

000 

WWUS20 KWNS 240347

SEL3

SPC WW 240347

IAZ000-NEZ000-SDZ000-241100-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 743

NWS STORM PREDICTION CENTER NORMAN OK

1045 PM CDT WED JUL 23 2008



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN IOWA

       NORTHEAST AND PARTS OF EASTERN NEBRASKA

       EXTREME SOUTHEAST SOUTH DAKOTA



EFFECTIVE THIS WEDNESDAY NIGHT AND THURSDAY MORNING FROM 1045 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 65

STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES NORTH OF

YANKTON SOUTH DAKOTA TO 35 MILES SOUTH SOUTHEAST OF OMAHA

NEBRASKA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).



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 741...WW 742...



DISCUSSION...STORMS ARE FORECAST TO INCREASE ALONG EASTERN GRADIENT

OF CENTRAL PLAINS INSTABILITY AXIS AS WEAK HEIGHT FALLS AND

INCREASINGLY STRONG LOW LEVEL JET AID ASCENT ACROSS THE REGION.

INFLOW AIR MASS IS STRONGLY UNSTABLE AND EFFECTIVE SHEAR OF 40-50KT

WILL SUPPORT UPDRAFT ROTATION AND PERSISTENCE WITH THE STRONGER

CELLS...GENERALLY ROOTED ABOVE 850MB. PRIMARY THREAT WITH THIS

OVERNIGHT ACTIVITY SHOULD BE LARGE HAIL. GRADUAL UPSCALE EVOLUTION

INTO A SMALL/COMPACT MCS WITH STRONG/DAMAGING WINDS IS POSSIBLE AS

COLD POOL STRENGTHENS AND MESOSCALE FORCING/LIFT IS ENHANCED WITHIN

STRONGLY UNSTABLE REGIME.



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 29025.





...CARBIN

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