

000 

WWUS20 KWNS 092102

SEL6

SPC WW 092102

NEZ000-SDZ000-100400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 576

NWS STORM PREDICTION CENTER NORMAN OK

400 PM CDT THU AUG 9 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       NORTHERN NEBRASKA

       SOUTHERN SOUTH DAKOTA



EFFECTIVE THIS THURSDAY AFTERNOON AND EVENING FROM 400 PM UNTIL

1100 PM CDT.



HAIL TO 2.5 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 60

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 90 MILES WEST OF

VALENTINE NEBRASKA TO 35 MILES NORTHEAST OF ONEILL NEBRASKA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU6).



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...CONTINUE...WW 575...



DISCUSSION...HIGH-BASED THUNDERSTORMS HAVE DEVELOPED OVER THE NRN

PART OF CENTRAL NEB.  SATELLITE IMAGERY SHOWS ADDITIONAL CONVECTION

BEGINNING TO DEVELOP ACROSS THE BORDER INTO SWRN SD...AND A

THICKENING CU FIELD OVER NORTH CENTRAL NEB.  RELATIVELY COOL MID

LEVEL TEMPERATURES /-8C AT 500 MB/ COUPLED WITH VERY WARM LOW LEVEL

TEMPERATURES AND INCREASING MOISTURE WITH EWD EXTENT IS RESULTING

UNSTABLE ENVIRONMENT WITH MLCAPE OF 1500-2500 J/KG.  40 KT OF DEEP

LAYER SHEAR WILL AID IN STORM INTENSIFICATION WITH POTENTIAL FOR A

FEW SUPERCELLS TO DEVELOP.  VERY LARGE HAIL AND DAMAGING WIND GUSTS

WILL BE THE PRIMARY THREATS..WHICH SHOULD CONTINUE THROUGH THE

EVENING HOURS AS NOCTURNAL LLJ INTENSIFIES AFTER DARK.



AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 2.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM

MOTION VECTOR 25020.





...WEISS

