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ARZ000-LAZ000-MSZ000-TXZ000-271500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 226

NWS STORM PREDICTION CENTER NORMAN OK

455 AM CDT WED APR 27 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       SOUTHERN ARKANSAS

       NORTHERN LOUISIANA

       A SMALL PART OF WESTERN MISSISSIPPI

       NORTHEAST TEXAS



EFFECTIVE THIS WEDNESDAY MORNING FROM 455 AM UNTIL 1000 AM 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 100

STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES NORTH

NORTHWEST OF MONTICELLO ARKANSAS TO 40 MILES SOUTH OF SHREVEPORT

LOUISIANA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU6).



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.



OTHER WATCH INFORMATION...THIS SEVERE THUNDERSTORM WATCH REPLACES

TORNADO WATCH NUMBER 222. WATCH NUMBER 222 WILL NOT BE IN EFFECT

AFTER 455 AM CDT. CONTINUE...WW 223...WW 224...WW 225...



DISCUSSION...ELEVATED CONVECTION IS INCREASING IN COVERAGE/INTENSITY

IN RESPONSE TO LOW-LEVEL WAA ATOP A COLD POOL FROM EARLIER STORMS

ACROSS LA/MS/AR.  A FEED OF RICH MOISTURE FROM S OF THE BOUNDARY

WILL MAINTAIN MODERATE INSTABILITY...WHILE DEEP-LAYER VERTICAL SHEAR

IS FAVORABLE FOR ORGANIZED STORMS...INCLUDING SUPERCELLS.  LARGE

HAIL WILL BE THE MAIN SEVERE THREAT...THOUGH DAMAGING WINDS COULD

PENETRATE THE SHALLOW COLD POOL WITH ANY CELL MERGERS AND UPSCALE

GROWTH INTO CLUSTERS.  THE SRN PART OF THE WATCH AREA WILL CONTINUE

TO BE MONITOR FOR MORE SURFACE-BASED STORMS ALONG THE BOUNDARY.



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 550. MEAN STORM

MOTION VECTOR 26040.





...THOMPSON

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