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000 

WWUS20 KWNS 181958

SEL1

SPC WW 181958

SDZ000-WYZ000-190300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 531

NWS STORM PREDICTION CENTER NORMAN OK

155 PM MDT WED JUL 18 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN AND CENTRAL SOUTH DAKOTA

       EXTREME NORTHEAST WYOMING



EFFECTIVE THIS WEDNESDAY AFTERNOON AND EVENING FROM 155 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 70

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 25 MILES SOUTH OF

MOORCROFT WYOMING TO 50 MILES SOUTHEAST OF PIERRE 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.



OTHER WATCH INFORMATION...CONTINUE...WW 529...WW 530...



DISCUSSION...THUNDERSTORMS HAVE DEVELOPED RAPIDLY OVER PARTS OF WRN

SD WITHIN REGION OF VERY MOIST UPSLOPE FLOW WHERE MLCAPE IS

2000-3000 J/KG.  WATER VAPOR IMAGERY SHOWS SHORT WAVE TROUGH MOVING

EWD TOWARD THE REGION WHICH WILL PROVIDE INCREASED DYNAMIC SUPPORT

FOR LARGE SCALE ASCENT.  WESTERLY MID LEVEL WINDS OF 30 KT ATOP

ENELY LOW LEVEL WINDS ARE RESULTING IN DEEP LAYER SHEAR OF 40 KT

WHICH WILL ENHANCE STORM ORGANIZATION...INCLUDING POTENTIAL FOR MID

LEVEL ROTATION.  ACTIVITY MAY EVENTUALLY GROW UPSCALE LATER THIS

AFTERNOON OR EVENING  AS STORMS BEGIN TO MOVE EWD/ESEWD 15-20 KT.

LARGE HAIL AND DAMAGING WINDS WILL BE THE PRIMARY THREATS ALTHOUGH

AN ISOLATED TORNADO MAY ALSO BE POSSIBLE.



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 26020.





...WEISS

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