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000 

WWUS20 KWNS 142128

SEL3

SPC WW 142128

IAZ000-KSZ000-NEZ000-150400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 273

NWS STORM PREDICTION CENTER NORMAN OK

425 PM CDT MON MAY 14 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WEST CENTRAL IOWA

       NORTH CENTRAL KANSAS

       SOUTH CENTRAL INTO EAST CENTRAL NEBRASKA



EFFECTIVE THIS MONDAY AFTERNOON AND EVENING FROM 425 PM UNTIL

1100 PM CDT.



HAIL TO 1.5 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 50

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 70 MILES SOUTH

SOUTHWEST OF KEARNEY NEBRASKA TO 25 MILES NORTH NORTHEAST 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 271...WW 272...



DISCUSSION...THUNDERSTORMS ARE DEVELOPING ALONG THE SURFACE COLD

FRONT FROM SRN NEB INTO ERN NEB/WRN IA.  SURFACE TEMPERATURES OF

87-90 F HAVE HELPED ERODE THE CAP FROM BELOW...ALONG WITH ASCENT

FOCUSED ON THE BOUNDARY.  STEEP LAPSE RATES AND MLCAPE VALUES AROUND

2000 J/KG WILL SUPPORT A THREAT FOR LARGE HAIL WITH MULTICELL

CLUSTERS...WHILE VERTICAL SHEAR MAY BECOME MARGINALLY SUFFICIENT FOR

SUPERCELL STRUCTURES ALONG THE IMMEDIATE SURFACE BOUNDARY.

RELATIVELY LARGE TEMPERATURE-DEWPOINT SPREADS IN THE BOUNDARY LAYER

AND CELL MERGERS MAY SUPPORT DAMAGING DOWNBURST WINDS AS CONVECTION

SPREADS EWD/SEWD THROUGH THE EVENING.



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

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 27020.





...THOMPSON

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