Small Craft Advisory 36, NWS San Francisco Bay Area, CA

Area Forecast Discussion
National Weather Service San Francisco CA
945 PM PDT Mon Mar 10 2025

...New AVIATION...

.SYNOPSIS...
Issued at 335 AM PDT Mon Mar 10 2025

An active pattern will begin to ramp up late Tuesday night after a
quiet start to the work week. The first of two relatively weak
Atmospheric River storm systems will bring periods of heavy rain
Wednesday into early Thursday with a slight chance of thunderstorms,
gusty winds, high surf and chances of snow for some elevated areas
above 2500-3000ft. Multiple rounds of rainfall continue Friday
through next weekend.

&&

.UPDATE...
Issued at 841 PM PDT Mon Mar 10 2025

High clouds blanket the region, stemming from the low centered off
Point Conception, with the latest radar imagery showing some light
echoes off the Big Sur coast. The region could see a sprinkle or
two overnight, while the easterly upper level flow should keep
most of the forecast region dry. The forecast focus continues to
be the switch to a more active pattern starting Tuesday night with
multiple rainstorms throughout the extended forecast.

DialH

&&

.SHORT TERM...
Issued at 132 PM PDT Mon Mar 10 2025
(This afternoon through Tuesday)

Beautiful late winter day around the Bay Area and Central Coast
with mostly sunny skies and mild temperatures. If you've been a
discussion reader the last few days it's the proverbial calm
before the storm. If you look at the picturesque visible satellite
imagery we're not talking about the "storm" spinning west of Pt
Conception. That low pressure will bring a few showers to the
southern coastal waters and more widespread rain to SoCal.

Tonight: the surface low to the southwest will track eastward into
SoCal. Behind on the drier northern side of the low will keep most
of the forecast area precip free, but Monterey coast may see a
shower or two or light upslope drizzle.

Tuesday: A transition day in the longwave pattern. The cut-off low
drifts eastward with the subtropical south of that feature.
Farther upstream the polar jet become much more wavy - or highly
amplified. The upstream side of a digging upper trough will be
fueled by a 150+kt jet. The jet structure will promote
cyclogenesis off the PacNW and a stout cold front extending to
the south. By late Tuesday the PacNW surface low is forecast to be
under 1000mb with its cold front inching its way toward the Bay
Area. So what does all of this mean? Clouds will increase through
the day on Tuesday with light rain (warm front/warm sector)
reaching the a majority of the CWA by late Tuesday evening.

&&

.LONG TERM...
Issued at 150 PM PDT Mon Mar 10 2025
(Tuesday night through next Sunday)

Rainfall coverage and intensity will increase through Tuesday
night into Wednesday making for an interesting Wednesday AM
commute. The aforementioned cold front will be knocking on our
doorstep early Wednesday. Latest timing has the cold front sweep
through the region during the day on Wednesday. The fropa will be
aided by upper level support with a cyclonic curvature of the jet
overhead. In other words, broad upper level divergence will
accompany the fropa providing even more lift. Let's talk rain -
the cold front will be able to tap into some higher PWAT air being
advected in from the SW (0.75-1.0"). While it will be a weaker AR
it's not as juicy as some of the systems earlier this season.
Regardless, the frontal dynamics and upper level support will
result in moderate to heavy rain with the fropa. Heaviest rain
will traverse the region N (morning) to S (evening) before
exiting. Additionally, the heavier rain will quickly transition to
showers behind the front with a much more unstable airmass. A low
chance of thunderstorms (15-20%) will be possible Wednesday
evening into Thursday. Given the thermal profile small hail seems
likely even if we don't get actual lightning strikes. Convective
showers will remain through Thursday with a post frontal regime.
Speaking of thermal profile, snow levels look to plummet quickly
with the fropa to 2,500 to 3,000 feet by Thursday. A wet snow will
be possible over the highest peaks in the CWA - up to a half a
foot in the Santa Lucia range. Rainfall amounts 2-4" N Bay Mts and
Coastal Mts and 0.75-1.5" elsewhere. The last piece for precip
with system 1 - flooding potential. The main stem rivers appear to
be OK with no concerns as we're coming into this system drier.
However, rainfall rates maybe high enough with the fropa to lead
to localized ponding on roads and stream rises on flashier
waterways. WPC still has a the region in a Marginal risk for
excessive rainfall on Wednesday.

Aside from precip winds will be an issue with system 1. Southerly
winds will ramp up ahead of and with the fropa late Tuesday and
Wednesday. Winds still look to fall short of a Wind Advisory, but
still very gusty along the coast and higher terrain.

Before more precip arrives, temperatures Thursday night will be
challenging as a lot will depend on cloud cover. Current forecast
is chilly with some 30s across the interior, but if more clearing
occurs temperatures will be colder and more impactful to those
without adequate shelter.

Friday will be an interesting day weatherwise - a fast moving NW
flow aloft with embedded shortwaves will keep precip chances in
the forecast. In fact, guidance has been trending wetter with
these shortwave passages. Therefore, no big break per se before
system 2 arrives over the weekend.

Late Saturday and into Sunday the polar jet becomes highly
amplified once again resulting in another frontal passage. The
overall pattern looks similar to system 1, but not as cold,
convective, or as PWAT rich. Regardless rain Saturday night
through Monday with amounts similar 2-4" N Bay Mts and
Coastal Mts and 0.75-1.5" elsewhere.

6-10 outlook keeps the storm door open with more storms in the
Pacific.

&&

.AVIATION...
(06Z TAFS)
Issued at 945 PM PDT Mon Mar 10 2025

VFR continues area-wide per surface observations. The evening
Oakland upper air sounding showed 0.42" precipitable water which
was a little below early-mid March normal. The sounding showed the
air was saturated near the 500 mb level, however it was much
drier from 18 thousand feet to the ground level. 24 hour trends
show warmer air temps and lower dewpoint temps (less water vapor)
across a fair amount of the forecast area, this supports VFR
forecast tonight and Tuesday. Higher level cloudiness will slow
radiative cooling tonight and Tuesday morning.

Vicinity of SFO...It's a near high confidence VFR forecast for
the 06z TAF. The winds around the terminal will likely become
light and variable tonight and Tuesday morning, with a westerly
wind near 10 knots resuming Tuesday afternoon and evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...It's a near high confidence VFR forecast
for the 06z TAFs. Similar to the Bay Area, conditions aloft and
at the surface are mainly dry. High cloud cover will slow radiative
cooling tonight and Tuesday morning. Winds will become light
southeast tonight and Tuesday morning. Winds becoming west to
northwest near 10 knots Tuesday afternoon then light southeast by
mid Tuesday evening.

&&

.MARINE...
(Tonight through next Sunday)
Issued at 841 PM PDT Mon Mar 10 2025

Winds and seas stay light through late Tuesday night. Hazardous
conditions are expected Wednesday through Friday as gusty winds
and rough seas build into the waters. Widespread rainfall is
expected Wednesday and Friday with a slight chance for
thunderstorms in between systems Wednesday and Thursday. Active
weather looks  to last into the next work week.

&&

.BEACHES...
Issued at 429 PM PDT Mon Mar 10 2025

Moderate period westerly swell arrives along the coastline
Wednesday into Thursday. Expect westerly swell 7 to 9 feet
Wednesday increasing to 10 to 12 feet Wednesday night and
Thursday, with possibly higher breakers near 15 feet Thursday.
We'll continue to monitor beach conditions through mid-week,
including potentially for increasing surf Sunday through Sunday
night.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 PM Tuesday to 9 PM PDT Wednesday for
     Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 AM to 9 PM PDT Wednesday for Pigeon
     Pt to Pt Pinos 10-60 NM.

&&

SHORT TERM...MM
LONG TERM....MM
AVIATION...Canepa
MARINE...Canepa

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