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WWUS20 KWNS 030325

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 824

NWS STORM PREDICTION CENTER NORMAN OK

1025 PM CDT FRI SEP 2 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL AND EAST CENTRAL IOWA



EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 1025 PM

UNTIL 400 AM CDT.



HAIL TO 1 INCH 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 40

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 70 MILES WEST OF DES

MOINES IOWA TO 50 MILES EAST NORTHEAST OF CEDAR RAPIDS IOWA.  FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU4).



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...THERE WILL BE SOME RISK FOR THE CONVECTIVE CLUSTERS

MOVING INTO W CENTRAL/CENTRAL IA TO PERSIST FOR A FEW MORE

HOURS...WITH AN ATTENDANT RISK FOR DAMAGING WINDS.  THE ENVIRONMENT

IS SUPPORTIVE OF STRONG DOWNDRAFTS WITH STEEP MIDLEVEL LAPSE RATES

AND LARGE DCAPE/MODERATE CAPE...AS WELL AS EFFECTIVE BULK SHEAR

AROUND 35 KT TO MAINTAIN ORGANIZED CONVECTIVE STRUCTURES.  THE

UNCERTAINTY CENTERS ON INCREASING CONVECTIVE INHIBITION AND RATHER

MODEST FORCING FOR ASCENT ALONG THE WSW-ENE SURFACE FRONT IN IA.



AVIATION...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 550. MEAN STORM MOTION

VECTOR 26035.





...THOMPSON

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