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933 

WWUS20 KWNS 142326

SEL0

SPC WW 142326

NEZ000-SDZ000-150700-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 660

NWS STORM PREDICTION CENTER NORMAN OK

525 PM MDT TUE SEP 14 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       WESTERN AND NORTHERN NEBRASKA

       SOUTHWEST AND SOUTH CENTRAL SOUTH DAKOTA



EFFECTIVE THIS TUESDAY AFTERNOON AND WEDNESDAY MORNING FROM 525

PM UNTIL 100 AM MDT.



TORNADOES...HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 80 STATUTE

MILES NORTH AND SOUTH OF A LINE FROM 90 MILES WEST NORTHWEST OF

MULLEN NEBRASKA TO 50 MILES NORTH NORTHEAST OF ONEILL NEBRASKA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU0).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



DISCUSSION...SCTD AREAS OF TSTMS EXPECTED TO MOVE/DEVELOP ENE ACROSS

WW AREA THOUGH EARLY WED AS WAA AND UPR LVL DIVERGENCE INCREASE

DOWNSTREAM FROM ERN WY/NRN CO UPR IMPULSE.  DEEP SHEAR AND

INSTABILITY SHOULD REMAIN FAVORABLE FOR SUPERCELLS THROUGH LATE

TONIGHT...WITH WITH MODERATE STRENGTHENING OF SLY LLJ CONTRIBUTING

TO ENHANCED LOW LVL SHEAR.  INCREASING CIN AFTER SUNSET MAY RESULT

IN MOST STORMS BEING SLIGHTLY ELEVATED.  BUT COMBINATION OF FAIRLY

RICH MOISTURE WITH INCREASING ASCENT AND LOW LVL SHEAR ALONG STALLED

FRONT ON THE NEB/SD BORDER SUGGESTS A NON-ZERO RISK FOR

TORNADOES...IN ADDITION TO SVR WIND/HAIL.



AVIATION...TORNADOES AND 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 26025.





...CORFIDI

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