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WWUS20 KWNS 030023

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 421

NWS STORM PREDICTION CENTER NORMAN OK

720 PM CDT THU JUN 2 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL NORTH DAKOTA

       WESTERN AND CENTRAL SOUTH DAKOTA



EFFECTIVE THIS THURSDAY NIGHT AND FRIDAY MORNING FROM 720 PM

UNTIL 300 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 60

STATUTE MILES EAST AND WEST OF A LINE FROM 80 MILES SOUTH

SOUTHWEST OF PHILIP SOUTH DAKOTA TO 50 MILES NORTHEAST OF

BISMARCK NORTH 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.



OTHER WATCH INFORMATION...CONTINUE...WW 419...WW 420...



DISCUSSION...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND

INTENSITY THIS EVENING ALONG COLD FRONT PUSHING EWD ACROSS THE WATCH

AREA.  00Z RAP/BIS SOUNDINGS SHOWED THE PRESENCE OF A VERY STEEP

LAPSE RATE ENVIRONMENT...WHICH WHEN COUPLED WITH MODEST BOUNDARY

LAYER MOISTURE...WAS RESULTING IN MLCAPE VALUES OF 2000-3000 J/KG.

MOREOVER...THESE OBSERVATIONS SAMPLED THE PRESENCE OF 30-50 KT SWLY

WINDS ABOVE 3 KM AGL WHICH WILL FAVOR ORGANIZED STORM MODES

INCLUDING SUPERCELLS AND BOWING STRUCTURES.  THOUGH A BRIEF TORNADO

IS POSSIBLE...DAMAGING WINDS AND LARGE HAIL APPEAR TO BE THE PRIMARY

HAZARDS.



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 24030.





...MEAD

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