WATCHES: Severe Thunderstorm Watch Number 509

WWUS20 KWNS 251749
SEL9
SPC WW 251749
IAZ000-ILZ000-WIZ000-260000-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 509
NWS STORM PREDICTION CENTER NORMAN OK
1250 PM CDT THU JUN 25 2009

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

EASTERN IOWA
NORTHWEST ILLINOIS
EXTREME SOUTHWEST WISCONSIN

EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 1250 PM UNTIL
700 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 70
STATUTE MILES EAST AND WEST OF A LINE FROM 35 MILES NORTHWEST OF
DUBUQUE IOWA TO 25 MILES SOUTH OF PEORIA ILLINOIS. 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.

OTHER WATCH INFORMATION...CONTINUE...WW 508...

DISCUSSION...THUNDERSTORMS EXPECTED TO CONTINUE INCREASING IN
COVERAGE AND INTENSITY GIVEN VERY UNSTABLE AIR MASS AS AREA IS
SKIRTED BY LARGE SCALE ASCENT ASSOCIATED WITH GREAT LAKES UPPER
TROUGH. LOW LEVEL SHEAR/FLOW IS WEAK...THOUGH UPPER LEVEL NWLY
WINDS SHOULD ENHANCE THE POTENTIAL FOR A FEW SEVERE
STORMS...INCLUDING ORGANIZATION INTO CLUSTERS/LINES. LARGE HAIL AND
DAMAGING WINDS WILL BE PRIMARY SEVERE THREATS AS STORMS PERSIST INTO
THE EVENING.

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 32015.

...EVANS

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