FXUS66 KSTO 261151
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
330 AM PST SAT DEC 26 2009

.DISCUSSION...
HIGH CLOUDINESS AHEAD OF FRONTAL BAND NOW AT ABOUT 127 WEST OFF THE 
NORCAL COAST IS SPILLING OVER THE FORECAST AREA AT THIS TIME. SOME 
LIGHT FOG HAS FORMED AGAIN IN THE SOUTHERN SAC AND NORTHERN SAN 
JOAQUIN VALLEYS BUT THICKENING CLOUD DECK HAS KEPT THIS FOG FROM 
BECOMING SIGNIFICANT AND IN THE CASE OF SAC EXEC AIRPORT VISIBILITY 
HAS IMPROVED DURING THE NIGHT. WEAK OFFSHORE FRONT FORECAST TO MOVE 
ONSHORE AROUND 00Z THIS AFTERNOON THEN INLAND DURING THE NIGHT. THIS 
SYSTEM WILL WEAKEN MORE AS IT ENCOUNTERS THE NARROW RIDGE NOW OVER 
THE WEST COAST SO PRECIP AMOUNTS ARE STILL NOT EXPECTED TO BE 
PARTICULARLY HEAVY AND GENERALLY UNDER A FEW TENTHS OF AN INCH EVEN 
IN OROGRAPHICALLY FAVORED AREAS. SECONDARY SHORTWAVE TROUGH NOW 
BETWEEN 130 AND 140 WEST WILL FOLLOW QUICKLY ON THE HEALS OF THIS 
FIRST SYSTEM MOVING INLAND SUNDAY MORNING. ALTHOUGH STRONGER THAN 
THE INITIAL SYSTEM...THIS SECONDARY SYSTEM WILL ENCOUNTER THE SAME 
FATE AS THE FIRST AS IT RUNS UP AGAINST THE UPPER RIDGE OVER THE 
WESTERN U.S. THEREFORE PRECIP AMOUNTS ON SUNDAY WILL LIKELY BE IN 
THE FEW TENTHS OF AN INCH RANGE. WITH SNOW LEVELS EXPECTED AROUND 
4000 FEET...COULD SEE A FEW INCHES OF SNOWFALL OVER THE SIERRA 
PASSES FOR RETURN HOLIDAY TRAVEL.

SOUTHERN BRANCH OF A SPLIT PACIFIC STORM TRACK IS FORECAST TO DIG 
SOUTHWARD ON MONDAY FORMING A TROUGH ALONG THE WEST COAST. ALTHOUGH 
MOST OF THE MOISTURE AND INSTABILITY ASSOCIATED WITH THIS TROUGH IS 
EXPECTED TO REMAIN WELL SOUTH OF THE CWA...INSTABILITY GENERATED BY 
THE TROUGH COULD BE ENOUGH TO PRODUCE A FEW MOUNTAIN SHOWERS OVER 
NORCAL AND HAVE KEPT SLIGHT CHANCE POPS OVER THE MOUNTAINS MONDAY 
AND MONDAY NIGHT. ANOTHER WEAK PACIFIC STORM SYSTEM IS FORECAST TO 
TRACK THROUGH THE PACIFIC NORTHWEST AND NORCAL LATE TUESDAY AND 
WEDNESDAY BRINGING AND INCREASED THREAT OF LIGHT RAIN AND MOUNTAIN 
SNOW. 

RATHER FLAT RIDGE FORMS OVER THE WEST COAST BY THE END OF NEXT WEEK. 
THIS SHOULD KEEP THE SOUTHERN CWA DRY BUT ALLOW FOR A CONTINUED 
THREAT OF PRECIP OVER THE NORTHERN FORECAST AREA. SMITH 

&&

.AVIATION...
AREAS OF MVFR VSBYS DUE TO BR FROM THE CENTRAL SACRAMENTO 
VALLEY...DELTA...AND THE NORTHERN SAN JOAQUIN VALLEY TIL 
19Z-20Z...WITH LOCAL LIFR/IFR IN FG TIL 18Z. OTHERWISE VFR UNTIL AFT 
00Z. AS UPPER LEVEL TROF APPROACHES THE CA COAST...MASS OF MID TO 
HIGH LEVEL CLOUDS IS BECOMING STRETCHED AS IT MOVES INTO THE 
DOWNSTREAM RIDGE. THIS WILL SLOW AND WEAKEN THE INITIAL FRONTAL 
BAND. -RA EXPECTED TO SPREAD FROM W TO E INTO THE INTERIOR VLY 
AROUND 00Z-02Z WITH CIGS LOWERING TO 4-5 KFT...BECOMING MVFR TO 
LOCAL IFR CIGS/VSBYS IN -RA/-SN OVER SIERNEV THIS EVENING...SNOW 
LEVEL 3500-5000 FT. UPPER LEVEL LOW NEARING 130W WILL MOVE INLAND BY 
12Z SUN WITH CHANCE OF -SHRA/MTN -SHSN OVER INTERIOR NORCAL DURING 
THE DAY ON SUN. 

&&

.STO WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$