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603 

WWUS20 KWNS 180414

SEL1

SPC WW 180414

IAZ000-NEZ000-181100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 671

NWS STORM PREDICTION CENTER NORMAN OK

1115 PM CDT FRI SEP 17 2010



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WEST CENTRAL IOWA

       CENTRAL AND EAST CENTRAL NEBRASKA



EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 1115 PM

UNTIL 600 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 45

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 30 MILES WEST

NORTHWEST OF BROKEN BOW NEBRASKA TO 10 MILES EAST NORTHEAST OF

DES MOINES IOWA.  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...LOW-MIDLEVEL FRONTOGENESIS AND WAA N OF A SURFACE COLD

FRONT WILL SUPPORT AN INCREASE IN ELEVATED CONVECTION IN AN E-W BAND

FROM CENTRAL NEB INTO WRN IA.  A RESERVOIR OF MODERATE MUCAPE AND

STEEP MIDLEVEL LAPSE RATES WILL SUPPORT STRONG UPDRAFTS...AND A FEW

ORGANIZED/SUPERCELL STORMS WILL BE POSSIBLE GIVEN 40+ KT EFFECTIVE

BULK SHEAR.  LARGE HAIL SHOULD BE THE PRIMARY SEVERE STORM THREAT

THROUGH THE OVERNIGHT HOURS.



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 28025.





...THOMPSON

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