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WWUS20 KWNS 302259

SEL7

SPC WW 302259

ARZ000-OKZ000-TXZ000-010700-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 257

NWS STORM PREDICTION CENTER NORMAN OK

555 PM CDT SAT APR 30 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       SOUTHWEST ARKANSAS

       SOUTHEAST OKLAHOMA

       NORTHEAST TEXAS



EFFECTIVE THIS SATURDAY AFTERNOON AND SUNDAY MORNING FROM 555 PM

UNTIL 200 AM CDT.



TORNADOES...HAIL TO 2.5 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 70 STATUTE

MILES EAST AND WEST OF A LINE FROM 10 MILES SOUTHWEST OF TYLER

TEXAS TO 25 MILES NORTH NORTHWEST OF DE QUEEN ARKANSAS.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU7).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



DISCUSSION...INCIPIENT STORM DEVELOPMENT IS UNDERWAY ALONG COLD

FRONT OVER THE DALLAS-FT. WORTH AREA WITHIN A STRONGLY UNSTABLE AIR

MASS WITH MLCAPE VALUES OF 3000 J/KG. KINEMATIC ENVIRONMENT INVOF

COLD FRONT IS CHARACTERIZED BY A WEAK LOW-LEVEL WIND FIELD BUT 40-50

KT EFFECTIVE BULK SHEAR.  HOWEVER...AS STORMS MATURE...THEY WILL

ENCOUNTER STRONGER LOW-LEVEL SHEAR AND HIGHER BOUNDARY LAYER

MOISTURE CONTENT WITH EWD EXTENT.  AS SUCH...INITIAL HAZARDS WILL BE

LARGE HAIL AND LOCALLY DAMAGING WINDS WITH AN INCREASED TORNADO

THREAT AFTER 01/00Z.



AVIATION...TORNADOES AND A FEW SEVERE THUNDERSTORMS WITH HAIL

SURFACE AND ALOFT TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE

WIND GUSTS TO 60 KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO

500. MEAN STORM MOTION VECTOR 24030.





...MEAD

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