April 15: Tornado Watch #3

URGENT - IMMEDIATE BROADCAST REQUESTED
   TORNADO WATCH NUMBER 142
   NWS STORM PREDICTION CENTER NORMAN OK
   1250 PM CDT FRI APR 15 2011
   
   THE NWS STORM PREDICTION CENTER HAS ISSUED A
   TORNADO WATCH FOR PORTIONS OF 
   
          WESTERN AND SOUTHERN ILLINOIS
          WESTERN KENTUCKY
          EASTERN MISSOURI
   
   EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 1250 PM UNTIL
   900 PM CDT.
   
   TORNADOES...HAIL TO 2 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 45 MILES SOUTH SOUTHWEST OF
   PADUCAH KENTUCKY TO 70 MILES NORTH NORTHWEST OF ALTON ILLINOIS. 
   FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
   OUTLINE UPDATE (WOUS64 KWNS WOU2).
   
   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 140...WW 141...
   
   DISCUSSION...TSTMS ARE EXPECTED TO DEVELOP THIS AFTERNOON ALONG COLD
   FRONT AND WITHIN DRY SLOT OF INTENSE MID TO UPPER-LEVEL CYCLONE. 
   DAYTIME HEATING...BOUNDARY LAYER DEWPOINTS IN THE 50S AND 500 MB
   TEMPERATURES OF AROUND -20 C WILL RESULT IN A STEEP LAPSE RATE
   ENVIRONMENT WITH MLCAPE VALUES APPROACHING 1000-1500 J/KG.  WHEN
   COUPLED WITH A VERTICALLY VEERING WIND PROFILE...SETUP WILL FAVOR
   THE DEVELOPMENT OF SUPERCELLS CAPABLE OF TORNADOES AND LARGE HAIL.
   
   AVIATION...TORNADOES AND 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
   350. MEAN STORM MOTION VECTOR 21035.