FXUS66 KMTR 060018
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
300 PM PST SAT DEC 5 2009

.DISCUSSION...AS OF 2:45 PM PST SATURDAY...THE LOW CLOUDS IN SAN
FRANCISCO'S EAST BAY AREA SOUTHWARD HAVE BEEN SLOWER TO CLEAR THAN
EXPECTED...BUT THEY ARE CLEARING. A MOSTLY CLEAR SKY TONIGHT WILL
ALLOW TEMPERATURES TO LOWER IN COLD VALLEY AND MOUNTAIN LOCATIONS
TO NEAR OR BELOW FREEZING AS A COLD AIR MASS CONTINUES TO MOVE
TOWARD THE SAN FRANCISCO AND MONTEREY BAY AREAS. THIS AIR MASS IS
ASSOCIATED WITH A SHORT WAVE TROUGH DIVING OUT OF CANADA...
UNDERCUTTING THE BLOCKING HIGH PRESSURE RIDGE IN THE GULF OF
ALASKA. THIS DISTURBANCE WILL BRING ENOUGH MOISTURE TO THE REGION TO
CAUSE RAIN AND MOUNTAIN SNOW SUNDAY NIGHT INTO MONDAY. THE COLDEST
AIR WILL ARRIVE AFTER THE CHANCES FOR PRECIPITATION BEGIN TO
DIMINISH SO SNOWFALL AMOUNTS ARE NOT EXPECTED TO BE SIGNIFICANT.
UNLESS...CONVECTIVE CELLS DEVELOP WHICH CAN PRODUCE BRIEF HEAVY
SNOW.

WITH THE VERY COLD AIR BEHIND THIS DISTURBANCE FREEZING TEMPERATURES
WILL RESULT PROMPTING THE ISSUANCE OF A FREEZE WATCH FOR MONDAY
NIGHT THROUGH TUESDAY MORNING. AREAS INLAND FROM THE COAST AND BAYS
CAN EXPECT TEMPERATURES TO LOWER INTO THE 20S AND LOWER 30S FOR
SEVERAL HOURS.

THE BLOCKING HIGH WILL REMAIN OVER THE GULF OF ALASKA THROUGH THE
WEEK PROVIDING A TRACK FOR MOIST WESTERLY FLOW TO BE DIRECTED INTO
CALIFORNIA. SHORT WAVE TROUGHS WILL SLIDE UNDER THE RIDGE CAUSING
PERIODS OF RAIN EVEN INTO THE WEEKEND. THE MODELS HAVE NOT COME INTO
FOCUS WITH RESPECT TO TIMING OF EACH IMPULSE...BUT AGREE THAT ON AND
OFF RAIN WILL BE PRESENT. AS WE GET CLOSER TO THE EVENTS DETAILS WILL
COME TOGETHER.

&&

.AVIATION...AS OF 4:00 PM PST SATURDAY...A COLD FRONT IS SLIDING
SOUTH INTO MONTEREY AND SAN BENITO COUNTIES. SKIES HAVE CLEARED OVER
THE SFO BAY AREA AND WILL CLEAR FROM THE SOUTHERN MRY BAY AREA
01-02Z. NORTHEAST WINDS DEVELOP ALOFT BEHIND THE FRONT. THIS
WILL KEEP THE SFO BAY AREA CLEAR THROUGH TONIGHT. THE MRY BAY AREA
IS NOT AFFECTED AS MUCH AND COULD STILL SEE PATCHY LOW CLOUDS
EARLY SUNDAY. WINDS ARE EXPECTED TO INCREASE THROUGH EARLY EVENING
AS COLDER UNSTABLE AIR ALLOWS WINDS ALOFT TO MIX TO THE GROUND.
WINDS SHOULD DECREASE AFTER MIDNIGHT.

VICINITY OF KSFO...VFR CONDITIONS THROUGH SUNDAY. WEST TO NORTHWEST
WINDS WILL INCREASE THROUGH EARLY EVENING TO 15 KT WITH POSSIBLE
GUSTS AS HIGH AS 20 KT. WINDS DECREASING TO 10 KT OR LESS AFTER 12Z.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...MVFR CIGS WILL PREVAIL THROUGH 01-02Z.
SKIES WILL CLEAR AFTER 04Z BUT PATCHY CLOUDS MAY REDEVELOP AFTER
12Z.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
    .TNGT...SCA PT ARENA TO PT PIEDRAS BLANCAS 10-60 NM
            SCA PT ARENA TO PT REYES 0-10 NM

$$

PUBLIC FORECAST: EVANS
AVIATION/MARINE: LARRY/W PI

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO