648
FXUS66 KMTR 111100
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
400 AM PDT Sat Oct 11 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 305 AM PDT Sat Oct 11 2025

 - Cool and windy conditions through the weekend

 - Widespread rainfall Monday through Wednesday with a chance for
   thunderstorms Monday and Tuesday

&&

.SHORT TERM...
Issued at 305 AM PDT Sat Oct 11 2025
(Today and tomorrow)

The positively tilted longwave trough will be the driver of our
weather over the weekend. Sensible weather will be cold and windy,
especially today as the trough axis moves through. Winds will likely
be more impactful than the relatively cold temperatures. The
orientation of the aforementioned feature will favor
northwest/southeast oriented valleys, namely the North Bay Interior
Valleys, Santa Clara Valley, and Salinas Valley, as well as the
coastline, gaps, passes, and higher terrain which can expect gusts
up to 40 mph. Preparations for the upcoming system such as cleaning
out gutters, securing loose outdoor items, and properly storing
outdoor items that are sensitive to rain and/or wind should be
finalized this weekend.

&&

.LONG TERM...
Issued at 305 AM PDT Sat Oct 11 2025
(Monday through Friday)

A gale force low pressure system with support aloft in the form of a
reinforcing upper-level low near the Washington/Canada border will
slink down the West Coast beginning Monday. This system will bring
an influx of moisture with precipitable water values exceeding one
inch and IVT values of 250 kg/ms. Between Monday and Wednesday, this
system is forecast to bring widespread rainfall totals of one inch
with locally higher totals of two to three inches in the higher
terrain. As this low is forecast to be off the San Francisco
Peninsula Coast, cyclonic rotation will result in southwesterly flow
into the Central Coast. As a result, the Santa Cruz Mountains and
Big Sur Coast are forecast to receive the most rainfall. The Weather
Prediction Center has highlighted the region for a marginal risk (at
least 5%) of rainfall exceeding flash flood guidance Monday morning
through Wednesday morning. This means isolated flash floods are
possible, but would be localized and primarily affecting places that
can experience rapid runoff with heavy rainfall. Monday and Tuesday
will bring the threat for thunderstorms across the area as the
critical ingredients of lift, instability, and moisture will all be
present. Lift and moisture have already been discussed, so it`s time
to talk about instability. Cold air aloft will destabilize the
atmosphere, yielding conditionally unstable lapse rates of 7 degrees
Celsius/kilometer and low CAPE of 400 Joules/kilogram. The Storm
Prediction Center has highlighted the region for general thunder on
Monday morning through Tuesday morning, this will likely get
extended into Wednesday morning in the next 24 hours or so.
Remember: lightning/flooding threats exist with all thunderstorms,
when thunder roars, go indoors! and see a flash, dash inside! Wind
will be another concern during the Monday and Tuesday timeframe.
There`s up to a 50% chance that locations along the San Francisco
Peninsula Coast, down the Santa Clara and Salinas Valleys, and
through the Altamont Pass reach gusts of 45 mph. As of now, this
does not appear to be long-lived or encompass enough of an area to
warrant a Wind Advisory. Still, loose outdoor items should be
secured ahead of time (ideally this weekend). When it comes to the
rain and wind, extra caution should be exercised when driving next
week. Beyond Wednesday, there is uncertainty in the progression of
the upper-level pattern, but it does look like shortwave ridging
will build, resulting in at least a brief warming and drying
trend.

&&

.AVIATION...
(12Z TAFS)
Issued at 356 AM PDT Sat Oct 11 2025

Low stratus and fog have developed in the North Bay overnight
with IFR vis and ceilings at KSTS and KAPC. Most recent trends
have shown some improvement wrt to vis but otherwise, fog is
expected to clear out by mid-morning with VFR expected for the
remainder of the TAF period. However, there is a chance of fog
developing once again early Sunday morning.

Vicinity of SFO...Some low stratus lingers in vicinity of the Bay
Area terminals overnight, but VFR is expected to prevail through the
forecast period with breezy onshore winds developing this afternoon
and persisting until later tonight.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Similar to the Bay Area terminals, some low
stratus lingers in vicinity of the terminals with VFR expected to
prevail through the forecast with some borderline MVFR ceilings
possible this morning. Breezy onshore flow will develop this
afternoon and persist through the evening hours.

&&

.MARINE...
(Today through Thursday)
Issued at 305 AM PDT Sat Oct 11 2025

Northerly winds will steadily increase this morning across our
southern waters, with moderate northerly winds eventually
spreading north across our outer and coastal waters. A Gale
Warning is in place from Pigeon Point south through Monterey Bay
and the Big Sur coastline this afternoon through early Sunday
morning. Along the with the moderate to strong winds expect rough
seas to build through Sunday. The pattern for the first half week
remains unsettled with more wind and rain expected.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory until 10 AM PDT this morning for CAZ506.

PZ...Gale Warning from 3 PM this afternoon to 3 AM PDT Sunday for Mry
     Bay-Pt Pinos to Pt Piedras Blancas 0-10 nm.

     Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Sunday
     for Pt Arena to Pt Reyes 0-10 nm-Pt Reyes to Pigeon Pt 0-10
     nm.

     Gale Warning from 3 PM this afternoon to 4 PM PDT Sunday for
     Pigeon Pt to Pt Pinos 0-10 nm.

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

     Small Craft Advisory from 3 PM this afternoon to 4 AM PDT Monday
     for Pt Arena to Pt Reyes 10-60 NM.

     Small Craft Advisory from 9 AM this morning to 4 AM PDT Monday
     for Pigeon Pt to Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...JM
MARINE...JM

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