WATCHES: Severe Thunderstorm Watch Number 859

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

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