April 19: Tornado Watch #2

URGENT - IMMEDIATE BROADCAST REQUESTED
   TORNADO WATCH NUMBER 155
   NWS STORM PREDICTION CENTER NORMAN OK
   220 PM CDT TUE APR 19 2011
   
   THE NWS STORM PREDICTION CENTER HAS ISSUED A
   TORNADO WATCH FOR PORTIONS OF 
   
          WESTERN ARKANSAS
          EASTERN OKLAHOMA
          NORTH-CENTRAL AND NORTHEAST TEXAS
   
   EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 220 PM UNTIL
   1000 PM CDT.
   
   TORNADOES...HAIL TO 4 INCHES IN DIAMETER...THUNDERSTORM WIND
   GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE
   AREAS.
   
   THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 85 STATUTE
   MILES EAST AND WEST OF A LINE FROM 15 MILES NORTH OF HARRISON
   ARKANSAS TO 60 MILES EAST SOUTHEAST OF DALLAS TEXAS.  FOR A
   COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
   UPDATE (WOUS64 KWNS WOU5).
   
   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.
   
   OTHER WATCH INFORMATION...CONTINUE...WW 154...
   
   DISCUSSION...EXPLOSIVE TSTM DEVELOPMENT IS EXPECTED ALONG COLD FRONT
   THIS AFTERNOON AS IT ENCOUNTERS A STRONGLY UNSTABLE AIR MASS WITH
   MLCAPE APPROACHING 3000-4500 J/KG.  DEEP-LAYER SHEAR VECTORS
   ORIENTED AT AN ANGLE TO THE FRONT IS SUGGESTIVE OF SUPERCELL
   EVOLUTION GIVEN THE DEGREE OF INSTABILITY AND 40-50 KT SWLY MIDLEVEL
   WIND FIELD.  VERY LARGE HAIL /I.E. GREATER THAN BASEBALL SIZE/ WILL
   BE POSSIBLE IN ADDITION TO A RISK OF A FEW TORNADOES GIVEN EFFECTIVE
   SRH VALUES OF 150-300 M2/S2.
   
   AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL
   SURFACE AND ALOFT TO 4 INCHES. EXTREME TURBULENCE AND SURFACE
   WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO
   600. MEAN STORM MOTION VECTOR 25030.