

000 

WWUS20 KWNS 211904

SEL4

SPC WW 211904

COZ000-NEZ000-220400-



URGENT - IMMEDIATE BROADCAST REQUESTED

TORNADO WATCH NUMBER 154

NWS STORM PREDICTION CENTER NORMAN OK

200 PM CDT SAT APR 21 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

TORNADO WATCH FOR PORTIONS OF



       NORTHEAST COLORADO

       WESTERN AND CENTRAL NEBRASKA



EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 200 PM UNTIL

1100 PM CDT.



TORNADOES...HAIL TO 3 INCHES IN DIAMETER...THUNDERSTORM WIND

GUSTS TO 70 MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE

AREAS.



THE TORNADO WATCH AREA IS APPROXIMATELY ALONG AND 85 STATUTE

MILES EAST AND WEST OF A LINE FROM 20 MILES EAST SOUTHEAST OF

IMPERIAL NEBRASKA TO 25 MILES EAST NORTHEAST OF VALENTINE

NEBRASKA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU4).



REMEMBER...A TORNADO WATCH MEANS CONDITIONS ARE FAVORABLE FOR

TORNADOES AND 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.



DISCUSSION...TSTMS EXPECTED TO DEVELOP IN WRN AND SRN PARTS OF WW

OVER THE NEXT 2 HOURS OR SO AS LOW LEVEL CONVERGENCE AND HEATING

CONTINUE ALONG FRONT/LEE TROUGH EXTENDING NE FROM SE CO LEE LOW.

COUPLED WITH ARRIVAL OF INCREASED FORCING FOR ASCENT IN EXIT REGION

OF 80 KT NM MID LVL SPEED MAX...REGION WILL BE FAVORABLE FOR

LONG-LIVED SUPERCELLS.  DEGREE OF INSTABILITY...LOW LEVEL VEERING

PROFILES INVOF SW/NE FRONT...AND POTENTIAL FOR SOME STORMS TO MOVE

ALONG THE BOUNDARY SUGGEST A MODERATE PROBABILITY FOR TORNADOES IN

ADDITION TO LARGE HAIL AND POSSIBLY HIGH WIND.



AVIATION...TORNADOES AND 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

500. MEAN STORM MOTION VECTOR 22035.





...CORFIDI

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