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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 561

NWS STORM PREDICTION CENTER NORMAN OK

1110 AM MDT TUE AUG 3 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN SOUTH DAKOTA

       NORTHEAST WYOMING



EFFECTIVE THIS TUESDAY MORNING AND EVENING FROM 1110 AM UNTIL 600

PM MDT.



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 90

STATUTE MILES EAST AND WEST OF A LINE FROM 65 MILES NORTH OF

RAPID CITY SOUTH DAKOTA TO 70 MILES SOUTH OF RAPID CITY SOUTH

DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED

WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



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...A MIDLEVEL SHORTWAVE TROUGH AND BELT OF ASCENT WILL

CONTINUE TO SPREAD EWD TOWARD NE WY/WRN SD THROUGH THE AFTERNOON.

THUNDERSTORMS HAVE BEEN INCREASING THROUGH LATE MORNING IN ADVANCE

OF THIS WAVE...AND SURFACE-BASED STORM DEVELOPMENT APPEARS LIKELY BY

EARLY AFTERNOON.  GIVEN A COMBINATION OF EFFECTIVE BULK SHEAR NEAR

40 KT AND MODERATE INSTABILITY...A FEW SUPERCELLS AND ORGANIZED

MULTICELL CLUSTERS CAN BE EXPECTED.  DAMAGING WINDS AND LARGE HAIL

WILL BE THE MAIN THREATS AS STORMS BEGIN TO INTERACT/MERGE DURING

THE AFTERNOON...THOUGH AN ISOLATED TORNADO CANNOT BE RULED OUT WITH

THE MORE DISCRETE STORMS EARLY THIS AFTERNOON.



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 27020.





...THOMPSON

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