WATCHES: Severe Thunderstorm Watch Number 648

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

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