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URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 271

NWS STORM PREDICTION CENTER NORMAN OK

1140 AM CDT THU MAY 10 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       SOUTH-CENTRAL AND DEEP SOUTH TEXAS

       COASTAL WATERS



EFFECTIVE THIS THURSDAY MORNING AND EVENING FROM 1140 AM UNTIL

800 PM CDT.



TORNADOES...HAIL TO 3 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 75 STATUTE

MILES EAST AND WEST OF A LINE FROM 55 MILES NORTHEAST OF COTULLA

TEXAS TO 25 MILES EAST SOUTHEAST OF MCALLEN TEXAS.  FOR A

COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE

UPDATE (WOUS64 KWNS WOU1).



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.



OTHER WATCH INFORMATION...CONTINUE...WW 270...



DISCUSSION...TSTMS /INCLUDING SUPERCELLS/ ARE ONGOING AS OF LATE

MORNING INVOF A STATIONARY BOUNDARY WHICH EXTENDS FROM N OF LRD TO

NEAR OR JUST S OF PSX.  AIR MASS ALONG AND S OF THIS BAROCLINIC ZONE

IS QUITE MOIST WITH DEWPOINTS IN THE UPPER 60S-LOWER 70S.  WHEN

COUPLED WITH DAYTIME HEATING AND STEEP MIDLEVEL LAPSE RATES...EXPECT

ENVIRONMENT TO BECOME MODERATE-STRONGLY UNSTABLE BY AFTERNOON WITH

MLCAPE APPROACHING 1500-3000 J/KG.  THIS INSTABILITY WILL ALIGN WITH

A STEADILY STRENGTHENING DEEP-LAYER WIND FIELD /AND VERTICAL SHEAR/

OWING TO THE EWD-DEVELOPMENT OF MID AND UPPER-LEVEL JET STREAKS

ACROSS THE LOWER RIO GRANDE VALLEY.  AS SUCH...SETUP IS EXPECTED TO

BECOME INCREASINGLY SUPPORTIVE OF INTENSE SUPERCELLS CAPABLE OF VERY

LARGE HAIL...TORNADOES...AND DAMAGING WINDS.



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

SURFACE AND ALOFT TO 3 INCHES. EXTREME TURBULENCE AND SURFACE

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

550. MEAN STORM MOTION VECTOR 27030.





...MEAD

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