

367 

WWUS20 KWNS 062033

SEL9

SPC WW 062033

NEZ000-SDZ000-WYZ000-070400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 859

NWS STORM PREDICTION CENTER NORMAN OK

235 PM MDT THU OCT 6 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN NEBRASKA

       SOUTHWEST SOUTH DAKOTA

       FAR EASTERN WYOMING



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 235 PM UNTIL

1000 PM MDT.



HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 75

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 105

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

NORTHWEST OF RAPID CITY SOUTH DAKOTA TO 45 MILES EAST OF SIDNEY

NEBRASKA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU9).



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...PV TAIL MIGRATING NNE AROUND GREAT BASIN UPR TROUGH

WILL CONTINUE INTO THE CNTRL/HIGH PLAINS THIS EVENING PROVIDING AN

INCREASE IN LARGE-SCALE FORCING FOR ASCENT.  ATTENDANT SFC LOW WILL

MIGRATE FROM NCNTRL CO ACROSS FAR ERN WY AND INTO SWRN SD.  LLVL

THETA-E AXIS WILL TEND TO MOVE WWD TO ALONG THE WY/NEB BORDER AND

INTO SWRN SD WITH TIME AND MLCAPES WILL RANGE FROM 500-1000 J/KG.

VERTICAL SHEAR WILL BE MORE THAN SUFFICIENT FOR INITIAL STORMS TO BE

SUPERCELLS WITH LARGE HAIL AND PERHAPS AN ISOLD TORNADO VCNTY THE

WRMFNT.  OTHERWISE...AS LARGE SCALE ASCENT SPREADS ENE...DEVELOPMENT

OF LINE SEGMENTS WITH EMBEDDED ROTATING STRUCTURES WILL BE POSSIBLE

THROUGH MID-EVENING ACROSS SWRN SD AND WRN NEB.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 65

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 21035.





...RACY

