FXUS66 KSTO 241157
AFDSTO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
330 AM PST THU DEC 24 2009

.DISCUSSION...
UPPER RIDGE ALONG THE WEST COAST BRINGING CLEAR SKIES THIS MORNING. 
SMF AIRPORT REPORTING FOG THIS MORNING BUT SO FAR THIS IS THE ONLY 
REPORTING STATION DOING SO SO WIDESPREAD FOG FORMATION IN THE VALLEY 
DOES NOT APPEAR WILL BE A MAJOR CONCERN. WITH TEMPERATURES IN THE 
CENTRAL VALLEY HOVERING AROUND FREEZING...MANY LOCATIONS LIKELY TO 
WAKE UP TO FROST OR FROSTY WINDSHIELDS. ONE PLACE THAT IS A LITTLE 
WARMER THIS MORNING IS THE REDDING AIRPORT WHERE A LITTLE STRONGER 
WINDS ARE BRINGING TEMPERATURES IN AROUND 10 DEGREES ABOVE 24 HOURS 
AGO. WITH ONLY SLIGHT SHIFT IN UPPER RIDGE TODAY...SHOULD SEE HIGH 
TEMPERATURES SIMILAR TO WEDNESDAYS. UPPER RIDGE AXIS CENTERS OVER 
THE WEST COAST ON FRIDAY FOR CONTINUED FAIR SKIES CHRISTMAS DAY. 
WITH SLIGHT INCREASE IN SUBSIDENCE...MAY SEE A BIT MORE FOG FRIDAY 
MORNING IN THE CENTRAL AND MOUNTAIN VALLEYS BUT MOISTURE PROGS NOT 
SHOWING SIGNIFICANT ACCUMULATION OF SURFACE MOISTURE SO WIDESPREAD 
FOG SHOULD NOT BE AN ISSUE. 

SOUTHERN PORTION OF FRONTAL BAND NOW AT 140 WEST FORECAST TO MOVE 
ONTO THE COAST BY SATURDAY AFTERNOON AS UPPER SHORTWAVE PIVOTS INTO 
THE PACIFIC NORTHWEST. PREVIOUS RUN OF THE GFS WAS A LITTLE FASTER 
WITH THIS SYSTEM BUT LATEST 06Z RUN OF THE GFS NOW CLOSER IN TIMING 
TO THE ECMWF. THEREFORE...MOST OF THE FORECAST AREA SHOULD SEE A DRY 
DAY SATURDAY WITH INCREASING CLOUDS WITH THE MAIN THREAT OF PRECIP 
REMAINING OVER THE COASTAL RANGE. LIGHT PRECIP MOVES OVER THE 
NORTHERN PORTION OF THE STATE SATURDAY NIGHT AS FRONT BREAKS APART. 
AT THIS POINT ANY PRECIP AMOUNTS...EVEN OVER OROGRAPHICALLY ENHANCED 
AREAS SHOULD REMAIN FAIRLY LIGHT. A SECOND PACIFIC SHORTWAVE IS 
FORECAST TO FORM A LOW AS IT DIGS SOUTHWARD OFF THE COAST ON SUNDAY. 
EARLIER MODEL RUNS SKIMMED THIS LOW CLOSE ENOUGH TO THE COAST TO 
BRING PRECIP THREAT TO ENTIRE CWA. LATEST 00Z RUNS HOWEVER KEEP THIS 
LOW FARTHER OFFSHORE AND BRING A DRIER SCENARIO FOR SUNDAY. WILL 
HAVE TO WAIT FOR SUBSEQUENT RUNS BUT IF THIS FARTHER OFFSHORE 
FORECAST HOLDS...SUNDAY AND MONDAY MAY BE A DRIER DAYS THAN 
PREDICTED IN CURRENT FORECAST PACKAGE. 

CONFIDENCE IN FORECAST CONTINUES TO ERODE FOR TUESDAY AND WEDNESDAY 
OF NEXT WEEK WITH SIGNIFICANT DIFFERENCES IN MODEL OUTPUT. ECMWF 
BRINGS ANOTHER PACIFIC FRONTAL SYSTEM INTO THE PACIFIC NORTHWEST AND 
NORCAL ON TUESDAY AND TUESDAY NIGHT WHILE GFS KEEPS MUCH STRONGER 
RIDGING IN PLACE AND RIDES A WEAKER SYSTEM WELL NORTH OF THE 
FORECAST AREA. CANADIAN MODEL SIDES WITH ECMWF AT THIS TIME SO HAVE 
LEFT SLIGHT CHANCE POPS IN FOR NOW FOR END OF THE FORECAST PERIOD. 

&&

.AVIATION...
SOME PATCHY FOG HAS DEVELOPED NEAR SMF AND NEAR MOD. DON'T EXPECT 
THE FOG TO EXPAND VERY MUCH MORE THAN WHAT IT IS RIGHT NOW THUS 
DOMINATE WEATHER WILL BE VFR CONDITIONS WITH THE PATCHY IFR DUE TO 
THE FOG THROUGH EARLY THIS MORNING. SURFACE WINDS WILL SLOWLY START 
TO BACK TOT HE SOUTH TOMORROW WHICH WILL INCREASE THE CHANCE OF FOG 
TOMORROW MORNING. RASCH

&&

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

&&

$$