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335 

WWUS20 KWNS 120818

SEL7

SPC WW 120818

TXZ000-121500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 287

NWS STORM PREDICTION CENTER NORMAN OK

315 AM CDT THU MAY 12 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHWEST TEXAS



EFFECTIVE THIS THURSDAY MORNING FROM 315 AM UNTIL 1000 AM CDT.



HAIL TO 2.5 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 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 30 MILES WEST OF DEL

RIO TEXAS TO 25 MILES EAST SOUTHEAST OF HONDO TEXAS.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU7).



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...TSTM INITIATION IS UNDERWAY ALONG W-E ORIENTED OUTFLOW

BOUNDARY NW OF DRT.  GLANCING INFLUENCE OF MIDLEVEL VORTICITY

MAXIMUM PASSING TO THE N OF AREA COUPLED WITH LOW-LEVEL WAA APPEAR

TO BE THE PRIMARY MECHANISMS FORCING THIS ACTIVITY.  LOCAL

ENVIRONMENT FEATURES VERTICALLY VEERING WIND PROFILES WITH 50 KT OF

DEEP-LAYER SHEAR AND MUCAPE OF 2000-4000 J/KG.  AS SUCH...SETUP WILL

FAVOR THE DEVELOPMENT OF SUPERCELLS CAPABLE OF LARGE HAIL AND

LOCALLY DAMAGING WINDS.  AN ISOLATED TORNADO WILL BE

POSSIBLE...THOUGH A VEERING LOW-LEVEL WIND FIELD WITH TIME SHOULD

TEND TO DIMINISH THE THREAT AFTER ABOUT 10-11Z.



AVIATION...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 30020.





...MEAD

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