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282 

WWUS20 KWNS 222349

SEL0

SPC WW 222349

SDZ000-WYZ000-230700-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 420

NWS STORM PREDICTION CENTER NORMAN OK

550 PM MDT FRI JUN 22 2012



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN SOUTH DAKOTA

       NORTHEAST WYOMING



EFFECTIVE THIS FRIDAY AFTERNOON AND SATURDAY MORNING FROM 550 PM

UNTIL 100 AM 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 60

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

SOUTHWEST OF RAPID CITY SOUTH DAKOTA TO 75 MILES NORTH NORTHWEST

OF RAPID CITY SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE

WATCH SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU0).



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 417...WW 418...WW 419...



DISCUSSION...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE THIS EVENING

IN ADVANCE OF SHORTWAVE TROUGH APPROACHING THE REGION FROM THE WEST.

AMBIENT AIR MASS IS CHARACTERIZED BY STEEP LAPSE RATES...MLCAPE OF

1500-2500 J/KG AND WEAKENING INHIBITION.  WHEN COUPLED WITH

VERTICALLY VEERING WIND PROFILES AND STRENGTHENING DEEP-LAYER

SHEAR...ENVIRONMENT WILL SUPPORT SUPERCELLS CAPABLE OF LARGE HAIL

AND DAMAGING WINDS.  STORMS MAY GROW UPSCALE INTO AN MCS ACROSS

PARTS OF WRN SD TONIGHT IN EXIT REGION OF NOCTURNAL LLJ WITH A

CONTINUED RISK FOR HAIL AND HIGH 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 25025.





...MEAD

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