River Flood Warning 50, NWS Tallahassee, FL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
948 PM EST THU MAR 11 2010

.DISCUSSION...01 UTC SURFACE ANALYSIS SHOWS A 998 MB SURFACE LOW
ABOUT NEAR DES MOINES WITH A COLD FRONT EXTENDING DOWN THE MID AND
SOUTHERN MISSISSIPPI RIVER VALLEY. DEWPOINT ANALYSIS SHOWS THE 60
DEGREE LINE JUST NORTH OF OUR FORECAST AREA WITH DEWPOINTS GENERALLY
IN THE LOWER 60S ACROSS NORTH FLORIDA WITH MID 60S JUST OFFSHORE.
SURFACE DATA SHOW VERY WEAK ONSHORE FLOW AHEAD OF THE COLD FRONT
ACROSS LOUISIANA.

UPPER AIR DATA FROM 00 UTC SHOWS AN IMPRESSIVE 175KT 250 MB JET
MOVING ACROSS THE NORTHWESTERN GULF OF MEXICO. EVEN THE SOUNDING
FROM KTAE AT 250 MB SHOWED A WIND OF 153 KT WITH THE PEAK WIND IN
THE SOUNDING (164 KT) REPORTED AT 200 MB. VAPOR IMAGERY AND 500 MB
DATA SHOW A LOW RIGHT ON TOP OF THE SURFACE FEATURE ACROSS IOWA WITH
THE SECONDARY SOUTHERN STREAM IMPULSE MOVING INTO THE ARKLATEX. IT
IS THIS SECONDARY IMPULSE THAT SHOULD GET THINGS GOING ACROSS THE
WESTERN GULF COAST STATES TONIGHT.

THE KTAE SOUNDING SHOWS A RELATIVELY DRY LAYER FROM 900 MB ON UP TO
600 MB. LOW LEVEL WARM ADVECTION OVER THE LAST 24 HOURS HAS INDUCED
A CAPPING INVERSION AT 900 MB. LAPSE RATES IN THE 700-500 MB LAYER
ARE ACTUALLY PRETTY GOOD AND WITH SOME DYNAMICAL COOLING EXPECTED AS
THE UPPER IMPULSE APPROACHES...THIS LAYER WILL BECOME INCREASINGLY
MORE FAVORABLE FOR CONVECTION.

FOR THE IMMEDIATE SHORT TERM OF THE FORECAST...VERY LITTLE IS
EXPECTED TO HAPPEN TONIGHT. LOWER AND MID LEVEL DRY AIR WILL HELP
LIMIT THE OVERALL COVERAGE OF PRECIPITATION AND KEEP IT ON THE LIGHT
SIDE. OVER TIME...AS THE LOW LEVELS MOISTEN...PRECIPITATION SHOULD
BECOME MORE WIDESPREAD...BUT MODEL SOUNDINGS TEND TO AGREE THAT THIS
WON'T HAPPEN UNTIL CLOSER TO DAYBREAK.

AFTER SUNRISE THERE IS SOME CONCERN AS TO HOW THE CONVECTION WILL
UNFOLD. THE 11/09Z WRF WAS SHOWING VERY LITTLE ACTIVITY IN THE
AFTERNOON...MAINLY JUST CONFINED TO THE FRONTAL BOUNDARY. THE 11/21Z
WRF HOWEVER SHOWS MUCH MORE WIDESPREAD COVERAGE WITH EVEN SOME
DECENT CONVECTIVE ELEMENTS PRESENT IN THE SIMULATED REFLECTIVITY BY
AFTERNOON. THIS ALSO SEEMS TO BE CLOSER TO THE 11/18Z NAM.

AS FAR AS SEVERE CHANCES GO...0-6 KM SHEAR VALUES APPROACH 50-55 KTS
BY MID MORNING ACROSS THE REGION...ESPECIALLY ACROSS THE NORTHERN
HALF OF THE FORECAST AREA. THE SHEAR PROFILE BECOMES MORE
UNIDIRECTIONAL AS THE COLD FRONT NEARS...WITH THE BULK OF THE FASTER
FLOW IN THE 3-6 KM LAYER. THUS...THE OVERALL TORNADO POTENTIAL
SEEMS RELATIVELY LOW. HOWEVER...THERMODYNAMICALLY...THE MODELS ARE
LATCHING ON TO SOME BETTER INSTABILITY IN THE LAST COUPLE OF CYCLES.
THE GFS HAS BETTER INSTABILITY THAN ANY OF THE MODELS...MUCAPES IN
THE 1000-1500 J/KG RANGE PRIMARILY IN SOUTHWEST GEORGIA. SREF DATA
DOES SHOW DECENT (30-50 PERCENT) PROBABILITIES OF THESE HIGHER
MUCAPE VALUES...SO THERE IS SOME SUPPORT OUTSIDE THE GFS FOR THESE
VALUES. THE REMAINING CONCERN WILL BE HOW MUCH OF A STABILIZING
IMPACT THE MARINE LAYER WILL HAVE ON CONVECTION. THIS IMPACT IS
ILLUSTRATED WELL IN THE LOCALLY RUN SEVERE PROBABILITIES WHICH SHOW
15% OR HIGHER SVR PROBS NORTH OF THE FLORIDA BORDER. GIVEN BETTER
INSTABILITY PROFILES (AND LOWER FREEZING LEVELS) PRIMARY THREAT WILL
BE LARGE HAIL WITH A DAMAGING WIND THREAT DEVELOPING PARTICULARLY IF
ANY CONVECTIVE ELEMENTS CAN ORGANIZE INTO LINEAR SEGMENTS ALONG OR
JUST AHEAD OF THE FRONTAL BOUNDARY. AN ISOLATED TORNADO CANNOT BE
RULED OUT WITH SUFFICIENT DEEP LAYER SHEAR FOR ROTATING
UPDRAFTS...BUT IT APPEARS TO BE MORE OF A SECONDARY THREAT AT THIS
TIME.

BASED ON THE LAST COUPLE OF MODEL RUNS WILL GO AHEAD AND PLACE SOME
T+ WORDING IN THE GRIDS...BUT ONLY IN THE HIGHER CONFIDENCE AREAS OF
SOUTH GEORGIA WHERE IT LOOKS LIKE THE COMBINATION OF SHEAR AND
BETTER INSTABILITY WILL OVERLAP. WILL KEEP MENTION OF GUSTY WINDS
ELSEWHERE. THE FLOOD WATCH WILL BE KEPT IN PLACE FOR NOW ACROSS THE
HEAVILY RAINED ON AREAS OF NORTH FLORIDA AS A COUPLE OF MODELS DO
SHOW THE POTENTIAL OF ANOTHER QUICK 1-2 INCHES WITH HIGHER AMOUNTS
POSSIBLE IN THE HEAVIER STORMS.

WILL BE MAKING A FEW OTHER MINOR TWEAKS TO THE CURRENT GRIDS...BUT
NO OTHER SIGNIFICANT CHANGES PLANNED AT THIS TIME. HAVE A GREAT
NIGHT!

&&

AVIATION...CONDITIONS HAVE BRIEFLY IMPROVED TO VFR...EXCEPT FOR
LINGERING PATCHES OF IFR CEILINGS OVER SOUTH CENTRAL GEORGIA AND THE
EASTERN FLORIDA BIG BEND. HOWEVER...THE COMBINATION OF A VERY MOIST
AIRMASS AT LOW LEVELS...LIGHT SURFACE WINDS...AND A THINNING CLOUD
COVER WILL RESULT IN A RETURN TO MVFR TO IFR CONDITIONS ACROSS THE
AREA LATER TONIGHT THROUGH FRIDAY MORNING. CEILINGS WILL LOWER TO
IFR AFTER MIDNIGHT. VISIBILITIES WILL BECOME MVFR ACROSS SOUTHEAST
ALABAMA AND THE FLORIDA PANHANDLE...AND IFR IN FOG ACROSS SOUTHWEST
AND SOUTH CENTRAL GEORGIA AND THE FLORIDA BIG BEND. A FRONTAL
BOUNDARY...CURRENTLY EXTENDING WEST TO EAST OFFSHORE ACROSS THE
NORTHEAST GULF...WILL BEGIN TO RETURN NORTHWARD LATER TONIGHT...
SPREADING ADDITIONAL RAIN BACK OVER THE FLORIDA PANHANDLE...AND THEN
NORTHEAST ACROSS THE REST OF THE AREA FRIDAY MORNING. A SQUALL LINE
IS EXPECTED TO DEVELOP TO THE WEST OF THE AREA...IN ADVANCE OF AN
APPROACHING COLD FRONT ON FRIDAY...AND SWEEP EASTWARD ACROSS THE
TRI-STATE AREA FRIDAY AFTERNOON AND THROUGH EARLY FRIDAY NIGHT.
THERE IS THE POTENTIAL FOR A FEW THUNDERSTORMS ASSOCIATED WITH THIS
SQUALL LINE TO PRODUCE DAMAGING WIND GUSTS AND HAIL.

&&

.MARINE...WILL SEE CONDITIONS BELOW HEADLINE CRITERIA THIS EVENING
AND TOMORROW...BUT WILL LIKELY SEE A PERIOD OF ADVISORY CONDITIONS
THIS WEEKEND IN STRONG WESTERLY FLOW.

&&

.TAE WATCHES/WARNINGS/ADVISORIES...

AL...NONE.
GA...NONE.
FL...FLOOD WATCH THROUGH EARLY SATURDAY MORNING ALL ZONES.
GM...NONE.

&&

AVIATION...DUVAL
REST OF DISCUSSION...GODSEY

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE TALLAHASSEE FL
1004 PM EST THU MAR 11 2010

ALZ065>069-FLZ007>019-026>029-034-GAZ120>131-142>148-155>161-
GMZ730-750-755-765-770-775-120900-
COFFEE-DALE-HENRY-GENEVA-HOUSTON-INLAND WALTON-COASTAL WALTON-
HOLMES-WASHINGTON-JACKSON-BAY-CALHOUN-GULF-FRANKLIN-GADSDEN-LEON-
JEFFERSON-MADISON-LIBERTY-WAKULLA-TAYLOR-LAFAYETTE-DIXIE-QUITMAN-
CLAY-RANDOLPH-TERRELL-DOUGHERTY-LEE-WORTH-TURNER-TIFT-BEN HILL-
IRWIN-EARLY-MILLER-BAKER-MITCHELL-COLQUITT-COOK-BERRIEN-SEMINOLE-
DECATUR-GRADY-THOMAS-BROOKS-LOWNDES-LANIER-
APALACHEE BAY OR COASTAL WATERS FROM KEATON BEACH TO OCHLOCKONEE
RIVER FL OUT TO 20 NM-
COASTAL WATERS FROM APALACHICOLA TO DESTIN FL OUT 20 NM-
COASTAL WATERS FROM  OCHLOCKONEE RIVER TO APALACHICOLA FL OUT TO
20 NM-
COASTAL WATERS FROM  SUWANNEE RIVER TO KEATON BEACH OUT 20 NM-
WATERS FROM APALACHICOLA TO DESTIN FL FROM 20 TO 60 NM-
WATERS FROM  SUWANNEE RIVER TO APALACHICOLA FL FROM 20 TO 60 NM-
1004 PM EST THU MAR 11 2010 /904 PM CST THU MAR 11 2010/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTHEAST ALABAMA...
SOUTHWEST AND SOUTH CENTRAL GEORGIA...AND THE FLORIDA BIG BEND AND
PANHANDLE...AND ADJACENT COASTAL WATERS.

...SLIGHT RISK OF SEVERE STORMS ACROSS MUCH OF THE REGION
ON FRIDAY...

.DAY ONE...TONIGHT...
THE REGION WILL BE IN BETWEEN SYSTEMS TONIGHT WITH A COLD FRONT
LOCATED TO THE WEST OF THE REGION. AS THIS COLD FRONT MOVES EASTWARD
OVERNIGHT AND THE ATMOSPHERE ONCE AGAIN MOISTENS...SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS WILL BEGIN TO DEVELOP ACROSS THE EASTERN
FLORIDA PANHANDLE AND SOUTHEAST ALABAMA. THESE STORMS ARE EXPECTED
TO REMAIN BELOW SEVERE LIMITS BEFORE DAYBREAK.

.DAYS TWO THROUGH SEVEN...FRIDAY THROUGH WEDNESDAY...
A COLD FRONT WILL MOVE EAST ACROSS THE FORECAST AREA ON FRIDAY
AND COMBINE WITH AN UPPER LEVEL DISTURBANCE TO GENERATE SHOWERS AND
THUNDERSTORMS. DUE TO INCREASING WIND SHEAR AND AN UNSTABLE AIRMASS
ACROSS THE REGION...SOME OF THESE STORMS COULD BECOME STRONG TO
SEVERE ACROSS SOUTHEAST ALABAMA AND THE EASTERN FLORIDA PANHANDLE IN
THE MORNING. THE THREAT FOR SEVERE STORMS MAY INCREASE AS THE LINE
MOVES EASTWARD IN THE AFTERNOON INTO SOUTHWEST AND SOUTH CENTRAL
GEORGIA WHERE GREATER INSTABILITY IS PREDICTED TO BE IN PLACE. THE
MAIN THREAT WITH THESE STORMS WILL BE THE POTENTIAL FOR LARGE HAIL
AND POSSIBLY DAMAGING WINDS IF THESE STORMS CAN ORGANIZE INTO
INDIVIDUAL LINES. THE TORNADO THREAT REMAINS LOW.

DRIER AND COOLER CONDITIONS ARE ON TAP FOR THE UPCOMING WEEKEND AND
EARLY PORTION OF NEXT WEEK. DESPITE THE COOLER CONDITIONS...WE ARE
NOT EXPECTING ANY SUB-FREEZING TEMPERATURES AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION MAY BE NEEDED ON FRIDAY.

FOR ADDITIONAL INFORMATION...VISIT THE NATIONAL WEATHER SERVICE
WEBSITE ON THE INTERNET AT WEATHER.GOV...THEN CLICK ON YOUR AREA
OF INTEREST ON THE NATIONAL MAP.

GODSEY