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

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FXUS66 KMTR 271828
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
1028 AM PST Fri Jan 27 2023

.SYNOPSIS...Mild temperatures through tomorrow but cooler over
the weekend. A weak cold front passes over Sunday into Monday
morning bringing light right and minimal accumulations. Behind the
front will be colder air that will make for chilly morning low
temperatures early next week, with a widespread freeze likely away
from the coast, and even touching some coastal areas.

&&

.DISCUSSION...as of 07:25 AM PST Friday...

Fog has developed over the North Bay Valleys and around the Bays.
Updated the forecast to include a Marine Dense Fog Advisory for SF
and San Pablo Bays and a Special Weather Statement for localized
lower visibility in spots. Please travel carefully this morning
and watch for sudden visibility changes.

&&

.PREV DISCUSSION...as of 03:40 AM PST Thursday...What a difference 24
hours makes. Yesterday there was a decent offshore flow gradient
between SFO-WMC leading to gusty offshore flow winds, clear skies,
and very mild overnight lows. That noted offshore flow is pretty
much non-existent tonight. As a result, winds are much weaker
(valley locations are calm), stratus has returned to the coastal
waters/locally inland, and temperatures have plummeted. Last
night temperatures in the North Bay were in the 50s and 60s, but
tonight they`ve dropped into the 30s. KSTS for instance is 25
degrees colder, KAPC is 21 degrees colder, and KOAK is 17 degrees
colder. There are also reports of patchy fog impacting the North
Bay Valleys with Petaluma showing dense fog at 1/2 mile.

For today and tonight: Morning low clouds/fog will dissipate by
mid-late morning. Today will feature a few clouds and mild
temperatures with highs in the upper 50s to lower 60s. Friday
night will see additional clouds ahead of a weak front, but lows
will remain chilly and in the 30s to lower 40s.

Sunday: A weak cold front is still on track to gradually move
through the region. This fropa will bring a chance for showers
for areas mainly south of San Jose. Rainfall amounts will
generally be light and less 0.25". The fropa will drop snow levels
to less than 3500 feet. In fact, the NBM drops snow levels to
less than 2900 feet Sunday afternoon. Therefore, it looks like a
low snow level and low qpf set up. Current forecast does have some
accumulating snow over the Santa Lucia and S Gabilan ranges, but
only a coating to two inches. Any lingering precip ends by Sunday
evening. Temperatures on Sunday will struggle to hit the mid 50s
most areas and the hills/mts remain in the 30s/40s.

Sunday night into next week: Once the precip chances end the
bigger impact will turn toward cold temperatures, mainly at night
with widespread 30s. Sunday night and Monday night will features
widespread 30s, but interior valleys will be near freezing or in
the upper 20s. Not expecting a big warm up during the day either
with highs staying in the 50s. If this trend continues a Freeze
Warning will likely be need later this weekend valid for Sunday
night at the earliest. Biggest impacts would be to those without
adequate shelter.

Temperatures will gradually warm Wednesday into Thursday as clouds
increase ahead of an approaching storm system. Widespread rain
chances are back in the forecast by next Thursday night/Friday as
a storm system moves through the region. Longer range guidance
shows some rain, but a far cry from all of the ARs that recently
impacted CA. In fact, latest AR guidance doesn`t even give the
system enough moisture to push it into a weak AR.  Stay tuned...

&&

.AVIATION...as of 10:00 AM PST Friday...For the 18Z TAFs. Marine
stratus that meandered to the SF Bay early this morning via the
Golden Gate still remains in a few spots but looks to dissipate by
20Z. VFR expected after 20z. Breezy onshore flow of 8 to 12 knots
in the afternoon with locally breezier winds near coastal gaps.
Around 06Z tomorrow, a push of marine stratus into the SF and
Monterey bays brings with it MVFR-IFR conditions lasting through
the early morning.


Vicinity of KSFO... VFR after 20z with increasing NW winds this
afternoon and evening, potentially up to 12kts. Winds dissipate
and calm overnight as the marine stratus pushes inward, reducing
visibilities to possible IFR conditions in the early morning
hours, around 6z, then looking to improve to VFR late morning
tomorrow.

KSFO Bridge Approach...Low clouds are currently impacting the
approach.

Monterey Bay...VFR through the evening today. Winds will shift
onshore this afternoon. Low clouds move in this evening and will
linger overnight into the early morning tomorrow, potentially
bringing IFR conditions. After 16z, VFR conditions return.

&&

.MARINE...as of 09:56 AM PST Friday...Long period northwesterly
swell has arrived and will continue  through the weekend, slowly
diminishing. Winds will begin to  increase late this morning into
the afternoon, creating hazardous  conditions for small craft.
Locally gusty winds with occasional  low end gale force gusts
possible this evening over the northern  waters. Light rain is in
the forecast for Sunday as a weak cold  front pass over the
waters.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tday...Marine Fog Advisory...SF Bay until 10 AM
             SCA...Pt Arena to Pt Reyes 0-10 nm from 3 PM
             SCA...Pt Reyes to Pigeon Pt 0-10 nm from 3 PM
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm from 3 PM

&&

$$

PUBLIC FORECAST: MM/SPM
AVIATION: AC
MARINE: SPM

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