WATCHES: Severe Thunderstorm Watch Number 254

WWUS20 KWNS 060305
SEL4
SPC WW 060305
IAZ000-MNZ000-NEZ000-SDZ000-061000-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 254
NWS STORM PREDICTION CENTER NORMAN OK
1005 PM CDT SAT MAY 5 2012

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

NORTHWEST IOWA
SOUTHWEST MINNESOTA
CENTRAL AND NORTHEAST NEBRASKA
EXTREME SOUTHEAST SOUTH DAKOTA

EFFECTIVE THIS SATURDAY NIGHT AND SUNDAY MORNING FROM 1005 PM
UNTIL 500 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 55
STATUTE MILES NORTH AND SOUTH OF A LINE FROM 20 MILES SOUTH OF
NORTH PLATTE NEBRASKA TO 10 MILES NORTHEAST OF SPENCER IOWA. FOR
A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU4).

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...THIS SEVERE THUNDERSTORM WATCH REPLACES
TORNADO WATCH NUMBER 251. WATCH NUMBER 251 WILL NOT BE IN EFFECT
AFTER 1005 PM CDT. CONTINUE...WW 250...WW 252...WW 253...

DISCUSSION...CLUSTERS/BANDS OF ELEVATED STORMS CONTINUE TO EXPAND IN
COVERAGE ON THE COOL SIDE OF A SURFACE FRONT FROM CENTRAL NEB INTO
SE SD. A FEED OF STRONG INSTABILITY REMAINS S OF THE
BOUNDARY...WHERE LOW-LEVEL FLOW HAS INCREASED THE PAST FEW HOURS.
PRONOUNCED WAA AND THE INCREASING INFLUENCE OF THE MIDLEVEL TROUGH
EJECTING OVER THE NRN HIGH PLAINS WILL SUPPORT EVENTUAL EWD/SEWD
MOVEMENT OF THE FRONT AND ASSOCIATED CONVECTION OVERNIGHT. GIVEN
THE ELEVATED NATURE OF THE CONVECTION...LARGE HAIL WILL BE A PRIMARY
CONCERN...AS WELL AS DAMAGING WINDS THAT PENETRATE THROUGH THE
NEAR-SURFACE STABLE LAYER N OF THE FRONT.

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 25025.


...THOMPSON

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