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