WATCHES: Severe Thunderstorm Watch Number 824

WWUS20 KWNS 030325
SEL4
SPC WW 030325
IAZ000-030900-

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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