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WWUS20 KWNS 211937

SEL5

SPC WW 211937

ARZ000-KSZ000-MOZ000-OKZ000-220300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 175

NWS STORM PREDICTION CENTER NORMAN OK

235 PM CDT THU APR 21 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN ARKANSAS

       SOUTHEAST KANSAS

       SOUTHWEST MISSOURI

       EASTERN OKLAHOMA



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 235 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 80

STATUTE MILES EAST AND WEST OF A LINE FROM 50 MILES SOUTH

SOUTHEAST OF POTEAU OKLAHOMA TO 65 MILES NORTH NORTHEAST OF

JOPLIN MISSOURI.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU5).



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...ELEVATED TSTMS ARE INCREASING IN COVERAGE AND INTENSITY

THIS AFTERNOON ALONG A SSWLY LLJ WHICH HAS STRENGTHENING TO 30-40

KT.  THIS LLJ WILL CONTINUE TO DEVELOP NEWD TOWARD THE MID MS VALLEY

BY EVENING IN ADVANCE OF A MIDLEVEL VORTICITY MAXIMUM TRANSLATING

ENEWD ACROSS THE CNTRL AND SRN PLAINS.  THE INCREASING MOISTURE ATOP

A STABLE BOUNDARY LAYER AND BELOW MIDLEVEL LAPSE RATES OF 7-8 C/KM

IS YIELDING A MODERATELY UNSTABLE ENVIRONMENT WITH MUCAPE VALUES OF

1500-2500 J/KG.  WHEN COUPLED WITH EFFECTIVE BULK SHEAR OF 35-45

KT...SETUP WILL SUPPORT THE DEVELOPMENT OF SUPERCELLS CAPABLE OF

LARGE HAIL.



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 25035.





...MEAD

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