FXUS66 KMTR 021318
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA CA
515 AM PST WED DEC 2 2009

UPDATED FOR AVIATION DISCUSSION

.DISCUSSION...AS OF 4:30 AM PST WEDNESDAY...SHORT TERM FOCUS IS ON
DENSE FOG THIS MORNING. QUIET WX THIS AFTERNOON THROUGH SATURDAY.
THEN LONG RANGE FORECASTS WITH UPCOMING MAJOR WEATHER PATTERN
CHANGE.

IN THE SHORT TERM...AREAS OF DENSE FOG HAVE DEVELOPED OVERNIGHT
NEAR THE COAST/BAY AND VALLEYS. OAKLAND AIRPORT WAS RECENTLY 1/4
MILE WITH REDUCED VSBYS SHOWING UP AT SANTA ROSA AND WATSONVILLE
AIRPORTS OVERNIGHT. SPOTTER REPORTS OVERNIGHT INDICATE POCKETS OF
DENSE FOG THROUGHOUT THE REGION. THIS IS MORE OF A WINTERTIME SETUP
WITH VALLEY MOISTURE BEING TRAPPED AND SHALLOW GROUND FOG. EITHER
WAY EXPECT SOME TROUBLE FOR THE MORNING COMMUTE. GRIDS AND ZONES
HAVE TRIED TO CAPTURE THE CURRENT TRENDS. THE WORST LOCATIONS APPEAR
TO BE AROUND SF AND MONTEREY BAYS AT THIS HOUR.

AFTER THE FOG/LOW CLOUDS CLEAR EXPECT ANOTHER PARTLY CLOUDY AND
SEASONABLE DAY WITH HIGH TEMPS INTO THE LOWER 60S MOST LOCALES.

NO BIG WEATHER CHANGES ARE FORESEEN THE NEXT SEVERAL DAYS SO
PERSISTENCE MAY BE THE WAY TO GO AND HAVE PUT MORE COASTAL AND
VALLEY FOG INTO THE FORECAST AGAIN TONIGHT. NO STRONG GRADIENTS OR
WIND TO MIX THINGS OUT.

LOOKING AHEAD...THE MODELS ARE BRINGING AN ARCTIC PLUNGE OF AIR TO
THE PACIFIC NORTHWEST BY SATURDAY. THE HANDLING OF THE ASSOCIATED
TROUGH DIFFERS BETWEEN THE MODELS AND BEGINS THE PERIOD OF SOME
FORECAST UNCERTAINTY. IN GENERAL THE GFS DROPS THE COLD AIR FARTHER
SOUTH AND WEST TOWARDS NORTHERN CALIFORNIA AND THE NET RESULT IS
TO THEN SHIFT INCOMING JET STREAM ENERGY INTO SOUTHERN CALIFORNIA.
THE EURO KEEPS THE TROUGH AND ASSOCIATED COLD AIR FARTHER EAST
WHICH ALLOWS INCOMING WESTERLIES TO PLOW INTO THE WEST COAST. WERE
NOW GETTING INTO THE 5 DAY WINDOW AND THE GFS AND EURO ARENT REALLY
BUDGING WITH THEIR RESPECTIVE SOLUTIONS. HOWEVER YESTERDAYS 12Z
EURO WAS SIMILAR TO THE GFS BUT THE NEW 00Z EURO REVERTED BACK TO
ITS SOLUTION FROM 24 HOURS AGO. UPSHOT BEING THE EURO SOLUTION IS
MUCH WETTER BY SUNDAY NIGHT INTO MONDAY WITH THE FIRST STORM THAT
WOULD BRING STEADY RAINS INTO THE BAY AREA. THIS FORECASTER STILL
SIDES WITH THE EURO SOLUTIONS BUT FOR WHATS IT WORTH THE GFS RUNS
WOULD KEEP MONDAY MUCH COLDER (534 DM THICKNESS) WITH SHOWERY
WEATHER WHILE THE EURO BRINGS SIGNIFICANT WARM ADVECTION RAINS IN
FROM THE WEST. SO THE GREATEST FORECAST UNCERTAINTY STILL REMAINS
WITH WHEN THE WET/UNSETTLED WEATHER WILL DEVELOP.

THERE IS ACTUALLY BETTER MODEL AGREEMENT THAT THINGS WILL REALLY
GET STORMY BY MIDWEEK AS THE REMNANTS OF TYPHOON NIDA COME ONSHORE.
EURO/GFS AND GEM MODELS HAVE BEEN CONSISTENT WITH THIS FOR SEVERAL
DAYS NOW WITH THE TUESDAY NIGHT THROUGH WEDS NIGHT PERIOD LOOKING
VERY UNSETTLED. 8-10 DAY MODEL SOLUTIONS REMAIN VERY WET AND STORMY.

&&

.AVIATION...AS OF 5:15 AM WEDNESDAY...WITH HIGH PRESSURE ALOFT OVER
THE EASTERN PACIFIC AND CENTERED AT THE SURFACE OVER THE GREAT
BASIN...VERY LIGHT PRESSURE GRADIENTS PREVAIL OVER THE CENTRAL
COAST FORECAST AREA THROUGH THURSDAY MORNING. A MOIST LOW-LEVEL WITH
NO OFFSHORE DRYING WIND COMPONENT RESULTING IN FOG DEVELOPMENT IN
THE COASTAL VALLEYS AND OVER THE S.F.BAY WITH ADDITIONAL MOISTURE
FROM THE BAY. STRATUS WITH IFR CIGS ALONG THE COAST WITH IFR CIGS
AND MVFR TO IFR VSBYS ELSEWHERE THROUGH 18Z. TOPS OF THE STRATUS
BETWEEN 12-14 HND FT MSL. CONDITIONS IMPROVING TO MVFR TO VFR VSBYS
LIMITED BY FOG/HAZE UNTIL 20Z...THEN VFR CONDITIONS THROUGH 03Z THIS
EVENING. EXPECT SIMILAR CONDITIONS TO DEVELOP TONIGHT WITH STRATUS
MOVING ONTO THE CENTRAL COAST BY 03Z AND THEN STRATUS/FOG AROUND
S.F.BAY BY 09Z THROUGH THURSDAY MORNING. VARIABLE DIRECTION WINDS AT
OR BELOW 8 KNOTS THEN GENERALLY NW DURING THE AFTERNOON AND EVENING
HOURS.

VICINITY OF KSFO...MVFR TO OCNL IFR VSBY IN FOG WITH IFR CIG TO 18Z
WITH TOPS AROUND 1200 FT MSL. BECOMING MVFR VSBY AND SCT008 TO 19Z
THEN VFR WITH NO RESTRICTION AFTER 19Z THROUGH THE AFTERNOON AND
EVENING HOURS. LIGHT NW WINDS LESS THAN 8 KTS THIS MORNING THEN 6-
10KTS DURING THE AFTERNOON. IFR CIG IN STRATUS RETURNING AFTER 08Z
TONIGHT.

KSFO BRIDGE APPROACH...IFR CIG BKN-OVC002-008 TOPS012 WITH IFR TO
MVFR VSBY CLEARING OVER THE BAY BY 18Z. FEW-SCT008 UNTIL 20Z BUT VFR
WITH NO RESTRICTIONS DURING THE AFTERNOON AND EVENING HOURS. IFR
CIG/MVFR VSBY DUE TO STRATUS/FOG RETURNING AROUND 10Z TONIGHT.

VFR CONDITIONS WITH ONLY SCT-BKN CIRRUS
CLOUDS. VERY SLIGHT CHANCE OF IFR CIGS/VSBYS FORMING NEAR SUNRISE.

MRY BAY AREA TERMINALS...IFR CIGS/MVFR VSBYS WITH MARINE LAYER 1200-
1400 FT MSL...DISSIPATING AROUND 18Z TO VFR CIG/VSBYS AND LIGHT NW
WIND FLOW AT OR BELOW 8 KTS. IFR CIG IN STRATUS RETURNING THIS
EVENING 02-04Z THEN IFR CIG/MVFR VSBY OVERNIGHT. MARINE
LAYER.

&&

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

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: GUDGEL

NWS ON THE WEB AT WEATHER.GOV/SANFRANCISCO