS...
TALLAHASSEE 73 48 66 59 70 / 20 20 20 60 90
PANAMA CITY 73 50 65 61 71 / 30 20 30 80 90
DOTHAN 72 41 61 56 68 / 50 10 20 80 90
ALBANY 72 41 63 55 66 / 40 10 10 70 90
VALDOSTA 73 47 66 58 73 / 10 20 20 50 90
CROSS CITY 73 54 70 61 74 / 10 20 20 40 90
APALACHICOLA 72 53 65 63 70 / 20 20 30 70 90
&&
.TAE WATCHES/WARNINGS/ADVISORIES...
AL...NONE.
GA...NONE.
FL...COASTAL FLOOD WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY
MORNING FOR THE FOLLOWING ZONES: DIXIE...FRANKLIN...GULF...
JEFFERSON...TAYLOR...WAKULLA.
GM...SMALL CRAFT ADVISORY FROM 1 PM EST TUESDAY TO 1 AM EST
WEDNESDAY FROM DESTIN EASTWARD TO APALACHICOLA OUT TO 60
NAUTICAL MILES.
GALE WATCH FROM 1 AM EST WEDNESDAY UNTIL 1 AM EST THURSDAY
FROM DESTIN EASTWARD TO APALACHICOLA OUT TO 60 NAUTICAL MILES.
SMALL CRAFT ADVISORY FROM 7 PM EST TUESDAY TO 7 AM EST
WEDNESDAY FROM APALACHICOLA EASTWARD TO THE SUWANNEE
RIVER ENTRANCE OUT TO 60 NAUTICAL MILES.
GALE WATCH FROM 7 AM EST WEDNESDAY TO 1 AM EST THURSDAY FROM
APALACHICOLA EASTWARD TO THE SUWANNEE RIVER ENTRANCE OUT TO
60 NAUTICAL MILES.
&&
$$
LONG TERM/AVIATION/FIRE WEATHER...GOULD
REST OF DISCUSSION...GODSEY
