DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 050055
SWODY1
SPC AC 050052

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0652 PM CST WED MAR 04 2009

VALID 050100Z - 051200Z

...NO SVR TSTM AREAS FORECAST...

...CALIFORNIA...
CLUSTER OF STORMS ROUGHLY 175 STATUTE MILES WEST OF SAN FRANCISCO
BAY AT 05/00Z APPEARS TO BE SUPPORTED BY FORCING ASSOCIATED WITH A
CYCLONIC VORTICITY CENTER EMBEDDED WITHIN A BROADER SCALE COLD UPPER
TROUGH ACROSS THE EASTERN PACIFIC/PACIFIC COAST STATES AND
INTERMOUNTAIN WEST. THIS FEATURE IS PROGGED TO APPROACH THE SAN
FRANCISCO BAY AREA TONIGHT...BUT WEAKEN BEFORE IT REACHES COASTAL
AREAS...AS ANOTHER STRONGER CIRCULATION FORMS IN ASSOCIATION WITH A
DIGGING JET STREAK OFFSHORE. AS THIS OCCURS...THE ONGOING SMALL
CLUSTER OF THUNDERSTORMS SEEMS LIKELY TO WEAKEN BEFORE SPREADING
INLAND.

MEANWHILE...ANOTHER MORE SUBSTANTIAL...BUT WEAKENING...CIRCULATION
CENTER HAS ALREADY MIGRATED INLAND ACROSS SOUTHERN OREGON AND
NORTHERN CALIFORNIA. THIS FEATURE SHOULD BECOME INCREASINGLY
SHEARED WITHIN A CONFLUENT UPPER FLOW REGIME...AS IT PROGRESSES EAST
NORTHEASTWARD ALONG/NORTH OF THE POLAR JET AXIS...INTO THE NORTHERN
INTERMOUNTAIN REGION OVERNIGHT.

IN BETWEEN THE TWO SYSTEMS...DESPITE THE WEAKNESS OF THE UPPER
SUPPORT FOR UPWARD VERTICAL MOTION...WIDELY SCATTERED STORMS ARE
ONGOING ACROSS THE NORTHERN SAN JOAQUIN AND SACRAMENTO VALLEYS OF
CALIFORNIA. DAYTIME HEATING BENEATH A VERY COLD MID-LEVEL AIR
MASS...CHARACTERIZED BY 500 MB TEMPERATURES AT OR BELOW -30C...SEEMS
TO BE THE PRIMARY FORCING FOR ACTIVITY...SOME OF WHICH MAY CONTINUE
TO BE ACCOMPANIED BY HAIL. CLOUD BEARING LAYER SHEAR IS RATHER
WEAK...BUT STEEP LAPSE RATES WITHIN A MIXED PHASE LAYER FAVORABLE
FOR THE DEVELOPMENT OF GRAUPEL AND HAIL GROWTH...ATOP COOL
THERMODYNAMIC PROFILES SUPPORTIVE OF LITTLE MELTING...ARE ALLOWING
FOR SOME SMALL TO PERHAPS MARGINALLY SEVERE HAIL...TO REACH THE
SURFACE. THIS GENERALLY SHOULD DIMINISH FAIRLY QUICKLY AROUND
SUNSET.

...NORTHERN HIGH PLAINS...
GIVEN THE LACK OF LOW-LEVEL MOISTURE TO THE LEE OF THE ROCKIES...
LOCALIZED THUNDERSTORM ACTIVITY DEVELOPING OFF THE BIG HORNS IS NOT
EXPECTED TO PERSIST MUCH LONGER...AS SUPPORTING MID-LEVEL FORCING
ASSOCIATED WITH A WEAK SHORT WAVE TROUGH LIFTS NORTHEAST OF THE
HIGHER TERRAIN THIS EVENING.

..KERR.. 03/05/2009

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