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743 

WWUS20 KWNS 311750

SEL1

SPC WW 311750

ALZ000-GAZ000-MSZ000-TNZ000-010200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 121

NWS STORM PREDICTION CENTER NORMAN OK

1250 PM CDT SAT MAR 31 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHERN ALABAMA

       NORTHWEST GEORGIA

       NORTHEAST MISSISSIPPI

       WESTERN AND MIDDLE TENNESSEE



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 1250 PM UNTIL

900 PM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 45 MILES WEST

SOUTHWEST OF JACKSON TENNESSEE TO 40 MILES NORTHEAST OF

CHATTANOOGA TENNESSEE.  FOR A COMPLETE DEPICTION OF THE WATCH SEE

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR 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. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.



DISCUSSION...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND

INTENSITY THIS AFTERNOON AHEAD OF A WEAK COLD FRONT SETTLING SWD

THROUGH TN.  ABUNDANT SUNSHINE COUPLED WITH BOUNDARY LAYER DEWPOINTS

IN THE 60S AND VERY STEEP MIDLEVEL LAPSE RATES HAVE YIELDED A

MODERATELY UNSTABLE AIR MASS AS OF EARLY AFTERNOON WHERE MLCAPE HAS

INCREASED TO 2500 J/KG.  WHILE VERTICAL SHEAR WILL REMAIN MARGINALLY

SUPPORTIVE FOR ORGANIZED STORM MODES...THE STEEP LAPSE RATES AND

MODERATE TO POTENTIALLY STRONG INSTABILITY WILL COMPENSATE.  LARGE

HAIL APPEARS TO BE THE PRIMARY HAZARD...THOUGH THE RISK FOR DAMAGING

WINDS WILL INCREASE AS STORMS DEVELOP COLD POOLS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 31020.





...MEAD

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