SEVERE THUNDERSTORM WATCH NUMBER 121

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.