Small Craft Advisory 7, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco Bay Area
957 PM PST Wed Jan 8 2020

.SYNOPSIS...Clouds increase this evening with rain developing
after midnight in the North Bay. Rain spreads southward impacting
the Bay Area commute Thursday morning with most rain ending before
lunchtime Thursday. Clear and cold Thursday night into Friday
morning with widespread 30s. Dry but cool on Friday. Next weak
front arrives Saturday morning with spotty light rainfall. Dry but
cool Saturday afternoon through Sunday. Cool and showery pattern
early next week could turn more stormy by late next week.

&&

.DISCUSSION...as of 1:55 PM PST Wednesday...Its a cool January
day where the sun has yet to come out with 1 pm temps still in the
upper 40s to around 50 while areas seeing the sunshine have
warmed into the mid/upper 50s. Forecast focus is quickly turning
to incoming weather system. High clouds are already racing towards
Cape Mendocino in advance of this incoming upper level shortwave.
Models are consistent in showing steady rain band developing over
Sonoma County sometime after midnight. Model cross sections
showing 130-150 kt jet streak taking aim towards the Bay Area
early Thursday morning with strong N/NW winds through the
troposphere. This will drive the surface cold front rapidly
through the region during the early morning hours of Thursday.
Roughly from 12-15z for the North Bay and Bay Area and 15-18z for
the Central Coast. Some brief northwest wind gusts will likely
cause havoc along with brief heavy downpours as the front races
through during the early morning commute. Most places should be
able to pick-up a quick quarter inch or so with up to a half inch
in the hills. The speed of the system will be a limiting factor
for higher rainfall totals. Snow levels should stay above 4500
feet.

Behind the front there will be clearing but blustery nw winds
Thursday afternoon. Its not an ideal set-up but a quick shot of
cold air will settle over the region Thursday night into Friday
morning with lows in the 30s most areas except the City and coast.
Winds dont die off and lingering clouds/fog will be limiting
factors for widespread frost Friday morning.

Dry but cool Friday as the King Tides arrive. Next weak front
moves through Saturday morning. QPF looks very light with this
front as it falls apart south of Santa Cruz. Rain totals for
Saturday morning look to be around a tenth, just enough to mess
up Saturday morning outdoor plans. Drying trend Saturday afternoon
through Sunday for weekend activities.

Long range remains unsettled with weak systems bringing rain
chances later Monday through Weds. Possibility of a stronger storm
later next week but models still waffling on details.
Teleconnections favor a negative PNA. For the next week or so any
rains look light and beneficial before heavier rain chances in the
extended.

&&

.AVIATION...as of 9:55 PM PST Wednesday...A mix of lower and mid
clouds early this evening. Cigs around the Bay Area have been
around 5000 ft but will lower to 3000 ft or below after 09Z as a
frontal system arrives bringing some light rain. Winds will switch
to southwest 5-10 kt as the front arrives then become northwest
15-20 kt behind the front. Rain moves out of the area Thursday
morning and cigs will rise. Models keep low- level moisture in
through 18-20Z Thursday with afternoon convection keeping sct-bkn
cumulus clouds. Should be mostly clear Thursday evening.

Vicinity of KSFO...Becoming MVFR cigs lowering to 2500 to 3000 ft
after 09Z with light rain. Rising cigs after 16Z then scattering
out after 20Z. Winds becoming southwest 10 to 15 kt then switching
to northwest after frontal passage.

SFO Bridge Approach...Similar to KSFO.

Monterey Bay Terminals...MVFR cigs developing. Vsbys lowering to
4 to 6 miles in light rain 12Z-18Z. Clearing after 22Z.

&&

.MARINE...as of 09:29 PM PST Wednesday...A frontal system will
move through the waters tonight accompanied by light rain.
Northwest winds will increase Thursday after the front passes.
Winds will slowly decrease on Friday but may increase again
Saturday after another front moves through. A large long-period
northwest swell will arrive this weekend.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm from 3 AM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Arena to Pt Reyes 0-10 nm from 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 AM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 AM
             SCA...SF Bay from 3 AM

&&

PUBLIC FORECAST: RWW
AVIATION: W Pi
MARINE: W Pi

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