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WWUS20 KWNS 211903

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ARZ000-KSZ000-MOZ000-OKZ000-TXZ000-220300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 742

NWS STORM PREDICTION CENTER NORMAN OK

200 PM CDT MON SEP 21 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EXTREME NORTHWEST ARKANSAS

       SOUTHEAST KANSAS

       SOUTHWEST AND CENTRAL MISSOURI

       CENTRAL AND EASTERN OKLAHOMA

       EXTREME NORTHWEST TEXAS



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 200 PM UNTIL

1000 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 75

STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES NORTH

NORTHWEST OF SPRINGFIELD MISSOURI TO 40 MILES SOUTH SOUTHEAST OF

WICHITA FALLS TEXAS.  FOR A COMPLETE DEPICTION OF THE WATCH SEE

THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).



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...THUNDERSTORMS WILL GRADUALLY INCREASE IN

COVERAGE/INTENSITY ACROSS MO/SE KS AND OK THIS AFTERNOON AS THE LOW

LEVELS CONTINUE TO DESTABILIZE IN ADVANCE OF A COLD FRONT AND

PRE-FRONTAL TROUGH.  DEEP LAYER VERTICAL SHEAR IS SOMEWHAT MARGINAL

FOR SUPERCELLS IN THE WARM SECTOR...WHILE MLCAPE VALUES RANGE FROM

2000-3000 J/KG BASED ON SURFACE TEMPERATURES IN THE 80S WITH

BOUNDARY LAYER DEWPOINTS OF 68-70 F.  IT APPEARS THAT LARGE HAIL AND

DAMAGING WINDS WILL BE THE MAIN SEVERE THREATS THIS AFTERNOON.  THE

SEVERE THREAT WILL CONTINUE INTO THIS EVENING AND EARLY TONIGHT AS

STORMS GRADUALLY EVOLVE INTO AN EXTENSIVE BAND ALONG THE FRONT AND

SPREAD EWD/SEWD.



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 26025.





...THOMPSON

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