100
FXUS66 KMTR 082343
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
443 PM PDT Wed Oct 8 2025

...New AVIATION...

.KEY MESSAGES...
Updated at 115 PM PDT Wed Oct 8 2025

 - Cooler and cloudier weather begins today, drizzle tonight and
   Thursday morning

 - Light rain chances increase Friday through Saturday morning for
   the North Bay

 - More significant rainfall possible early next week

&&

.SHORT TERM...
Issued at 115 PM PDT Wed Oct 8 2025
(This evening through Thursday)

Satellite imagery shows extensive stratus coverage across the North
Bay, barring interior Napa County, parts of the East Bay from
Concord and Mount Diablo west to the Bay, extending as far south as
Hayward, the city of San Francisco, western San Mateo County, Santa
Cruz County, and most of the southern Monterey Bay region. The
clouds will retreat towards the coast through the day, but most of
Sonoma and Marin Counties, in addition to western San Mateo County
and Santa Cruz County, are expected to remain socked in through the
rest of the day.

A pattern change today is causing cooler temperatures across the
region, as an upper level low off the Central Coast that contributed
to mild offshore flow yesterday was absorbed into a developing upper
level trough off the Pacific Northwest. A precipitous drop in
temperatures has been observed throughout all but the immediate
coastal region, with the RTMA analysis showing Bayside areas seeing
drops of 5 to 10 degrees from this time yesterday, while the inland
valleys seeing temperatures drop 15 degrees or more over the same
period. High temperatures top out in the middle to upper 70s for the
inland valleys, the lower to middle 70s for the Bayside areas, and
the middle to upper 60s for the Pacific coast. Tonight into Thursday
morning, a slight chance for drizzle arrives in the region with the
arrival of a weak surface low, which at the time of writing is
around 250 miles west of Point Conception, expected to continue
traveling towards the east. Any accumulating rainfall will be very
light, around a few hundredths of an inch at most. Otherwise,
Thursday`s conditions will be very similar to today`s.

&&

.LONG TERM...
Issued at 115 PM PDT Wed Oct 8 2025
(Thursday night through next Tuesday)

Temperatures remain remarkably stable into the upcoming weekend as a
couple of upper level trough axes marches through the West Coast.
Chances for light rain accompany one such trough axis on Friday
through Saturday morning, with rainfall totals once again remaining
light and non-impactful. The latest forecast shows wetting rains
(totals above 0.1") confined to the Sonoma Coastal range and the
Mayacamas, with a few hundredths of an inch in the Sonoma County
valleys and totals for the rest of the Bay Area and Central Coast at
0.01" at most.

As that trough axis moves onshore into the Pacific Northwest,
another axis develops from the same trough and reinforces the cooler
conditions through the weekend into the next week. That`s about as
much as can be confidently said about next week`s forecast. Ensemble
model clusters continue to depict a forecast where the impact levels
remain heavily sensitive to how the upper level pattern evolves.
Taking Day 6 (next Tuesday) as an example, potential scenarios
involve a stronger upper level low off the Pacific Northwest or
northern California, or a weaker low off Central California, perhaps
even an open trough over the West Coast. The scenarios that involve
the stronger low pressure systems are generally the ones that bring
more rain to the region than the ones with weaker lows or open
troughs. To give some numbers here: For the period from Monday the
13th at 5 AM, to Thursday the 16th at 5 AM, the National Blend of
Models gives an 80 percent chance that the rainfall total in
downtown San Francisco falls between 0 inches and 2.5 inches, while
there`s an 50 percent chance that the downtown San Francisco
rainfall total falls between 0.02 inches and 1.9 inches. Spare a
thought for our colleagues at Sacramento, Hanford, and Reno, who
have to deal with similar levels of uncertainty on top of the
possibility for significant snowfall in the Sierra Nevada. Needless
to say, the forecast will evolve and get refined over the next few
days.

&&

.AVIATION...
(00Z TAFS)
Issued at 433 PM PDT Wed Oct 8 2025

Mixed conditions today as a southerly surge brought in deep
moisture and a difficult forecast. Drier air now moving across the
Bay Area is expected to last into the evening before clouds
increase once again by around midnight local. Deep upper trough
swinging through the West Coast will provide a solid chance (near
certain) of DZ from KHAF northward, and a lesser chance for
points south into Thursday morning.

Vicinity of SFO...VFR through this evening before the
aforementioned dense cloudiness builds in by midnight, with DZ
lasting into the mid-morning Thursday. Several hints at southerly
winds at the terminal through the late morning hours, so moderate
confidence in impacts there. Beyond the morning, onshore flow
kicks in during the afternoon hours and VFR through the rest of
the period.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Lingering southerly component of the
winds will help keep stratus at bay, literally speaking, through
tonight. Slight chance of cloud cover increasing as temps cool
around sunrise, but moderate confidence in remaining VFR.
Otherwise, high confidence VFR forecast through the rest of
Thursday.

&&

.MARINE...
(Today through Monday)
Issued at 855 AM PDT Wed Oct 8 2025

Gentle to moderate SW winds will gradually shift back to a NW
breeze Thursday. Winds will increase to a strong NW breeze late
Saturday, building rough seas by Sunday. Disturbed conditions
with periods of rain and gusty winds are expected early next week.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Behringer
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