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URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 745

NWS STORM PREDICTION CENTER NORMAN OK

825 PM CDT SUN SEP 27 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       NORTHERN AND CENTRAL ILLINOIS

       NORTHWEST INDIANA

       SOUTHEAST WISCONSIN

       LAKE MICHIGAN



EFFECTIVE THIS SUNDAY NIGHT AND MONDAY MORNING FROM 825 PM UNTIL

200 AM CDT.



TORNADOES...HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS

TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 60 STATUTE

MILES EAST AND WEST OF A LINE FROM 30 MILES NORTH OF MILWAUKEE

WISCONSIN TO 35 MILES SOUTH OF DECATUR ILLINOIS.  FOR A COMPLETE

DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE

(WOUS64 KWNS WOU5).



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.



DISCUSSION...TSTMS EXPECTED TO INCREASE ALONG COLD FRONT AND ALONG

PRE-FRONTAL CONFLUENCE AXIS OVER SRN WI/IL...AHEAD OF STRONG/

AMPLIFYING SHORTWAVE TROUGH NOW OVER SE MN.  ALTHOUGH THE

PRE-FRONTAL ACTIVITY LIKELY WILL REMAIN SLIGHTLY ELEVATED...

AND...WITH TIME...LINEAR FORCING FOR ASCENT WILL INCREASE ALONG COLD

FRONT...FOR THE NEXT FEW HOURS A QUASI-DISCRETE STORM MODE IS

EXPECTED TO PREVAIL.  GIVEN MAGNITUDE OF DEEP SHEAR /AOA 60

KTS/...SUPERCELL STRUCTURES LIKELY WILL BE ASSUMED BY ANY SUSTAINED

UPDRAFTS.  INFLUX OF SOMEWHAT MORE SUBSTANTIAL MOISTURE NOW NEAR STL

INTO CNTRL/NRN IL STORMS LATER TONIGHT FURTHER SUGGESTS POSSIBLE

TORNADOES GIVEN FACT THAT FLOW IMMEDIATELY AHEAD OF FRONT SHOULD

MAINTAIN A SIZABLE SLY COMPONENT BENEATH 50+ KT WLY 700 MB FLOW.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND

GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 350.

MEAN STORM MOTION VECTOR 26050.





...CORFIDI

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