Mike Wilhelm's Alabama Weather Blog

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Bamawx.com

   URGENT - IMMEDIATE BROADCAST REQUESTED
 TORNADO WATCH NUMBER 861
 NWS STORM PREDICTION CENTER NORMAN OK
 1145 AM CDT SUN AUG 24 2008

 THE NWS STORM PREDICTION CENTER HAS ISSUED A
 TORNADO WATCH FOR PORTIONS OF

        CENTRAL AND SOUTHERN ALABAMA
        SOUTHWESTERN AND EXTREME WEST-CENTRAL GEORGIA

 EFFECTIVE THIS SUNDAY MORNING AND EVENING FROM 1145 AM UNTIL 900
 PM CDT.

 TORNADOES...HAIL TO 0.5 INCH IN DIAMETER...THUNDERSTORM WIND
 GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
 AREAS.

 THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 75 STATUTE
 MILES EAST AND WEST OF A LINE FROM 20 MILES SOUTHEAST OF DOTHAN
 ALABAMA TO 15 MILES NORTH OF BIRMINGHAM ALABAMA.  FOR A COMPLETE
 DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE
 (WOUS64 KWNS WOU1).

 REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR
 TORNADOES AND SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
 AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
 THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
 AND POSSIBLE WARNINGS.

 DISCUSSION...DESPITE WEAKENING CENTRAL REGION...OUTER PORTIONS OF
 RESIDUAL TD FAY CIRCULATION CONTINUE TO SHOW FAVORABLE SHEAR FOR
 SUPERCELLS WITH ONLY GRADUAL WEAKENING OF WINDS JUST ABOVE GROUND
 LEVEL THROUGH AFTERNOON/EVENING...AND 0-1 KM SRH REMAINING IN
 200-400 J/KG OVER MUCH OF WW AREA.  CONVECTIVE COVERAGE FCST TO
 INCREASE IN VERY MOIST AND WEAKLY CAPPED AIR MASS...INCLUDING
 ADDITIONAL MINI-SUPERCELLS WITH INCREASING RISK OF A FEW TORNADOES.

 AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
 SURFACE AND ALOFT TO 0.5 INCH. EXTREME TURBULENCE AND SURFACE
 WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
 500. MEAN STORM MOTION VECTOR 16035.


 ...EDWARDS/HALES

   MESOSCALE DISCUSSION 2147
NWS STORM PREDICTION CENTER NORMAN OK
1011 AM CDT SUN AUG 24 2008

AREAS AFFECTED...PORTIONS AL...EXTREME SWRN GA.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 241511Z - 241715Z

BRIEF/SPORADIC SUPERCELLS MAY DEVELOP WITH OUTER BANDS REVOLVING
AROUND REMAINS OF TS FAY.  TORNADO POTENTIAL IS WEAK/MRGL ATTM BUT
MAY INCREASE THROUGH MID-LATE AFTERNOON.

SFC ANALYSIS SHOWS DIFFUSE LOW OVER SERN MS BETWEEN PIB-MEI...WITH
WEAK CENTRAL WINDS AND FILLING PRESSURE AS CIRCULATION OF FAY
CONTINUES TO WEAKEN.  LOW-MIDLEVEL REMAINS OF TS FAY HAVE BECOME
INTERMINGLED WITH PRE-EXISTING MID-UPPER LEVEL LOW THAT PIVOTED
SWD/SEWD ACROSS AR AND LA YESTERDAY AFTERNOON AND OVERNIGHT.
MOISTURE CHANNEL IMAGERY AND 12Z BMX/TLH RAOBS INDICATE PRONOUNCED
DRYING ALOFT FROM THAT UPPER PERTURBATION NOW WRAPPING AROUND ERN
PORTION OF COMBINED CIRCULATION.  STRONGEST DRYING APPEARS CLOSER TO
CENTER AS ALSO EVIDENT IN GPS PW DATA...WHICH SHOWS VALUES OF
1.7-1.8 INCH FROM MOUTH OF MS RIVER NEWD ACROSS MOB AREA THEN NWD
INTO CENTRAL AL...AND PRONOUNCED DROP IN PW LAST FEW HOURS BETWEEN
MOB-BHM.  RELATIVELY MOIST LOW LEVEL PLUME IS EVIDENT FARTHER E
ACROSS ERN AL...WRN GA AND FL PANHANDLE...WHICH SHOULD SUPPORT
CONVECTION POTENTIAL AS IT SHIFTS SLOWLY WWD IN STEP WITH
TRANSLATIONAL MOTION OF BROADER CIRCULATION.  WHILE DRY SLOT REDUCED
POTENTIAL CONVECTIVE COVERAGE CLOSER TO CENTER...IT IS SUPPORTING
CONSIDERABLE BREAKS IN CLOUDS ACROSS MUCH OF SRN/CENTRAL AL THAT
EXTEND EWD OVER BOUNDARY LAYER MOISTURE PLUME.  CONTINUED INSOLATION
IN BETWEEN EXISTING CONVECTIVE BANDS MAY OFFSET VERY WEAK MID-UPPER
LEVEL LAPSE RATES ENOUGH TO DEVELOP MLCAPE 250-500 J/KG OVER
PORTIONS CENTRAL AL DURING NEXT FEW HOURS...INCREASING TO 1000 J/KG
NEAR SRN PORTION AL/GA LINE.  STRENGTHENING INSTABILITY WILL
COINCIDE WITH WEAKENING OF LOW LEVEL SHEAR...A TREND ALREADY EVIDENT
IN DECREASE OF SELY NOCTURNAL LLJ FROM VWP SITES OVER SERN AND
CENTRAL AL.  HOWEVER...FCST SOUNDINGS SUGGEST HODOGRAPH SIZE STILL
WILL BE SUFFICIENT TO SUPPORT SUPERCELLS...ESPECIALLY FROM E-CENTRAL
AL NWWD ACROSS CENTRAL AL WHERE SFC FLOW IS MOST STRONGLY
BACKED...WITH 0-1 KM SRH 200-400 J/KG PERSISTING INTO AT LEAST
MID-AFTERNOON.

..EDWARDS.. 08/24/2008