

000 

WWUS20 KWNS 012251

SEL1

SPC WW 012251

NEZ000-SDZ000-020500-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 471

NWS STORM PREDICTION CENTER NORMAN OK

455 PM MDT SUN JUL 1 2007



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       WESTERN NEBRASKA PANHANDLE

       WESTERN SOUTH DAKOTA



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 455 PM UNTIL

1100 PM MDT.



HAIL TO 1.5 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 65

STATUTE MILES EAST AND WEST OF A LINE FROM 45 MILES SOUTH

SOUTHEAST OF SCOTTSBLUFF NEBRASKA TO 100 MILES NORTH OF PHILIP

SOUTH DAKOTA.  FOR A COMPLETE DEPICTION OF THE WATCH SEE THE

ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU1).



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 468...WW 469...WW 470...



DISCUSSION...DEEP MIXING FROM STRONG AFTERNOON HEATING AND

CONVERGENCE INVOF LEE TROUGH/SURFACE LOW WILL CONTINUE SUPPORTING

STRONG TO SEVERE THUNDERSTORMS THIS EVENING ACROSS WATCH AREA.

MLCAPE AROUND 1500 J/KG AND 25-35 KT DEEP LAYER SHEAR SHOULD SUSTAIN

A FEW STRONGER CORES WITH ATTENDANT THREATS OF LARGE HAIL AND

DAMAGING WINDS.  DOWNBURSTS SHOULD BE ENHANCED THIS EVENING GIVEN

THE VERY STEEP LOW LEVEL LAPSE RATES AND SFC T-TD SPREADS NEARING

50F.



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

TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60

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

MOTION VECTOR 31015.





...EVANS

