

000 

WWUS20 KWNS 121906

SEL3

SPC WW 121906

COZ000-NEZ000-WYZ000-130200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 513

NWS STORM PREDICTION CENTER NORMAN OK

105 PM MDT THU JUL 12 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHEAST COLORADO

       CENTRAL AND SOUTHWEST NEBRASKA

       SOUTHEAST WYOMING



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 105 PM UNTIL

800 PM MDT.



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 15 MILES SOUTH

SOUTHWEST OF LARAMIE WYOMING TO 30 MILES EAST NORTHEAST OF GRAND

ISLAND 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.



DISCUSSION...THUNDERSTORMS WILL INCREASE IN COVERAGE/INTENSITY ALONG

A SURFACE TROUGH FROM SE WY INTO CENTRAL NEB THROUGH THE AFTERNOON.

MODERATE INSTABILITY IS PRESENT S OF THIS TROUGH...AND REGIONAL VAD

WINDS/PROFILERS...AS WELL AS THE 18Z LBF SOUNDING...SHOW WIND

PROFILES WITH SUFFICIENT VERTICAL SHEAR FOR SUPERCELLS.  THE

HODOGRAPH CURVATURE ACROSS THE SW NEB AREA ACTUALLY APPEARS TO FAVOR

LEFT-MOVING STORMS.  THE MORE FAVORABLE AREA FOR RIGHT-MOVING

SUPERCELLS WILL BE A SMALL AREA ACROSS SE WY ALONG A NW-SE ORIENTED

BOUNDARY...WHERE AN ISOLATED TORNADO MAY OCCUR.  ELSEWHERE ACROSS

THE WATCH AREA...LARGE HAIL AND DAMAGING WINDS WILL BE THE PRIMARY

THREATS...THOUGH A BRIEF TORNADO CANNOT BE RULED OUT GIVEN THE

EXPECTED SUPERCELL STRUCTURES AND RELATIVELY MOIST LOW-LEVEL

ENVIRONMENT.



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 31025.





...THOMPSON

