FXUS66 KMTR 260003
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
400 PM PST FRI DEC 25 2009 ... CHRISTMAS DAY

UPDATED AVIATION DISCUSSION

.DISCUSSION...AS OF 1:45 PM PST FRIDAY...SKIES ARE SUNNY ACROSS THE
DISTRICT WITH TEMPS IN THE 50S AND 60S. IN FACT...VIS IMAGERY IS INDC
CLEAR SKIES ACROSS THE ENTIRE STATE.

A RIDGE IS CENTERED ALONG THE COAST THIS AFTN WITH A COLD FRONT ALONG
130W. A SHORTWAVE EJECTING FROM THE MAIN UPPER LOW IN THE GULF OF
ALASKA WILL HELP PINCH OFF THE RIDGE IN SW CANADA. AS THE SHORTWAVE
APPROACHES THE COAST IT WILL SPLIT...WITH A CUTOFF LOW FORMING NEAR
130W...DROPPING SSE AS THE WEAKER NORTHERN PORTION BUTTS UP AGAINST
THE RIDGE. MODELS CONTINUE TO HAVE PROBLEMS WITH THIS PATTERN FOR THE
WEEKEND...WITH THE GFS THE DRIEST AND THE CANADIAN THE WETTEST. THE
NAM12 AND THE ECMWF ARE IN THE MIDDLE. THE COLD FRONT WILL WEAKEN AS
IT MOVES TOWARDS THE COAST...GIVING THE DISTRICT A CHANCE OF RAIN SAT
AFTN...WITH RAIN CHANCES CONTINUING ACROSS MOST OF THE DISTRICT SAT
NIGHT AND SUNDAY AS THE OVERALL TROUGH WILL BE SLOW TO MOVE.

NEXT WEEK WILL FEATURE A NW FLOW ALOFT OVER THE DISTRICT WITH A
MAINLY FLAT RIDGE OVER THE EASTERN PACIFIC AS THE PATTERN FAVORS A
TROUGH OVER THE CENTRAL AND EASTERN PORTIONS OF THE US. MEDIUM RANGE
MODELS CONTINUE TO BE IN DISAGREEMENT WITH THE DETAILS...BUT WEAK
SYSTEMS WILL RIDE OVER THE RIDGE INTO THE PACIFIC NW AND NORTHERN CA.
THE NORTH BAY WILL BE ON THE EDGE OF THE PRECIPITATION SHIELD...WITH
SLIGHT CHANCES OF SHOWERS THROUGH A GOOD PORTION OF THE WEEK. THE 12Z
GFS ENSEMBLES ARE IN GENERAL AGREEMENT WITH A NW FLOW OVER THE
DISTRICT FOR THE NEXT 7 TO 10 DAYS...NOT A VERY WET PATTERN FOR
CENTRAL CALIFORNIA.

&&

.AVIATION...AS OF 4:00 PM FRIDAY...CHRISTMAS DAY...HIGH PRESSURE
ALOFT AND AT THE SURFACE OVER THE GREAT BASIN WILL MAINTAIN LIGHT
OFFSHORE FLOW TENDENCIES FOR THE FORECAST AREA THROUGH MUCH OF
SATURDAY. CAVU/VFR CONDITIONS TO PREVAIL WITH EXCEPTION OF LATE
NIGHT/EARLY MORNING FREEZING FOG VICINITY OF KSTS. NORTH BAY
VALLEYS AND S.F.BAY AREA TERMINALS CAN EXPECT DEVELOPING -SHRA
AROUND 00Z SATURDAY AFTERNOON WITH AN APPROACHING COLD-FRONT.
CEILINGS AND VISIBILITIES TO LOWER TO MVFR DURING SATURDAY EVENING
THOSE AREAS WITH THE FRONT.

VICINITY OF KSFO...VFR CONDITIONS THROUGH SATURDAY AFTERNOON UNTIL
AROUND 00Z. MID-LEVEL CEILING BKN100-130 BY 21Z AND LOWERING BKN-
OVC050 BY 00Z. GENERALLY WINDS WILL BE LIGHT NORTHWEST LESS THAN
8 KTS THROUGH THE EVENING BUT BECOME DEFINITIVE FROM THE SOUTHEAST
5-10KT BY DAWN/14Z SATURDAY MORNING.

KSFO BRIDGE APPROACH...SAME AS KSFO.

MRY BAY AREA TERMINALS...VFR CONDITIONS THROUGH SATURDAY AFTERNOON
THROUGH 00Z. WINDS LIGHT AND GENERALLY SOUTHEAST 3-8KTS OVERNIGHT.
INCREASING SOUTHEAST WINDS 7-12KTS AFTER 14Z SATURDAY MORNING
AND THROUGH DAY WITH THE APPROACHING COLD-FRONT.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
   .TNGT...NONE.

$$

PUBLIC FORECAST: MHS
AVIATION/MARINE: GDUGEL

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO