

587 

WWUS20 KWNS 022133

SEL8

SPC WW 022133

CAZ000-ORZ000-030400-



URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 648

NWS STORM PREDICTION CENTER NORMAN OK

235 PM PDT SUN AUG 2 2009



THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF



       PARTS OF NORTHERN CALIFORNIA

       PARTS OF SOUTHERN OREGON



EFFECTIVE THIS SUNDAY AFTERNOON AND EVENING FROM 235 PM UNTIL 900

PM PDT.



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 75

STATUTE MILES EAST AND WEST OF A LINE FROM 25 MILES EAST

SOUTHEAST OF MOUNT SHASTA CALIFORNIA TO 40 MILES NORTH NORTHEAST

OF REDMOND OREGON.  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...COMBINATION OF VERY STEEP LAPSE RATES...MLCAPES E OF

CASCADES AOA 1500 J/KG AND 30KT OF DEEP LAYER SHEAR SUPPORT

DEVELOPMENT OF STRONG/SEVERE THUNDERSTORMS ACROSS HIGHER TERRAIN OF

SRN OR INTO BORDER AREAS OF NRN CA.  STORMS WILL DEVELOP/MOVE INTO

LOWER ELEVATIONS AND PRIMARY THREAT WILL BE LARGE HAIL AND LOCAL

DAMAGING DOWNBURST WINDS.



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 15020.





...HALES

