WATCHES: Severe Thunderstorm Watch Number 742

WWUS20 KWNS 211903
SEL2
SPC WW 211903
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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