High Surf Advisory 3, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco CA
210 PM PST Thu Feb 27 2025

...New SYNOPSIS, SHORT TERM, LONG TERM...

.SYNOPSIS...
Issued at 209 PM PST Thu Feb 27 2025

One last warm day ahead for Friday before the pattern turns cooler
and unsettled. A storm over the Central Pacific is producing swell
that will arrive along the Pacific coast late Friday and remain
into Monday with sneaker waves and building breakers.

&&

.SHORT TERM...
(This evening through Friday)
Issued at 209 PM PST Thu Feb 27 2025

Afternoon satellite is showing high clouds passing over the area,
streaming off a cutoff low moving towards Southern California.
With this low to our south, surface observations are indicating
offshore flow across the region. These two things combine have had
a field day with the temperatures. Most areas (as of 1 PM) are
running at or near yesterday's temperatures, plus or minus a few
degrees. This is a result of the high clouds being a little more
optically thick than expected. Then there's the coast. The winds
out of the east, on the north side of the cutoff low are causing
downsloping along the coast which are popping temps up rapidly.
Half Moon Bay is in the mid 70s and Monterey in low 80s. This
pattern will continue the rest of the day and into the night,
though temps will cool with lack of sunshine. Models have been
struggling with Friday as the ridge starts to break down, but
holds on for dear life. As such, the spread in model temperatures
is large. The best way to describe it is the north end of our
service area will see temps only a few degrees off from today,
while the southern end will see a larger drop, being closer to the
low. No matter how you shake it, Friday will be the last warm for
a bit.

For full transparency, SPC does have the southern 1/4 of Monterey
County in a general thunder line. From looking into cross
sections, the low level instability seems to be there, steepening
lapse rates, but the moisture is locked into the mid and upper
levels where it is more stable. Thus no moisture to interact with
the instability and therefore near zero chance of thunderstorms.
Fair weather cu? Sure. But not deep convection.

&&

.LONG TERM...
(Friday night through next Wednesday)
Issued at 209 PM PST Thu Feb 27 2025

This is where the forecast gets interesting. The system farther
out sea is lifting into the Gulf of Alaska, but the front
continues to sag well into the tropics. Along the front some
cyclogenesis will develop allowing for a secondary low to form.
This low is expected to track towards the Pacific Northwest with a
triple point low developing farther south. This will impact our
weekend weather with increasing clouds and precipitation spreading
across our service area. As this system bears down Sunday morning,
the trough will take a negative tilt and whip the cold front
through the area. This will provide a focus point for some
convection to fire off. Where? That's a great question. The best
guess at this point is across the Bay Area core, from North Bay
down through South Bay is all potential. This will be more refined
over the next day or so. When? Sunday morning. In terms of weekend
rainfall, expect anywhere from a few hundredths to around a half
inch. This may be refined upward in terrain enhanced areas as the
system comes into hi-res model data time frame.

Beyond the weekend, the storm door is open. Unsettled weather will
continue through the week with a cool air mass in place. Minimum
temperatures Monday and Tuesday mornings will be the coldest,
dipping into the mid 30s for our normal cold spots. The Tuesday
into Wednesday rain may drop a couple inches in terrain favored
areas of the Santa Cruz Mountains and Santa Lucia Range. Details
are still somewhat murky as to exact timing and amount of
precipitation.

&&

.AVIATION...
(18Z TAFS)
Issued at 1038 AM PST Thu Feb 27 2025

Offshore pressure gradients and winds prevail, SAC-SFO is 1.3 mb
and WMC-SFO is 8.9 mb. Easterly winds are resulting in areas of
downsloping warming and drying, this in addition to the thermal
ridging aloft and a lower level temperature inversion is helping
to keep VFR going area-wide. It's a near persistence forecast
today and tonight with exception that model boundary layer humidity
forecasts show increasing coastal low clouds tonight and Friday
morning. Radiative cooling may also contribute to the formation of
patchy valley fog, e.g. KSTS Airport tempo LIFR-IFR forecast Friday
morning.

Vicinity of SFO...VFR. East to southeast wind near 5 knots continuing
through late morning and afternoon. The OAK-SFO pressure gradient is
0.3 mb, supports a mainly light offshore wind. Wind shift to northwest
by early evening, then mainly light and variable tonight and light
northeast wind Friday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Coastal low clouds /IFR-MVFR/ developing
late tonight and Friday morning. Light and variable winds except
southeast 15 to 25 knots KSNS Airport today, winds tonight mainly
light and variable.

&&

.MARINE...
(Today through Tuesday)
Issued at 949 AM PST Thu Feb 27 2025

Light to moderate winds continue over the coastal waters through
the rest of the work week. A moderate northwest swell is building
into the outer waters with a long period west swell arriving
Saturday. Rain likely this weekend to next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PST Friday for Pt Arena to Pt
     Reyes 0-10 nm.

     Small Craft Advisory until 9 PM PST this evening for Pt Reyes to
     Pigeon Pt 0-10 nm.

     Small Craft Advisory from 9 PM this evening to 9 AM PST Friday
     for Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PST Friday for Pigeon Pt to Pt
     Pinos 10-60 NM-Pt Arena to Pt Reyes 10-60 NM.

&&

SHORT TERM...BFG
LONG TERM....BFG
AVIATION...Canepa
MARINE...Canepa

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