324 WWUS20 KWNS 221933 SEL1 SPC WW 221930 ILZ000-INZ000-MIZ000-230100- URGENT - IMMEDIATE BROADCAST REQUESTED SEVERE THUNDERSTORM WATCH NUMBER 521 STORM PREDICTION CENTER NORMAN OK 230 PM CDT MON JUL 22 2002 THE STORM PREDICTION CENTER HAS ISSUED A SEVERE THUNDERSTORM WATCH FOR PORTIONS OF NORTHERN AND CENTRAL ILLINOIS NORTHWESTERN INDIANA EXTREME SOUTHWEST LOWER MICHIGAN EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 230 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 ALONG AND 60 STATUTE MILES NORTH AND SOUTH OF A LINE FROM 40 MILES WEST NORTHWEST OF SPRINGFIELD ILLINOIS TO 55 MILES SOUTH SOUTHEAST OF SOUTH BEND INDIANA. 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. OTHER WATCH INFORMATION... CONTINUE...WW 520... DISCUSSION...DEEP CONVERGENCE ASSOCIATED WITH COLD FRONT EXTENDS FROM SWRN LOWER MI SWWD ACROSS THE SRN PORTIONS OF THE CHICAGO AREA INTO NORTHERN MO. AIR MASS IS EXTREMELY UNSTABLE AHEAD OF THIS FRONT...AND FRONT SHOULD INITIATE SEVERE THUNDERSTORMS AS IT MOVES SOUTHEASTWARD THROUGH THE EVENING. THOUGH SHEAR IS MARGINAL... LINEAR FORCING ASSOCIATED WITH FRONT AND EXTREME INSTABILITY WILL INCREASE THE THREAT OF WIND DAMAGE WITH THESE STORMS. 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 550. MEAN STORM MOTION VECTOR 26035. ...EVANS ;405,0902 414,0855 400,0855 391,0902;