

000 

WWUS20 KWNS 112000

SEL1

SPC WW 112000

NEZ000-SDZ000-120300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 821

NWS STORM PREDICTION CENTER NORMAN OK

300 PM CDT MON AUG 11 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL NEBRASKA

       CENTRAL SOUTH DAKOTA



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 300 PM UNTIL

1000 PM 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 70

STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES SOUTHWEST OF

NORTH PLATTE NEBRASKA TO 50 MILES WEST NORTHWEST OF ABERDEEN

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.



DISCUSSION...THUNDERSTORM INCREASING LATE THIS AFTERNOON AHEAD OF

APPROACHING SHORTWAVE TROUGH AND ASSOCIATED MID LEVEL SPEED MAX.

PRIMARY DEVELOPMENT SHOULD OCCUR ALONG AND EAST OF SURFACE FRONT

EXTENDING ACROSS CENTRAL NEB/SD...WHERE AXIS OF MODERATE INSTABILITY

IS IN PLACE.  SHEAR WILL BE MODERATE...BUT STILL SUFFICIENT FOR

ORGANIZED LINES/CLUSTERS AND BRIEF-LIVED SUPERCELLS.  LARGE HAIL

WILL BE PRIMARY SEVERE THREAT...ESPECIALLY WITH INITIAL DEVELOPMENT

GIVEN THE RELATIVELY COLD AIR ALOFT...ALTHOUGH ISOLATED WIND DAMAGE

IS ALSO EXPECTED.  SHOULD ONE OR MORE LINEAR CLUSTERS EVOLVE THIS

EVENING...WIND DAMAGE POTENTIAL WILL LIKEWISE INCREASE.



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 500. MEAN STORM

MOTION VECTOR 28020.





...EVANS

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