WATCHES: Severe Thunderstorm Watch Number 690

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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