

435 

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

