NWS Forecast Area Discussion - San Francisco Area

FXUS66 KMTR 251219

Area Forecast Discussion
National Weather Service San Francisco CA
519 AM PDT Mon Sep 25 2023


Issued at 250 AM PDT Mon Sep 25 2023

Rain is on track to arrive this afternoon across the North Bay.
Cold front will weaken as it moves south, only bringing the SF Bay
Area a few hundredths of an inch of rain through Tuesday morning.
Dry weather returns for the remainder of the week with slight
warming through Thursday. Potential for gusty north to northwest
winds mainly over the coastal waters mid to late week this week.


(Today and tonight)
Issued at 250 AM PDT Mon Sep 25 2023

Rain is on the way! As of writing, KBHX radar in Eureka shows
rain starting to move across NW California. The cold front is
currently just offshore the CA/OR border which will move
southeastward through the day today and reach the North Bay by the
evening. The North Bay could start to see some warm sector light
rain as early as later this morning. The main rain will arrive
this afternoon/evening as the weakening cold front approaches.

QPF has not changed much as we are still expecting most of the
rain to remain north of the Golden Gate. Amounts are still looking
like 0.15-0.5" across the North Bay west of the Mayacamas.
Favored coastal terrain in Sonoma County (ie SW-facing) will be on
the upper limit of that range. Places like Napa, the SF
Peninsula, Oakland, and the Santa Cruz Mountains are expected to
get a few hundredths of an inch late tonight into Tues morning.
Upper level support and surface cold front subsequently will
weaken as it moves south into the Bay Area, hence why those areas
will see very little rain if any at all.

In addition to rain chances, southerly winds will strengthen ahead
of incoming cold front. Widespread gusty conditions not expected,
but more localized breezy to gusty conditions likely across higher
terrain and mountain passes (such as Altamont Pass) this


(Tuesday through Sunday)
Issued at 250 AM PDT Mon Sep 25 2023

Besides some lingering drizzle Tuesday morning, dry conditions
resume Tuesday. Despite the cold front having passed, a large NW
swell that originated from this powerful low over the NE Pacific
will propagate through the coastal waters. A High Surf Advisory is
in effect for the Pacific coastline for most of the day Tuesday, so
use caution and stay aware of surroundings if planning to go to the
beach. Large breaking waves may be hazardous to beach-goers,
especially for NW facing beaches.

Tuesday through Thursday will feature a subtle warming and drying
trend with temperatures reaching seasonal norms. By Wed, a
shortwave trough will eject from the upper low off the Gulf of
Alaska will into the Pacific NW, which may bring more rain to
NorCal. However, the North Bay likely won`t see any additional

By the weekend, the upper trough over the Pacific NW will become
more amplified and dig into the Great Basin. We`re keeping an eye
on the track of this low, whose position may support offshore
flow this weekend, particularly for the interior N Bay Mtns and
the Diablo Range. There`s uncertainty in how it will play out
still. 6 and 7 day cluster analysis show there are differences
among ensemble members regarding the trough axis location as well
as strength of the trough, highlighting the uncertainty. We will
continue to monitor closely as it may result in elevated fire
weather conditions this weekend.


(12Z TAFS)
Issued at 507 AM PDT Mon Sep 25 2023

A look at current satellite imagery shows high clouds beginning to
push into the northern portion of the region, and very sparse
stratus coverage.As a result of sparse stratus coverage, many
terminals are reporting VFR conditions, and are expected to remain
so through at least the evening of tonight, though high clouds
will still be present through the day. North bay terminals are
likely to see MVFR CIGS develop towards the mid evening as rain
showers approach the area. Elsewhere, MVFR CIGS build in towards
the early morning hours of Tuesday and last through the late
morning. Winds have begun to turn southerly, though remain light
as of this writing. However, expect winds to gradually increase
through the day to become breezy to moderate around 12 knots
generally, locally gusty near coastal gaps, and developing a more
SW component into the afternoon. Into the late evening, winds ease
and turn to become onshore in the morning of Tuesday.

Vicinity of SFO... VFR conditions continue through much of the
day though high clouds begin to build in. Winds have begun to
develop a S component, and are expected to increase in strength to
around 8-10 knots. Into the afternoon hours, winds increase to
become breezy near 12 knots and slowly become more SW as opposed
to S. Into Monday night, SW winds become S once more as they ease
to become light overnight. Towards the early morning of Tuesday,
MVFR CIGS develop just as precipitation chances begin, with light
drizzle to rain possible.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Currently VFR with just a few high clouds
passing over. VFR lasts through the late night tonight, though
high clouds build in to become SCT. Winds increase to around 12
knots out of the W/SW this afternoon before easing into the night.
Late return of stratus and MVFR CIGS expected, near the end of
the TAF period.


(Tonight through next Friday)
Issued at 835 PM PDT Sun Sep 24 2023

Gentle to moderate southerly winds and moderate sea heights are
observed throughout the coastal waters at the moment. In the
northern waters, winds will increase to a fresh to strong
southerly breeze with occasional gale force gusts possible early
Mon. A storm force low off the coast of the PNW is generating
high seas in the NE Pacific. These seas will enter the coastal
waters Mon as a moderate to high NW swell. The worst conditions
will be Tuesday with 12-15 ft seas in a 15 second NW swell. A
small craft advisory is in effect for all unprotected waters.


Issued at 507 AM PDT Mon Sep 25 2023

A high surf advisory is in effect from 5am to 11pm Tuesday due to
large breaking waves generally around 12 to 16 feet, with locally
higher conditions around 15 to 20 feet at steep-sloped beaches.
Northwest facing beaches are most at risk for these hazardous

These large breaking waves are generated by large
northwesterly swell resultant from an approaching storm.
Conditions at beaches will be dangerous for swimmers, surfers,
and beachgoers. If planning to visit a beach, caution is advised,
as large waves can sweep across beaches with no warning, pulling
people into the ocean from jetties, beaches, and rocks. Remember
to never turn your back on the ocean, and check local conditions
such as tides and currents before visiting.

Exercise caution even after the high surf advisory has ended, as
energy in the ocean can be slow to diminish and large waves may
continue to be present afterwards until fully dissipated.


CA...High Surf Advisory from 5 AM to 11 PM PDT Tuesday for CAZ006-505-

PZ...Small Craft Advisory until 3 AM PDT Wednesday for PZZ540.

     Small Craft Advisory from 9 AM Tuesday to 3 AM PDT Wednesday for

     Gale Warning until 3 PM PDT this afternoon for PZZ570.

     Small Craft Advisory from 9 PM this evening to 3 AM PDT
     Wednesday for PZZ575.



LONG TERM....McCorkle

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NWS MTR Office Area Forecast Discussion