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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 821

NWS STORM PREDICTION CENTER NORMAN OK

350 AM CDT FRI SEP 2 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHERN IOWA

       SOUTH CENTRAL AND SOUTHEASTERN MINNESOTA

       SOUTHWEST WISCONSIN



EFFECTIVE THIS FRIDAY MORNING FROM 350 AM UNTIL 1100 AM CDT.



HAIL TO 1.5 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 EITHER SIDE OF A LINE FROM 10 MILES SOUTH SOUTHWEST

OF SPENCER IOWA TO 45 MILES EAST SOUTHEAST OF LA CROSSE

WISCONSIN.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



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...CLUSTER OF TSTMS THAT HAS FORMED/STRENGTHENED OVER NW

IA IN THE PAST HOUR LIKELY IS ROOTED AROUND 800 MB...ABOVE SHALLOW

POST-COLD FRONTAL INVERSION.  NEVERTHELESS...GIVEN FACT THAT CLUSTER

IS EMBEDDED IN 35 KT MEAN...DEEP...UNIDIRECTIONAL WSW FLOW...AND

WILL HAVE ACCESS TO INCREASINGLY RICH MOISTURE WITH EWD EXTENT /PW

AOA 1.50 IN/...SETUP COULD SUPPORT SMALL BOWING SEGMENTS WITH HIGH

WIND.  THE STORMS SHOULD CONTINUE TO MOVE/DEVELOP E/ENE ACROSS NRN

IA AND PERHAPS SRN MN/SW WI ALONG ZONE OF INCREASING

FRONTOGENESIS/ASCENT ON S SIDE OF ND UPR IMPULSE.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 26030.





...CORFIDI

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