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000 

WWUS20 KWNS 271934

SEL2

SPC WW 271934

IAZ000-NEZ000-SDZ000-280300-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 762

NWS STORM PREDICTION CENTER NORMAN OK

230 PM CDT SUN JUL 27 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       CENTRAL AND SOUTHERN IOWA

       EXTREME NORTHEAST NEBRASKA

       EXTREME SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 230 PM UNTIL

1000 PM CDT.



HAIL TO 3 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 120

STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES EAST

NORTHEAST OF STORM LAKE IOWA TO 45 MILES SOUTH OF KNOXVILLE IOWA.

 FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU2).



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 759...WW 760...WW 761...



DISCUSSION...THUNDERSTORMS HAVE SHOWN SIGNS OF INTENSIFICATION ALONG

AN OUTFLOW BOUNDARY AND IN ADVANCE OF AN MCV ASSOCIATED WITH THE

REMNANTS OF OVERNIGHT/MORNING STORMS IN MN/IA.  THE BOUNDARY LAYER

CONTINUES TO WARM AND MOISTEN TO THE S OF THE OUTFLOW BOUNDARY AND

SW OF A WARM FRONT IN ERN IA...AND CONVECTIVE INHIBITION WILL

CONTINUE TO WEAKEN THROUGH THE AFTERNOON.  STRONG WARM SECTOR

INSTABILITY /MLCAPE VALUES OF 2500-4000 J/KG/ AND ENHANCED VERTICAL

SHEAR WITH THE MCV WILL SUPPORT A THREAT FOR SUPERCELLS WITH VERY

LARGE HAIL AND DAMAGING WINDS.  THERE WILL BE SOME THREAT FOR AN

ISOLATED TORNADO WITH EARLY/DISCRETE STORMS ALONG THE

OUTFLOW...THOUGH THE PRIMARY THREAT WILL TRANSITION TO DAMAGING

WINDS/HAIL AS A RESULT OF STORM MERGERS/INTERACTIONS LATER THIS

AFTERNOON INTO EARLY TONIGHT.



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

TO 3 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 600. MEAN STORM

MOTION VECTOR 32025.





...THOMPSON

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