

878 

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

