297
FXUS66 KMTR 130438
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
938 PM PDT Sun Oct 12 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 215 PM PDT Sun Oct 12 2025

 - Widespread rainfall and isolated thunderstorms Monday and Tuesday

 - Heaviest rainfall is likely across the Central Coast

 - Warming and drying trend kicks off Wednesday

&&

.UPDATE...
Issued at 839 PM PDT Sun Oct 12 2025

It is the proverbial calm before the storm... Satellite imagery is
showing a band of mid- to high level clouds over the Bay Area, with
areas of stratus coverage across the southern reaches of San Mateo
County and the higher elevations surrounding Monterey Bay. The 00Z
(5 PM) OAK radiosonde reported a precipitable water value of 0.45
inches. This almost certainly will not be close to what it reports
that time tomorrow. The culprit is an unassuming swirl of clouds
being picked up in the western half of Washington State, revolving
around a broad area of rotation stretching from the Seattle
metropolitan area across the Olympic Peninsula to the Pacific coast.
Over the next 24 hours, this broad rotation is expected to
consolidate itself, travel down the coast through the state, and
bring us a very notable early season rainstorm through Monday with
lingering showers through Tuesday. The cold core of the low will
also enhance the thunderstorm chances with the frontal passage, with
the SPC placing the Bay Area and Central Coast under a general risk
for thunderstorms through the next couple of days.

The forecast remains unchanged. The operations team will continue to
monitor the progress of the low pressure system through the night
and will keep watch of the evolving conditions tomorrow.

DialH

&&

.SHORT TERM...
Issued at 215 PM PDT Sun Oct 12 2025
(This evening through Monday)

Yet another beautiful afternoon across the region with sunny skies
and temperatures warming into the low to mid 60`s near the coast and
lower 70`s across the interior. Breezy conditions are occuring near
the coast and in the higher elevations with gusts between 20 and 30
mph, however stronger northwesterly winds are occuring just
offshore. Tonight temperatures will cool into the upper 40s to mid
50s across much of the region. However, increasing cloud cover from
an approaching cold front is likely which may limit radiational
cooling.

Rain showers return to the region on Monday, first over the North
Bay around or after sunrise and then over the greater San Francisco
Bay Area by midday. Isolated thunderstorms are also expected as the
front progresses southward into the Central Coast by early
afternoon. This is as CAPE values approach 500 J/kg and lapse rates
reach or exceed 7 C/km as the airmass aloft becomes more unstable
late Monday morning through the evening. The front is currently
expected to clear the Central Coast around 7 PM PDT with post-
frontal rain showers and isolated thunderstorms continuing into
Monday night and Tuesday morning.

&&

.LONG TERM...
Issued at 215 PM PDT Sun Oct 12 2025
(Monday night through next Saturday)

On Tuesday, lingering post-frontal rain showers and isolated
thunderstorms will persist, especially over the Central Coast before
the mid/upper level low pushes inland. Winds will be strongest over
the Central Coast and into the Diablo Range Monday afternoon and
into Tuesday morning with southwesterly gusts up to 50 mph,
especially in the higher elevations. This does not appear to be long-
lived  or encompass enough of an area to warrant a Wind Advisory,
however we will continue to monitor closely.

Rain chances will greatly diminish Tuesday night and moreso into
Wednesday as the pushes into Nevada. In fact, most of the day on
Wednesday will be dry across the region. Rainfall totals from Monday
through Tuesday night: 0.25"-0.75" across the North Bay; 0.50"-1.00"
across the Bay Area, East Bay, South Bay, and southern Salinas
Valley; 1.00"-1.25" around the Monterey Bay; 1.25"-1.75" in the
Santa Cruz Mountains, Santa Lucia Range, and Diablo Range. Isolated
higher amounts up to 3.00" will be possible especially in the higher
peaks of the Santa Cruz Mountains and Santa Lucia Range. Any heavier
showers and/or thunderstorms will be capable of producing lightning,
brief heavy downpours, and gusty, erratic winds. This amount of
rainfall would lead to minor/nuisance flooding concerns across much
of the Central Coast.

Tuesday night will be a cold one, with the coldest temperatures
expected across interior Central Coast with lows dropping into the
upper 30`s to lower 40`s. From the previous forecaster: "With the
recent rainfall, conditions will feel colder than what the
thermometer reads - please take care of people, pets, and plants.

Global ensemble clusters are in agreement that the upper-level low
will weaken and shift east Wednesday into Thursday with the help of
upper-level shortwave ridging nosing in from the Eastern Pacific
Ocean. This feature will quickly get flattened by an upper-level
shortwave trough, putting the region under the influence of the
eastern periphery of the high pressure over the Eastern Pacific
Ocean. This will translate to a warming and drying trend Wednesday
through Saturday."

&&

.AVIATION...
(06Z TAFS)
Issued at 922 PM PDT Sun Oct 12 2025

High clouds will lower through the night as a deep low pressure
system brings unsettled weather through the day Monday. Scattered
showers will arrive to the North Bay around 15-18Z and quickly spread
south through the afternoon. High resolution models are suggesting
an organized line of convection will push through the Bay Area
from 21Z-00Z. This line could bring strong showers or
thunderstorms to any of the terminals. By 00Z-03Z showers will
become more scattered, but will continue through the TAF period
outside of the North Bay, where drier air will begin to settle in.

Vicinity of SFO...Strong onshore winds will continue through the
night as the approaching low pressure system creates a gradient
that is overcoming the typical nocturnal lull in winds. Showers
could arrive as early as 15Z, but the stronger line with
thunderstorm chances looks to push through around 20-22Z. That`s
the time to watch for SFO. By 03Z the showers will become isolated
and weaker, but a second push is possible Tuesday afternoon
(outside of the TAF period).

SFO Bridge Approach...The approach will be impacted by ceilings
between 030 and 050 starting around 15Z.

Monterey Bay Terminals...Some sneaky stratus has formed at MRY and
SNS while my attention was focused on the incoming storm. It`s
hard to say if these clouds will make it through the night as the
atmosphere destabilizes, but it`s typically best not to bet
against the stratus. The front will arrive a couple hours later
for the Monterey Bay terminals, but they also have the best chance
for thunderstorms to form over the terminal. I`ve included VCTS
for both MRY and SNS as the main band goes through. It`s looking
more and more likely that thunderstorms will form, at least over
the water.

&&

.MARINE...
(Tonight through next Saturday)
Issued at 839 PM PDT Sun Oct 12 2025

Strong NW winds continue tonight as a deep low pressure system
moves in from the north. By late Monday morning, this system will
bring strong showers and possible thunderstorms. Any thunderstorms
that develop could bring localized gales, steep wind waves,
reduced visibility and a slight chance for waterspouts. The
showers will persist Tuesday, but become more isolated through the
day while the winds decrease. Rough seas to 10 feet will persist
into Wednesday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PDT Monday for SF Bay N of Bay
     Bridge.

     Small Craft Advisory until 3 AM PDT Monday for Mry Bay-Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 PM PDT Monday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt
     Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm.

     Small Craft Advisory from 3 PM to 9 PM PDT Monday for Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 PM PDT Monday for Pigeon Pt to Pt
     Pinos 10-60 NM.

&&

$$

SHORT TERM...RGass
LONG TERM....RGass
AVIATION...Flynn
MARINE...Flynn

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