833
FXUS66 KMTR 121823
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1123 AM PDT Sun Oct 12 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 236 AM PDT Sun Oct 12 2025

 - Cold and windy conditions today

 - Widespread rainfall and a chance for thunderstorms Monday and
   Tuesday

 - Warming and drying trend kicks off Wednesday

&&

.SHORT TERM...
Issued at 236 AM PDT Sun Oct 12 2025
(Today and tonight)

It`s going to be a cold start to the morning. Conditions are cooler
and drier than they were 24 hours ago. This is thanks to light
offshore flow and subsequently clear skies that are allowing for
enhanced radiational cooling. Sensible weather today will remain
cool and windy with below normal temperatures and moderate
northwesterly breezes. Wind gusts will be locally stronger along the
coast, down northwest-southeast oriented valleys (namely the North
Bay Interior Valleys, Santa Clara Valley, and Salinas Valley), and
through gaps and passes with gusts up to 30 mph to be expected. If
you have not done so already, there is still time today to clean out
your gutters and secure/store any outdoor items that are sensitive
to rain and/or wind ahead of tomorrow`s system.

&&

.LONG TERM...
Issued at 236 AM PDT Sun Oct 12 2025
(Monday through Saturday)

A gale force low pressure system with support aloft in the form of a
reinforcing upper-level low will begin sliding down the West Coast
today - this will be the driver of our weather the next two days.
The Polar Jet Stream also dives south with this feature, but the
placement doesn`t seem to be too notable for our region in terms of
jet theory. The forecasted arrival time and heaviest rainfall period
has trended earlier as this is now looking like a Monday-Tuesday
event with the heaviest rainfall on Monday rather than a Monday-
Wednesday event with the heaviest rainfall on Tuesday. The brief
drying trend and offshore flow from this weekend has effectively
erased the marine layer with further drying expected through
tonight. As such, virga in the pre-frontal environment will work to
saturate the column early Monday morning ahead of the bulk of the
rainfall with the cold frontal passage Monday afternoon and evening.
The Weather Prediction Center has highlighted the region for a
marginal risk (at least 5%) of rainfall exceeding flash flood
guidance Monday morning through Tuesday morning. This means that
isolated flash floods are possible, but that they would be localized
and primarily affect places that can experience rapid runoff with
heavy rainfall. Post-frontal rain showers and thunderstorms will be
the name of the game on Tuesday. The thunderstorm potential on
Monday and Tuesday can be characterized by low CAPE (500 J/kg) and
conditionally unstable lapse rates (7 degrees Celsius/kilometer).
The Storm Prediction Center has highlighted the region for general
thunder during this time; remember, all thunderstorms are capable of
producing lightning and flooding, when thunder roars, go indoors!
and see a flash, dash inside! When all is said and done, a majority
of the area will accumulate 1.00" with locally higher totals of
1.50"-2.50" in the higher terrain of the East Bay, South Bay, and
Central Coast. This system is also going to be a cold one with 850
millibar temperatures putting daily minimum records in jeopardy.
Near-freezing temperatures are forecast for far interior portions of
Monterey and San Benito Counties Tuesday night. With the recent
rainfall, conditions will feel colder than what the thermometer
reads - please take care of people, pets, and plants. Patchy frost
is also possible during this time for the Interior East Bay and
Interior South Bay.

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...
(18Z TAFS)
Issued at 1123 AM PDT Sun Oct 12 2025

Gusty west to northwest winds are expected this afternoon before
winds shift southerly overnight ahead of the incoming low pressure
system. Rain chances increase early tomorrow morning with drizzle to
light rain possible 12Z through 15Z. The first round of showers
arrives around 15Z with moderate rain expected to continue into the
afternoon. Temporary fluctuations in visibility and ceiling height
are possible as showers move over TAF sites. For LVK, MRY, and SNS,
rain chances increase after the end of this TAF period (late Monday
morning into the early afternoon). Thunderstorm chances increase
after 18Z with a 20-25% chance of thunderstorms across the Bay Area
and a 20-30% chance across the Central Coast. Thunderstorms could
develop as early as 15Z for portions of the Bay Area but confidence
is lower as there is only a 10-15% chance at that time. Currently
did not include thunderstorms in the TAFs but this may be adjusted
in the next TAF issuance as confidence increases.

Vicinity of SFO...Gusty west to northwest winds expected with some
potential for gusts to around 30 knots Monday afternoon/evening.
Drizzle to light rain is possible at SFO as early as 12Z with higher
confidence in moderate rain/showers reaching SFO by 15Z. Rain will
then continue through the rest of the TAF period. There is a 20-25%
chance of thunderstorms impacting SFO after 18Z Monday as the low
pressure system enters the Central Coast. Currently do not have t-
storms in the TAF but they may be added in the next TAF issuance as
confidence continues to increase. The most likely timeframe for t-
storm development at SFO will be 18Z Monday to 03Z Tuesday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Moderate west to northwest winds continue
through the TAF period. Winds gradually shift southerly Monday
morning as low pressure system moves inland. Rain chances increase
as early as 15Z when showers approach the Monterey Peninsula. Higher
confidence in more moderate rain reaching MRY and SNS Monday
afternoon/evening with a 20-30% chance of thunderstorms.
Thunderstorms are most likely just after the end of this TAF period
(21Z Monday to 06Z Tuesday).

&&

.MARINE...
(Today through Friday)
Issued at 1123 AM PDT Sun Oct 12 2025

Hazardous conditions continue across the waters through Monday
afternoon with rough seas and significant wave heights up to 12
feet  expected. Gusty, strong to near gale, northerly winds
continue to  strengthen over the outer waters as a developing
storm system  approaches coastal California. Gale force to near
gale force gusts  will develop across the far northern outer
waters and along the Big  Sur coast Sunday afternoon. Rain showers
with embedded thunderstorms  are expected Monday through late
Tuesday over the coastal waters as  a low pressure system moves
into the Central Coast. Mariners can  expect to experience locally
rough seas, gusty winds, and steep  waves if they encounter a
thunderstorm.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 9 PM this evening to 5 AM PDT Monday
     for SF Bay N of Bay Bridge.

     Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this
     evening for Mry Bay.

     Small Craft Advisory until 3 PM PDT this afternoon for Pt Arena
     to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos
     to Pt Piedras Blancas 0-10 nm.

     Gale Warning from 3 PM this afternoon to 9 PM PDT this evening
     for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60
     NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory until 9 AM PDT Monday for Pigeon Pt to Pt
     Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Reyes to
     Pigeon Pt 0-10 nm.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Kennedy
MARINE...Kennedy

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