Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA

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000
FXUS66 KMTR 261123
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
323 AM PST WED NOV 26 2014

.SYNOPSIS...HIGH PRESSURE WILL BRING DRY WEATHER WEDNESDAY AND
THURSDAY WITH CONTINUED SEASONABLY WARM AFTERNOONS. BY FRIDAY
CLOUDS WILL BEGIN TO INCREASE AHEAD OF THE NEXT WEATHER SYSTEM.
LIGHT RAIN IS FORECAST TO BEGIN IN THE NORTH BAY FRIDAY NIGHT AND
THEN SLIDE SOUTHWARD THROUGH THE REST OF THE BAY AREA AND CENTRAL
COAST SATURDAY INTO SUNDAY. THE MAIN FRONTAL PASSAGE WILL THEN
OCCUR SOMETIME MONDAY WHEN HEAVIER RAIN AND STRONGER WINDS ARE
EXPECTED. SHOWERS WILL LIKELY LINGER THROUGH TUESDAY BEFORE DRYING
TREND RETURNS BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...AS OF 3:23 AM PST WEDNESDAY...THE SHORT TERM
FORECAST REMAINS ON TRACK. SKIES ARE MOSTLY CLEAR AGAIN THIS
MORNING WITH ONLY SOME PATCHY FOG BEING REPORTED AT SANTA ROSA AND
CONCORD. TEMPERATURES AND DEW-POINTS ARE TRENDING SLIGHTLY HIGHER
THAN 24 HOURS AGO WHILE WE STILL HAVE OFFSHORE GRADIENTS FROM SFO
TO WMC AND SFO TO SAC. UPSHOT IS ANOTHER SUNNY AND MILD DAY IN
STORE WITH AFTERNOON HIGHS IN THE UPPER 60S FOR MOST OF THE BAY
AREA WITH 70S FOR THE SANTA CLARA VALLEY AND MONTEREY BAY REGION.
FOR ONCE KSFO WONT BE CONTRIBUTING TO AIRPORT DELAYS ACROSS THE
COUNTRY WITH NO CONCERN FOR LOW CLOUDS/FOG TODAY. HOWEVER WEATHER
BACK EAST WILL CREATE PLENTY OF AIR TRAVEL DELAYS. THOSE TRAVELING
BY CAR ACROSS CALIFORNIA SHOULD ENCOUNTER NO WEATHER DELAYS WITH
NO PRECIP OR FOG TO WORRY ABOUT.

THANKSGIVING WEATHER LOOKS PLEASANT WITH HIGH PRESSURE STILL IN
CONTROL. WINDS MAY TURN MORE WESTERLY BY AFTERNOON WITH PERHAPS A
FEW HIGH CLOUDS BUT HIGHS STILL COMFORTABLY IN THE 60S BAY AREA
AND SOME 70S FOR THE CENTRAL COAST.

AS HAS BEEN THE CASE THE LAST SEVERAL DAYS WERE STILL FOCUSED ON
THE WEEKEND WEATHER EVENT. SOME OF THE DETAILS ARE BECOMING MORE
CLEARLY DEFINED IN TERMS OF HOW THE MODELS ARE HANDLING THE
VARIOUS FEATURES OVER THE PACIFIC. TO CUT TO THE CHASE THE BIG
DEVELOPMENT OVERNIGHT HAS BEEN THE 00Z ECMWF DRAMATICALLY SLOWING
THE MAIN COLD FRONTAL PASSAGE. WILL NEED TO SEE IF THIS IS AN
OUTLIER BUT THE GEM AND GFS MODELS HAVE ALSO TRENDED SLOWER.

STILL LOOKS LIKE LIGHT RAIN DEVELOPS IN THE NORTH BAY FRIDAY NIGHT
BUT STAYS NORTH OF THE GOLDEN GATE. THEN ON SATURDAY THAT BOUNDARY
WILL DROP SOUTHWARD THROUGH THE BAY AREA AND INTO THE MONTEREY BAY
REGION. IT WILL BE A WARM ADVECTION RAIN THAT HAS ORIGINS TO A
TONGUE OF HIGH PRECIPITABLE WATER VALUES TRACING ALL THE WAY
TOWARDS HAWAII. PWAT VALUES AROUND 1.25 INCHES GET POINTED INTO
THE SANTA CRUZ MOUNTAINS ON SATURDAY IN A NARROW ATMOSPHERIC RIVER
SET-UP. FOR THOSE FOLLOWING ALONG AT HOME ITS THE BAND OF MOISTURE
CURRENTLY OUT NEAR 35N/138W THAT WILL EVENTUALLY GET POINTED
PERPENDICULAR TO OUR COASTAL RANGES. ITS CONCEIVABLE THAT IT MAY
END UP OVER THE NORTH BAY ON SATURDAY OR AS FAR SOUTH AS THE SANTA
CRUZ MOUNTAINS. THIS COULD SET THE STAGE FOR SOME PRETTY DISPARATE
RAIN TOTALS WITH THE INITIAL SYSTEM WHERE SEVERAL INCHES COULD
FALL IN THE SANTA CRUZ MOUNTAINS WITH MUCH LIGHTER AMOUNTS FOR THE
BAY AREA VALLEYS.

THAT BOUNDARY WILL KIND OF WASH OUT LATER SATURDAY NIGHT INTO
SUNDAY AS THE PARENT LOW WELL OFFSHORE STARTS TO DIG. THE END
RESULT SHOULD BE CONTINUED PERIODS OF MAINLY LIGHT RAIN ACROSS
MOST OF THE DISTRICT ON SUNDAY. HOWEVER WITH NO STRONG DYNAMICS OR
FORCING NOT SEEING A HEAVY RAIN EVENT FOR SUNDAY...FURTHERMORE THE
FLOW WILL TURN MORE SOUTHERLY WHICH CAN SHUT DOWN OROGRAPHICS FOR
MOST LOCATIONS.

FOR THE LAST FEW DAYS THE MODELS WERE INDICATING SUNDAY NIGHT OR
EARLY MONDAY IS WHEN THE WORST WEATHER WOULD OCCUR AS THE PARENT
LOW AND SURFACE FRONT MOVED ONSHORE. THAT TIMING COULD HAVE BEEN
PARTICULARLY BAD FOR RETURN TRAVEL OF THE HOLIDAY WEEKEND. THE
00Z ECMWF CAME IN AROUND 11 PM LAST NIGHT WITH A SHARPLY DIFFERENT
SOLUTION THAT SLOWED THE PARENT LOW BY 24-48 HOURS...NOT BRINGING
THE MAIN LOW ONSHORE UNTIL WEDS MORNING! THAT SEEMS A LITTLE
SUSPECT BUT THE GEM AND GFS HAVE CLEARLY SLOWED THE TIMING OF THE
MAIN FRONT AS WELL. ONCE AGAIN WILL WANT TO SEE THE 12Z CYCLE TO
SEE IF THE ECMWF WAS AN OUTLIER OR TREND SETTER. FOR WHAT ITS
WORTH THE 06Z GFS HAS THE WETTEST CONDITIONS FROM 18Z MONDAY TO
00Z TUESDAY. SO INSTEAD OF IMPACTING SUNDAY NIGHT ITS NOW MORE
INTO THE MONDAY AFTERNOON COMMUTE.

SO WILL EXPECT THE TIMING TO KEEP BEING ALTERED. GOOD NEWS IS RAIN
STILL APPEARS TO BE ON TRACK. HOWEVER ITS SOMEWHAT DISCONCERTING
TO SEE THE ECMWF SOLUTIONS WHICH CUTS THE SYSTEM OFF FROM THE MAIN
JET SOMEWHAT. COMPLICATING FACTORS MORE IS THERE DOES APPEAR TO
BE A TAP INTO SOME SUB-TROPICAL MOISTURE. THE MODELS HAD BEEN VERY
CONSISTENT FOR ABOUT 3 DAYS SO THIS IS A LITTLE BIT OF A KINK IN
THE PLAN AND JUSTIFIES KEEPING POPS IN TH CHANCE CATEGORY FOR MUCH
OF THE EXTENDED UNTIL DETAILS GET SORTED OUT.

&&

.AVIATION...AS OF 9:54 PM PST TUESDAY...VFR IS FORECAST FOR THE
PERIOD EXCEPT KSTS MAY SEE FOG EARLY WED MORNING. LIGHT WINDS.

VICINITY OF KSFO...VFR.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...VFR.

&&

.MARINE...AS OF 09:45 AM PST TUESDAY...HIGH PRESSURE WILL MOVE
INTO THE GREAT BASIN TONIGHT. WINDS WILL BECOME LIGHT EAST TO
SOUTHEAST BY WEDNESDAY AS A FRONTAL SYSTEM MOVES INTO THE PACIFIC
NORTHWEST. SOUTHERLY WINDS WILL INCREASE BY THE END OF THE WEEK AS
A STRONGER STORM APPROACHES THE AREA.

&&

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

$$

PUBLIC FORECAST: RWW
AVIATION/MARINE: CANEPA

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