715
FXUS66 KMTR 120938
AFDMTR

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

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

.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...
(06Z TAFS)
Issued at 955 PM PDT Sat Oct 11 2025

VFR throughout the region with breezy northwesterly flow steadily
diminishing overnight. Very low confidence (around 20% probability)
for fog impacts in the North Bay valleys, and have improved the
forecast visibility at STS as a result. Developing stratocumulus in
the Santa Lucia range results in a low confidence stratus impact for
MRY overnight. Any developing stratus and fog dissipates early
Sunday morning with breezy and gusty northwest winds resuming in the
afternoon. Towards and after the end of the 24-hour TAF period,
confidence in winds decreases with some models showing the winds
picking up as a strong low pressure system approaches the region.
For now, have kept winds below critical thresholds for the extended
TAFs at SFO and OAK, but will monitor further model guidance through
the next day.

Vicinity of SFO... High confidence of VFR through the TAF period.
Light northwest breezes overnight before stronger winds with gusts
to 25 kt resume Sunday afternoon. Some model data suggests that the
gusts will increase towards the end of the TAF period, but have kept
the gusts below 30-35 kt at this time. Increasing high clouds should
be expected Sunday night in advance of the low pressure system on
Monday.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... High confidence of VFR through the TAF
period at SNS. Developing stratocumulus in the northern Santa Lucia
range may impact MRY overnight, but this is a low confidence
forecast (around 10-20% probability) and the TAF remains VFR
throughout. Will monitor evolution of the clouds overnight. Light
winds overnight before breezy northwest flow resumes Sunday
afternoon. Lower confidence in wind speed and direction towards the
end of the TAF period. Have opted for a "worst-case" scenario in the
TAFs, for lack of a better term, but it is possible for winds at SNS
to be significantly weaker or for northwest winds at MRy to continue
through the end of the TAF period.

&&

.MARINE...
(Tonight through next Friday)
Issued at 955 PM PDT Sat Oct 11 2025

Strong to near gale northerly gusts continue across the waters,
resulting in hazardous conditions with locally stronger winds and
a Gale Warning along the Big Sur coastline. Occasional gale force
gusts are possible on Sunday across the northern waters, and the
windy pattern will persist into early next week. The pattern for
the first half week remains unsettled with more wind and rain
expected.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 3 AM PDT early this morning for Mry
     Bay.

     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 Arena to Pt
     Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to
     Pigeon Pt 0-10 nm.

     Gale Warning until 3 AM PDT early this morning for Pt Pinos to
     Pt Piedras Blancas 0-10 nm.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...DialH
MARINE...DialH

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