847
FXUS66 KMTR 181245
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
445 AM PST Sat Jan 18 2025

...New BEACHES...

.SYNOPSIS...
Issued at 415 AM PST Sat Jan 18 2025

Cool weather continues with coastal and valley fog to return again
tonight. A Frost Advisory remains in effect until 9 AM this morning
for portions of the interior Central Coast. Gusty offshore winds
remain likely Monday into Tuesday with peak gusts between 35 to 40
mph across the interior North Bay Mountains.

&&

.SHORT TERM...
(Today and tonight)
Issued at 415 AM PST Sat Jan 18 2025

Satellite imagery this morning shows a blanket of stratus over much
of the Bay Area and Central Coast. There is some clearing along
Marin and the San Francisco Peninsula where weak onshore flow has
developed. Elsewhere, there`s still some expansion of the stratus
which can be seen clearly in the valleys of Monterey, San Benito,
and Napa valleys. Stratus will eventually give way to sunshine by
this afternoon. There`s some conflicting data about what happens
tonight in terms of the stratus. Some guidance suggests we could see
some stratus develop in the North Bay, around San Francisco, and
then around Monterey Bay while other areas remain mostly clear
making the temperature forecast tricky. Should we get our nighttime
blanket of clouds, temperatures would end up warmer than forecasted
in those regions. Will need to re-evaluate low temperatures for
those areas on the dayshift as confidence has lowered in the whether
or not they`ll reach Frost Advisory Criteria. For East Bay, South
Bay, and the Salinas valleys and San Benito County, confidence is
higher in cold overnight temperatures. Frost and/or freeze products
remain possible for these areas.

&&

.LONG TERM...
(Sunday through Friday)
Issued at 415 AM PST Sat Jan 18 2025

Ensembles remain in agreement with an upper level trough holding
over much of the central United States, with an embedded shortwave
trough sliding through the Great Basin and into the Desert Southwest
Monday into Tuesday. Confidence remains high that we`ll have an
offshore wind event; however, confidence remains on low on the
magnitude of it. Ensemble pressure gradient forecasts range from -
11mb to just shy of -16mb from the 0Z runs, with deterministic runs
within that range as well from SFO to WMC. The signal remains best
over the North Bay mountains, where gusts of 30-40 mph remain
possible, perhaps up to 50 mph for higher elevations. The East Bay
and Santa Cruz mountains could be gusty as well, but perhaps
confined to 20-35 mph. Thankfully fire weather concerns remain low
due to early winter rains moistening fuels.

As we head into midweek, cluster analysis shows upper level ridging
returning to the forecast. Daytime temperatures will increase by a
few degrees each day, warming back into the 60s for much of the
region, perhaps to near 70 for South Bay Valleys and the Central
Coast Valleys. Chilly morning lows stick with us, with the mid 30s
to low 40s expected for most regions. Lower temperatures may be
possible in the Southern Salinas Valley.

&&

.AVIATION...
(12Z TAFS)
Issued at 415 AM PST Sat Jan 18 2025

Currently seeing a mixed bag of LIFR-MVFR across the board, high
confidence in VFR by this afternoon. A cutoff low off the coast is
allowing for a relatively deep marine layer of 2,000 feet. As this
cutoff low gets absorbed into the upper-level pattern, the
expectation is that the marine layer will compress. As it does so,
ceilings and visibilities will likely lower to the LIFR-IFR range.
There is a strong signal for fog developing Saturday night with the
HREF showing a 50-75% chance for visibility less than 3 miles and
ceilings less than 1,000 feet.

Vicinity of SFO...Currently MVFR with light southerly flow. Winds
will back through the morning, becoming westerly with the afternoon
sea breeze. High confidence in VFR by this afternoon with sub-VFR
conditions returning overnight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently MVFR with easterly flow at MRY
and MVFR with drainage flow at SNS. Downsloping (warming and drying)
winds will likely allow for MRY to reach VFR before SNS, either way
high confidence in VFR by the afternoon for both terminals. A return
to MVFR conditions is expected tonight.

&&

.MARINE...
(Today through Thursday)
Issued at 415 AM PST Sat Jan 18 2025

Moderate seas and moderate northwesterly breezes will prevail
through the weekend with high pressure continuing to support dry
conditions and fog/low clouds during the overnight periods.
Moderate  offshore breezes next week will limit fog/low cloud
development.

&&

.BEACHES...
Issued at 432 AM PST Sat Jan 18 2025

A long period westerly swell with a period up to 22 seconds will
result in a moderate to high risk of sneaker waves and bring an
increased risk of rip currents beginning today and lingering
through Monday. For beachgoers to remain safe it is vital to keep
off of jetties and rocks, keep pets on a leash, observe the ocean
for 20 minutes before recreating on the beach or in the water, and
never turn your back on the ocean. A Beach Hazards Statement has
been issued for all Pacific Coast beaches from 7 PM today through
7 PM Monday.

Sarment

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from this evening through Monday evening
     for CAZ006-505-509-529-530.

     Frost Advisory until 9 AM PST this morning for CAZ516>518.

PZ...None.
&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Sarment
MARINE...Sarment

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