FXUS66 KMTR 251254
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
232 AM PST FRI DEC 25 2009

.DISCUSSION...AS OF 2:32 AM PST FRIDAY...SATELLITE IMAGERY
CURRENTLY SHOWS CLEAR SKIES OVER THE DISTRICT WITH A BATCH OF HIGH
CLOUDS OVER THE CENTRAL VALLEY AND LOW CLOUDS APPROACHING THE WEST
COAST FROM THE NORTHWEST. AREAS OF FOG ARE FORMING IN THE NORTH BAY
VALLEYS AS WELL AS IN THE EAST BAY. AT THIS TIME...WIDESPREAD
FORMATION IS NOT EXPECTED...BUT WHAT FOG THERE IS WILL LIKELY
HANG AROUND INTO ABOUT MID MORNING. THE REST OF THE DAY IS EXPECTED
TO BE MOSTLY SUNNY WITH HIGH TEMPERATURES SIMILAR TO THOSE ON
THURSDAY.

ON SATURDAY AN UPPER TROUGH...ASSOCIATED WITH A GULF OF ALASKA LOW
PRESSURE CENTER...IS PROGGED TO APPROACH THE WEST COAST. THE
ASSOCIATED FRONTAL BAND IS FORECAST TO MOVE ACROSS OUR AREA LATE ON
SATURDAY...ALTHOUGH LATEST MODEL RUNS HAVE BACKED OFF CONSIDERABLY
ON RAINFALL ESTIMATES WITH THIS SYSTEM. THE LATEST RUN OF THE GFS...
FOR EXAMPLE...BRINGS A FEW HUNDREDTHS OF AN INCH AT MOST TO THE
AREA BY SATURDAY NIGHT AS THE SYSTEM MOVES THROUGH. THE ECMWF...
THOUGH...BRINGS IN MORE...OVER A HALF INCH IN SOME AREAS...BY 12Z
SUNDAY. BOTH MODELS STILL INDICATE A SPLITTING SYSTEM WITH THE MAIN
PORTION SHIFTING TO THE SOUTH OF OUR CWA AND THE PARENT UPPER LOW
MOVING ONSHORE TO THE NORTH. THE ECMWF STILL BRINGS MORE SHOWER
POTENTIAL TO OUR AREA WITH THE NORTHERN UPPER LOW AS IT MOVES
ACROSS ON MONDAY WHILE THE GFS CONTINUES TO BE RATHER DRY. THE
CURRENT FORECAST REFLECTS MORE LIKE THE ECWMF SOLUTION IN THAT
SHOWER CHANCES ARE MENTIONED THROUGH THE WEEKEND...TAPERING OFF BY
TUESDAY. ANOTHER IMPULSE MOVING ACROSS NORTHERN CALIFORNIA ON
WEDNESDAY IS EXPECTED TO BRING ADDITIONAL RAIN CHANCES TO THE AREA
BUT MAINLY THE NORTHERN HALF OF THE DISTRICT. BY THE END OF NEXT
WEEK A STRONGER FRONTAL SYSTEM IS FORECAST TO AFFECT THE DISTRICT.

&&

.AVIATION...AS OF 4:30 AM FRIDAY...HIGH PRESSURE OVER THE GREAT BASIN
WILL MAINTAIN LIGHT OFFSHORE FLOW THROUGH SATURDAY. VFR CONDITIONS
EXPECTED EXCEPT FOR MORNING FREEZING FOG AROUND STS.

VICINITY OF KSFO...VFR CONDITIONS THROUGH SATURDAY. LIGHT EAST
TO NORTHEAST WINDS WILL DEVELOP LATER THIS MORNING THEN SWITCH TO
NORTHWEST BY 00Z.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...VFR CONDITIONS THROUGH SATURDAY WITH LIGHT
EAST TO SOUTHEAST WINDS THROUGH THE MORNING. WINDS WILL SWITCH TO
LIGHT NORTHWESTERLY DURING THE AFTERNOON.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
   .TDA...NONE

$$

PUBLIC FORECAST: SSA
AVIATION/MARINE: W PI

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO