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632 

WWUS20 KWNS 262246

SEL0

SPC WW 262246

NEZ000-SDZ000-270600-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 690

NWS STORM PREDICTION CENTER NORMAN OK

545 PM CDT TUE JUL 26 2011



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN AND CENTRAL NEBRASKA

       SOUTH-CENTRAL AND EASTERN SOUTH DAKOTA



EFFECTIVE THIS TUESDAY AFTERNOON AND WEDNESDAY MORNING FROM 545

PM UNTIL 100 AM 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 35 MILES EAST

SOUTHEAST OF IMPERIAL NEBRASKA TO 70 MILES NORTH NORTHEAST OF

VALENTINE NEBRASKA.  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 686...WW 687...WW

688...WW 689...



DISCUSSION...TSTMS SHOULD CONTINUE TO INCREASE IN COVERAGE AND

INTENSITY THIS EVENING ALONG PRE-FRONTAL TROUGH WHERE AIR MASS HAS

BECOME QUITE HOT WITH MLCAPE VALUES ESTIMATED TO BE AROUND 1500-3000

J/KG.  WHILE DEEP-LAYER WIND FIELD AND ASSOCIATED VERTICAL SHEAR

DECREASES WITH SWD EXTENT ACROSS WATCH AREA...THE MODERATE/STRONG

INSTABILITY AND STEEP LOW-LEVEL LAPSE RATES WILL FOSTER DAMAGING

DOWNDRAFT POTENTIAL.  UPSCALE GROWTH INTO AN MCS APPEARS LIKELY

TONIGHT AS INFLOW IS ENHANCED BY A DEVELOPING LLJ WITH A CONTINUED

THREAT FOR DAMAGING WINDS.



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 550. MEAN STORM

MOTION VECTOR 26020.





...MEAD

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