WATCHES: Severe Thunderstorm Watch Number 648

WWUS20 KWNS 252205
SEL8
SPC WW 252205
ILZ000-INZ000-MOZ000-260400-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 648
NWS STORM PREDICTION CENTER NORMAN OK
505 PM CDT TUE SEP 25 2012

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

SOUTHERN ILLINOIS
EXTREME SOUTHWEST INDIANA
EAST CENTRAL MISSOURI

EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 505 PM UNTIL
1100 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 35
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 60 MILES WEST
SOUTHWEST OF SAINT LOUIS MISSOURI TO 25 MILES EAST NORTHEAST OF
EVANSVILLE INDIANA. FOR A COMPLETE DEPICTION OF THE WATCH SEE
THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU8).

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...A BROKEN BAND OF SEVERE STORMS WILL LIKELY PERSIST
ALONG A SURFACE FRONT FROM E CENTRAL IL EWD ACROSS SRN IL/SW INDIANA
THROUGH THIS EVENING. A FEED OF STEEP MIDLEVEL LAPSE RATES AND
MLCAPE NEAR 2000 J/KG WILL MAINTAIN STRONG UPDRAFTS AND THE
POTENTIAL FOR BOTH LARGE HAIL AND DAMAGING OUTFLOW WINDS.
ADDITIONALLY...DEEP-LAYER VERTICAL SHEAR IS SUFFICIENT FOR ORGANIZED
MULTICELL CLUSTERS AND SOME SUPERCELL STRUCTURES...WHICH MAY LOCALLY
ENHANCE THE RISK FOR LARGE HAIL.

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 550. MEAN STORM
MOTION VECTOR 29020.


...THOMPSON

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