

000 

WWUS20 KWNS 121859

SEL8

SPC WW 121859

NEZ000-130200-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 588

NWS STORM PREDICTION CENTER NORMAN OK

200 PM CDT SUN AUG 12 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       EASTERN NEBRASKA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 200 PM UNTIL 900

PM 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 NORTHWEST

OF GRAND ISLAND NEBRASKA TO 20 MILES SOUTH OF OMAHA NEBRASKA.

FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU8).



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...ELEVATED THUNDERSTORMS WILL INTENSIFY OVER NE NEB AND

LIKELY EVOLVE INTO A SMALL MCS ON THE COOL SIDE OF THE SURFACE FRONT

ACROSS SE NEB.  MODEST VERTICAL SHEAR AND INCREASING INSTABILITY

TOWARD SE NEB SHOULD SUPPORT AN INCREASING THREAT FOR LARGE HAIL AND

DAMAGING WINDS WITH THIS DEVELOPING STORM CLUSTER.

OTHERWISE...THERE IS SOME THREAT FOR MORE DISCRETE STORM DEVELOPMENT

ALONG THE SURFACE FRONT IN SE NEB LATER DURING THE AFTERNOON.

EFFECTIVE BULK SHEAR AND INSTABILITY APPEAR SUFFICIENT FOR

SUPERCELLS...AND AN ISOLATED TORNADO CANNOT BE RULED OUT GIVEN THE

MODEST LOW-LEVEL SHEAR AND BOUNDARY LAYER DEWPOINTS IN THE 70S.

HOWEVER...LARGE HAIL AND DAMAGING GUSTS SHOULD STILL BE THE PRIMARY

SEVERE THREATS WITH THIS ACTIVITY.



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 600. MEAN STORM

MOTION VECTOR 29025.





...THOMPSON

