Frost Advisory 20, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco CA
934 PM PST Thu Nov 23 2023

...New UPDATE, AVIATION, MARINE, BEACHES...

.SYNOPSIS...
Issued at 1132 PM PST Wed Nov 22 2023

Dry and mild today. Breezy winds develop in the hills tonight into
Friday. Cold overnight readings for Friday and Saturday morning
with frost and freezing conditions likely in the coldest interior
valleys.

&&

.UPDATE...
Issued at 932 PM PST Thu Nov 23 2023

A Beach Hazards Statement has been issued for late Friday through
Sunday for sneaker waves (see BEACHES section for more details).
Additionally, minor coastal flooding may occur in San Francisco and
Marin counties due to higher astronomical tides resulting in greater
beach runup this weekend.

Minor changes were made to the forecast this evening, such as
bumping up wind gusts across the N Bay Mtns, including for Mt. St
Helena which was bumped up to 55 mph to account for the higher wind
gusts currently being observed. Windier conditions will continue in
the hills overnight before weakening tomorrow and Saturday. In
addition, a frost advisory will go into effect for interior portions
of the Central Coast from 4AM to 10AM on Friday.

&&

.SHORT TERM...
(This evening through Friday)
Issued at 115 PM PST Thu Nov 23 2023

A few clouds continue to hug the Monterey Peninsula and Big Sur
coast, but they are gradually thinning as the decaying front
moves through. Expect this trend to continue this
afternoon/evening. Elsewhere, wall to wall sunshine blankets the
region with mild temperatures. Not a bad afternoon for a holiday,
especially if you're traveling or spending some time outdoors.

Tonight through Friday: An upper level low will deepen over the
Great Basin. At the surface however, high pressure will build
over OR/WA/NorCal/NV with lower pressure along the CA coast. This
surface pressure setup/orientation will allow for offshore flow.
The SFO-WMC and RDD-SAC are both trending in the direction that
promotes northerly/offshore flow. The gradients max out later
tonight/early Friday with gusty winds over the North and East Bay
higher terrain, but it won't be strong enough to warrant a wind
advisory. That being said, still looking for 35-50 mph above 2500
feet. Mt St Helena could see a gust over 50 mph by Friday
morning. The offshore flow will also usher in drier air limiting
any stratus/low clouds like we had near Monterey Thursday morning.
Outside of windy areas, conditions will be ideal for colder
overnight lows. This will be most notable across interior
Monterey/San Benito counties initially. A Frost Advisory remains
in effect as temperatures drop below 36 degrees tonight.

Despite offshore flow and some sunshine on Friday, temperatures
will actually drop a few degrees as cooler air moves in from the
north. Highs on Friday will be closer seasonal average and in the
upper 50s to 60s.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 145 PM PST Thu Nov 23 2023

Offshore eases by Friday night, but still remains offshore flow
with mostly clear skies. Clear skies and lighter winds will set
the stage for an even colder night. A Freeze Watch remains for
interior Monterey/San Benito where lows plummet to the upper 20s
to low 30s. This will likely need to be converted with the next
forecast package to a Freeze Warning. A Frost Advisory will also
likely be needed for the North Bay Valleys as temperatures drop
below 36 degrees. Elsewhere will be chilly with lows in the mid
30s to mid 40s. Saturday night into Sunday morning looks cold as
well so frost/freeze products may be needed again for the North
Bay Valleys and interior Monterey/San Benito. Given that this
will be a multi-day cold snap at night think of people, pets, and
pipes. Not a lot of change in the overall sensible weather
heading into next week with seasonable daytime temperatures and
chilly overnights.

Still looks like the storm door begins to open at the end of the
month and remains open into December. Current forecast does bring
some showers back to the region the middle of next week.

&&

.AVIATION...
(06Z TAFS)
Issued at 932 PM PST Thu Nov 23 2023

VFR throughout the region and TAF period. Light winds predominate
for now, but the northern half of the region could see winds
building as a northerly gradient builds. Main forecast question is
if the high winds seen aloft mix down to the surface tonight. LLWS
concerns are present tonight across the North Bay, and to a lesser
extent in the East Bay, where wind shear magnitudes are not intense
enough to include in the TAFs. In the southern half of the region,
winds remain a light offshore flow across the Central Coast. North
to northwest flow resumes on Friday afternoon, diminishing in the
evening hours.

Vicinity of SFO...VFR through the TAF period. Rather surprising sea
breeze lingers, but is expected to turn northeasterly later tonight.
Northwest flow returns Friday afternoon and turns northeast later
that evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Nearly high confidence in VFR through the
TAF period. Light offshore flow persists through Friday afternoon,
when northwest flow returns.

&&

.MARINE...
(Tonight through next Tuesday)
Issued at 932 PM PST Thu Nov 23 2023

Hazardous seas conditions continue with steep wind waves and a
building northwest swell. Gale force gusts will begin to diminish
across the northern outer waters tonight, so wind waves will
slowly diminish through tomorrow. Breezy to gusty northerly winds
are possible near the Golden Gate Bridge late tonight into the
early morning Friday. Incoming northwest swells will keep seas
elevated and hazardous for small craft vessels through the
weekend.

&&

.BEACHES...
Issued at 932 PM PST Thu Nov 23 2023

A long period northwest swell of 19 to 21 seconds will propagate
through the coastal waters beginning late tomorrow (Friday),
resulting in an increased risk of sneaker waves especially for
northwest-facing beaches. As such, a Beach Hazards Statement is in
effect for the entire coastline from Sonoma County down to Monterey
County beginning at 10 PM Friday lasting through 8 AM Sunday.
Sneaker wave risk diminishes by Sunday afternoon as swell period
decreases, but the waters may still be turbulent with larger
breaking waves, so caution is still advised. In addition to the
increased sneaker wave risk beginning Friday, high astronomical
tides are expected this weekend, which may bring runup farther along
the beach. Beachgoers and tide poolers should use caution and watch
out for unexpected waves that can sweep you off your feet.

&&

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

     Frost Advisory from 4 AM to 10 AM PST Friday for CAZ516-518.

     Freeze Watch from Friday evening through Saturday morning for
     CAZ516-518.

PZ...Small Craft Advisory until 9 AM PST Friday for PZZ530.

     Small Craft Advisory until 3 AM PST Friday for PZZ540-565.

     Gale Warning until 9 AM PST Friday for PZZ570.

     Small Craft Advisory until 3 PM PST Friday for PZZ575.

&&

UPDATE...Kennedy
SHORT TERM...MM
LONG TERM....MM
AVIATION...DialH
MARINE...McCorkle
BEACHES...McCorkle

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