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000 

WWUS20 KWNS 120341

SEL7

SPC WW 120341

IAZ000-MOZ000-NEZ000-121000-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 687

NWS STORM PREDICTION CENTER NORMAN OK

1045 PM CDT FRI JUL 11 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       MUCH OF IOWA

       SMALL PART OF NORTHWEST MISSOURI

       PARTS OF SOUTHEAST NEBRASKA



EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 1045 PM

UNTIL 500 AM CDT.



HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 80

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.



THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 55 MILES SOUTHWEST

OF OMAHA NEBRASKA TO 65 MILES EAST NORTHEAST OF WATERLOO IOWA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU7).



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 684...WW 685...WW 686...



DISCUSSION...CAP HAS WEAKENED ALLOWING FRONTAL CONVERGENCE TO

SUPPORT DEVELOPMENT OF SEVERE THUNDERSTORMS IN THE VERY UNSTABLE

WARM SECTOR.  WITH THE 30-40 KT LLJ COUPLED WITH DEEP LAYER SHEAR

AND MLCAPES AOA 3000 J/KG...WIND DAMAGE WILL BE THE PRIMARY THREAT

AS STORMS EVOLVE INTO MULTICELL CLUSTERS AND BOWING LINE SEGMENTS.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 70

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM

MOTION VECTOR 26030.





...HALES

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