316
FXUS66 KMTR 130908
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
208 AM PDT Mon Oct 13 2025

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

.KEY MESSAGES...
Updated at 205 AM PDT Mon Oct 13 2025

 - Widespread rainfall and thunderstorm chances today

 - Post-frontal rain showers and thunderstorms tomorrow

 - Warming and drying trend Wednesday through Saturday, unsettled
   weather returns Sunday

&&

.SHORT TERM...
Issued at 205 AM PDT Mon Oct 13 2025
(Today and Tuesday)

A developing gale force low pressure system off the
Oregon/Washington border will quickly dive down the West Coast today
with the help of a dip in the Polar Jet Stream. Rain showers are
underway north of our area with lightning remaining confined to
Oregon for the time being. During the beginning of this event, rain
showers are going to have a hard time making it to the surface. The
00Z October 13th KOAK sounding observed a precipitable water value
of 0.45 inches with a stout dry slot in the 900-750mb layer. The
latest aircraft sounding out of SJC observed a 0.593 inch
precipitable water value - this is likely due to mid-to-high level
clouds that have begun to stream into the region. Nonetheless, it`ll
likely be a virga show early this morning with perhaps an extra
beautiful sunrise. The morning commute should not be impacted by
rain or thunderstorms - the same cannot be said for the evening
commute. Clouds will lower through the morning with rainfall
increasing in coverage and intensity through the afternoon and into
the evening. Ahead of the cold front, strong southwesterly winds can
be expected with gusts up to 35 mph in the higher terrain of the Bay
Area and gusts of 35-45 mph in the higher terrain of the Central
Coast. Rainfall totals will be highly dependent upon where rain
showers/thunderstorms develop. Speaking of thunderstorms, the
critical ingredients of lift, instability, and moisture will all be
present. The low CAPE (500 Joules/kilogram with conditionally
unstable lapse rates of 7 degrees Celsius/kilometer) environment
will be capable of producing thunderstorms that will pose the
threats of lightning, nuisance flooding (particularly in urban areas
which are considered hydrophobic), small hail, erratic/gusty winds,
and waterspouts. Most of the rainfall expected with this system and
the best thunderstorm chances will be today. The Weather Prediction
Center has highlighted our area for a marginal risk (at least 5%) of
rainfall exceeding flash flood guidance which 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. As the surface low pressure system and it`s accompanying
cold front eject to the southeast late tonight, post-frontal rain
showers and thunderstorms will remain possible Tuesday. This system
is also going to be a cold one with the 850 millibar temperature
daily minimum record in jeopardy on Tuesday. At the surface, SJC is
forecast to jeopardize their daily low maximum temperature - the
official forecast is 63 degrees Fahrenheit with the record of 62
degrees Fahrenheit dating back to 1948, the period of record is
1893. Cold, clear, and calm conditions Tuesday night will yield two
hazards: near-freezing temperatures for far interior Monterey and
San Benito Counties east of Highway 101 and widespread fog. With
rainfall preceding this, conditions can be expected to feel colder
than what the thermometer reads - please take care of people, pets,
and plants. Additionally, patchy frost and black ice will be
possible within sheltered interior areas as well. Outside of these
areas, it will still be cold, so it may not be a bad idea to pull
the winter linens out.

&&

.LONG TERM...
Issued at 205 AM PDT Mon Oct 13 2025
(Wednesday through Sunday)

The upper-level low will slowly get nudged east by upper-level
shortwave ridging nosing in from the Eastern Pacific Ocean, this
will result in a brief warming and drying trend Wednesday through
Saturday. ECMWF and GFS are in agreement that longwave upper-level
troughing and rain will return Sunday. There`s a significant amount
of spread between their ensembles, but it is still worth mentioning.

&&

.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 this morning for SF Bay N of
     Bay Bridge.

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

     Small Craft Advisory until 3 PM PDT this afternoon 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 this afternoon to 9 PM PDT this
     evening for Pt Pinos to Pt Piedras Blancas 0-10 nm.

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

&&

$$

SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Flynn
MARINE...Flynn

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea