WATCHES: Tornado Watch Number 154

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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