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WWUS20 KWNS 172041

SEL3

SPC WW 172041

COZ000-KSZ000-NEZ000-SDZ000-180300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 783

NWS STORM PREDICTION CENTER NORMAN OK

240 PM MDT WED AUG 17 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHEAST COLORADO

       NORTHWEST KANSAS

       WESTERN AND CENTRAL NEBRASKA

       SOUTH CENTRAL SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 240 PM UNTIL

900 PM MDT.



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 80

STATUTE MILES EAST AND WEST OF A LINE FROM 60 MILES NORTH

NORTHWEST OF VALENTINE NEBRASKA TO 15 MILES SOUTH OF BURLINGTON

COLORADO.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).



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...THUNDERSTORMS ARE ALREADY DEVELOPING IN NE CO...AND NEW

DEVELOPMENT WILL BE POSSIBLE IN THE NEXT COUPLE OF HOURS FARTHER N

ACROSS NEB/SD ALONG THE SURFACE LEE TROUGH.  WEAKENING CONVECTIVE

INHIBITION...MLCAPE OF 2000-3000 J/KG...AND EFFECTIVE BULK SHEAR OF

40-50 KT WILL SUPPORT SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL AND

DAMAGING WINDS.  AN ISOLATED TORNADO CANNOT BE RULED OUT INVOF NW

KS/SW NEB WHERE LOW-LEVEL MOISTURE WILL BE MAXIMIZED AND 0-1 KM SRH

WILL APPROACH 100 M2/S2.  LATER THIS EVENING...STORM MERGERS COULD

LEAD TO UPSCALE GROWTH INTO ONE OR TWO SMALL CLUSTERS...WITH AN

ATTENDANT RISK FOR DAMAGING WINDS.



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 29020.





...THOMPSON

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