Midwest Chasing

URGENT - IMMEDIATE BROADCAST REQUESTED
   SEVERE THUNDERSTORM WATCH NUMBER 640
   NWS STORM PREDICTION CENTER NORMAN OK
   1230 PM CDT THU AUG 23 2007

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

          NORTHERN AND CENTRAL ILLINOIS
          NORTHWEST INDIANA
          EXTREME SOUTHERN WISCONSIN
          LAKE MICHIGAN

   EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 1230 PM UNTIL
   800 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 90
   STATUTE MILES NORTH AND SOUTH OF A LINE FROM 10 MILES WEST
   SOUTHWEST OF MOLINE ILLINOIS TO 30 MILES EAST NORTHEAST OF MEIGS
   FIELD ILLINOIS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
   ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).

   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...CONVECTIVE SYSTEM MOVING EWD ACROSS ERN IA IS EXPECTED
   TO PROGRESS ENEWD AND INTENSIFY THIS AFTERNOON.  MCS IS IN ADVANCE
   OF A SHORT WAVE TROUGH MOVING INTO EXTREME WRN IA...AND IS EMBEDDED
   WITHIN A LARGELY UNIDIRECTIONAL WSWLY WIND FIELD WITH SPEEDS OF
   40-50 KT ABOVE THE PBL.  VISIBLE IMAGERY SHOWS MAINLY CLEAR SKIES
   OVER IL AND EXTREME SRN WI AHEAD OF THE MCS WHICH WILL ALLOW
   CONTINUED STRONG HEATING OF VERY MOIST AIR MASS.  DAMAGING WIND
   GUSTS AND OCCASIONAL HAIL WILL BE POSSIBLE WITH STRONGEST CELLS AS
   THEY MOVE ENEWD 35-40 KT.