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640 

WWUS20 KWNS 012059

SEL7

SPC WW 012059

NEZ000-SDZ000-WYZ000-020400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 457

NWS STORM PREDICTION CENTER NORMAN OK

300 PM MDT THU AUG 1 2013



THE NWS STORM PREDICTION CENTER HAS ISSUED A



* SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

  WESTERN NEBRASKA INCLUDING THE PANHANDLE

  SOUTHWEST SOUTH DAKOTA

  EASTERN WYOMING



* EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 300 PM UNTIL

  1000 PM MDT.



* PRIMARY THREATS INCLUDE...

  SEVERAL LARGE HAIL EVENTS WITH A FEW VERY LARGE HAIL EVENTS TO 2

    INCHES IN DIAMETER POSSIBLE

  SEVERAL DAMAGING WIND GUSTS TO 70 MPH POSSIBLE



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 90

STATUTE MILES EAST AND WEST OF A LINE FROM 20 MILES EAST

SOUTHEAST OF SIDNEY NEBRASKA TO 90 MILES NORTH NORTHEAST OF

DOUGLAS WYOMING.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU7).



PRECAUTIONARY/PREPAREDNESS ACTIONS...



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...CONTINUE...WW 454...WW 455...WW 456...



DISCUSSION...TSTMS ARE INTENSIFYING OFF THE HIGH TERRAIN OF SERN WY

WITH ADDITIONAL STORM DEVELOPMENT ANTICIPATED THIS AFTERNOON INTO

EVENING ALONG A COMPOSITE BOUNDARY PRESENT ACROSS NWRN NEB/SWRN SD.

THE AMBIENT ENVIRONMENT IS MODERATELY UNSTABLE WITH MLCAPE OF

1500-2500 J/KG.  WHEN COUPLED WITH 35-45 KT OF DEEP-LAYER

SHEAR...THE SETUP APPEARS FAVORABLE FOR SUPERCELLS CAPABLE OF LARGE

HAIL AND DAMAGING WIND GUSTS.



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 30020.





...MEAD

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