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000 

WWUS20 KWNS 252000

SEL9

SPC WW 252000

ILZ000-INZ000-MIZ000-LEZ000-LHZ000-LMZ000-260300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 689

NWS STORM PREDICTION CENTER NORMAN OK

300 PM CDT TUE SEP 25 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       PARTS OF NORTHEAST ILLINOIS

       PARTS OF NORTHERN INDIANA

       MUCH OF SOUTHERN MICHIGAN

       LAKE ERIE

       LAKE HURON

       LAKE MICHIGAN



EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 300 PM UNTIL

1000 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 85

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES SOUTH

SOUTHWEST OF MEIGS FIELD ILLINOIS TO 30 MILES EAST NORTHEAST OF

BAD AXE MICHIGAN.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).



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...THUNDERSTORMS ARE INCREASING IN BOTH NUMBER AND

INTENSITY ACROSS NERN IL AHEAD OF COLD FRONT AND S/WV TROUGH. AIR

MASS EWD ACROSS LWR MI HAD BECOME MDTLY UNSTABLE WITH 30-40 KT OF

DEEP LAYER SHEAR.  STORM MODE WILL EVOLVE INTO LINE SEGMENTS AND BOW

AS THEY CONTINUE E/NEWD ACROSS THE WATCH WITH INCREASING WIND DAMAGE

POTENTIAL.



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 24035.





...HALES

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