

487 

WWUS20 KWNS 252055

SEL2

SPC WW 252055

ILZ000-INZ000-LMZ000-260200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 512

NWS STORM PREDICTION CENTER NORMAN OK

355 PM CDT THU JUN 25 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHEAST ILLINOIS

       NORTHWEST INDIANA

       LAKE MICHIGAN



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 355 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 45

STATUTE MILES EAST AND WEST OF A LINE FROM 30 MILES NORTHEAST OF

ROCKFORD ILLINOIS TO 80 MILES SOUTHEAST OF MARSEILLES ILLINOIS.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU2).



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 508...WW 509...WW

510...WW 511...



DISCUSSION...A VERY UNSTABLE AIR MASS HAS DEVELOPED ACROSS THIS

REGION THIS AFTERNOON WITH NO CAPPING.  DESPITE THE WEAK LOW LEVEL

FLOW/FOCUS... LAKE BREEZE AND OUTFLOW BOUNDARIES SHOULD FOCUS RAPID

THUNDERSTORM DEVELOPMENT THROUGH THE EVENING.  SHEAR REMAINS

SUPPORTIVE OF SUSTAINED/ORGANIZED SEVERE...INCLUDING BRIEF

SUPERCELLS...WITH PRIMARY THREATS OF LARGE HAIL AND DAMAGING WINDS.



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 32015.





...EVANS

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