FXUS66 KMTR 180521
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
921 PM PST Wed Dec 17 2025
...New UPDATE, AVIATION, MARINE...
.KEY MESSAGES...
Updated at 304 AM PST Wed Dec 17 2025
- Mostly dry for tonight and Thursday with the exception of
coastal drizzle tonight into early Thursday morning.
- Patchy to Areas of dense fog likely overnight
- Rain, wind, and general thunderstorms Sunday
- Rainy and windy conditions are expected to continue through the
holiday into the end of next week
&&
.UPDATE...
Issued at 921 PM PST Wed Dec 17 2025
Radiative stratus and fog is developing across the inland valleys
and the Monterey Bay region tonight, expected to continue to expand
across the Bay Area as the night progresses. Dense Fog Advisories
have been issued for the East Bay Interior Valleys, the Northern
Monterey Bay region (namely, the coastal plain of Santa Cruz
County), and the Monterey Bay itself through 7 AM Thursday. Will
continue to monitor the development of stratus and fog overnight in
case additional advisories are necessary. If you encounter dense fog
while driving, slow down, use low beam headlights, and leave extra
space between you and the car in front of you.
DialH
&&
.SHORT TERM...
Issued at 226 PM PST Wed Dec 17 2025
(This evening through Thursday)
A mix of sun and clouds for the remainder of the afternoon in the
wake of a relatively weak cold front that pushed through our area
earlier this morning. Rainfall received overnight and this morning
was beneficial with most low lying areas seeing around a tenth-of-an-
inch, and higher elevations seeing from a tenth-of-an-inch to half-
an-inch. Expect areas of dense fog to develop overnight within
inland valleys. especially the North Bay, Bay Area and East Bay.
Closer to the coast, fog and drizzle will combine to limit
visibility overnight into early Thursday morning.
Thursday will be mostly dry with the exception of the coastal
drizzle that should taper off an hour or two after sunrise.
Thursdays high temperatures will be right around normal, slightly
above normal for higher elevations within the Central Coast. The
first wave of numerous rounds of rainfall will first move into the
North Bay late in the day Thursday with only light rain for the
onset into Friday.
&&
.LONG TERM...
Issued at 226 PM PST Wed Dec 17 2025
(Thursday night through next Tuesday)
Plenty of uncertainty remains with the exact timing and intensity of
the rainfall we're expecting to impact our area beginning Friday
through the remainder of the extended forecast. What we do know attm
is the North Bay will see the most rainfall as several waves of
moderate/heavy rainfall push through over the next week, along with
elevated coastal ranges from San Mateo south through the Santa Cruz
mountains into the Santa Lucia's. The period of heaviest rainfall as
of this writing looks to be late Saturday night through early Monday
morning, which means Sunday may be difficult travel day. Give
yourself plenty of extra time to travel at anytime over the next
week, but especially Sunday.
The totals over the coastal ranges will standout on ours and others
weather maps you'll see as we head into one of the busiest travel
times of the year. However, low lying areas all across our region
will see plenty of impacts from the rain, wind and other cumulative
problems associated with multiple storm systems moving over our
area. By the beginning of next week we are likely to see rivers
begin to swell and the potential for rock and land slides to
interfere with travel plans. Signals for rainfall chances beyond the
scope of our official forecast persist into the end of next week as
well.
Most of the Pacific Coast is highlighted in CPC outlooks for
excessive rainfall through the extended forecast. Please monitor
our web page (weather.gov/mtr) for updated rainfall total maps,
more specific timing and impacts for our area along with our
partners at the CPC for bigger picture products across the West
Coast (cpc.ncep.noaa.gov).
&&
.AVIATION...
(06Z TAFS)
Issued at 921 PM PST Wed Dec 17 2025
Generally radiative stratus and fog is developing across the
interior valleys and Monterey Bay region, with a patchwork of MVFR-
LIFR conditions across the impacted region. General expectation is
for the stratus deck to expand through the night with conditions
gradually improving through Thursday morning. Around that time, a
band of MVFR clouds will come into the North Bay associated with an
incoming frontal system, with STS not clearing out to VFR and APC's
clearing a moderate confidence forecast. The rest of the region
should get VFR conditions with light onshore flow Thursday afternoon
with stratus returning late in the evening hours. Rain chances begin
Thursday evening, favoring the North Bay and windward slopes across
the Bay Area, expanding in coverage after the end of the 24-hour TAF
period.
Vicinity of SFO... VFR conditions continue through the next several
hours with light winds. Moderate confidence that MVFR stratus
returns to the terminal around midnight with a gradual diminishing
to IFR conditions through the pre-dawn hours. The latest high
resolution model output depicts the stratus developing mainly over
the SF Bay and the eastern shore, but retains enough of a signal for
impacts to the terminal to keep the previous forecast in place.
Clearing is expected late Thursday morning, with a return to breezy
west-northwest winds in the afternoon. Stratus returns late Thursday
evening in advance of a rain band expected to arrive close to the
end of the TAF period.
SFO Bridge Approach... Somewhat higher confidence in direct stratus
impacts to the approach path tonight. Otherwise similar to SFO.
Monterey Bay Terminals... LIFR stratus through the night with
shallow fog possible at the terminals. VFR conditions return late
Thursday morning with the return of breezy northeast winds. MVFR
stratus returns to MRY near the end of the TAF period, and to SNS
shortly afterwards, as the frontal band approaches the region.
&&
.MARINE...
(Tonight through next Tuesday)
Issued at 921 PM PST Wed Dec 17 2025
Dense fog continues across parts of Monterey Bay and is expected
to persist through the early morning hours. Low visibilities will
create hazardous conditions for mariners, who should proceed with
caution, use proper fog signals, and make sure all running lights
are on. Light to moderate onshore breezes prevail with moderate
seas through late week. Rain chances return to the northern waters
on Thursday night and push southward through the day on Friday.
Additional rain arrives Saturday night and continues off and on
at times through much of next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory until 7 AM PST Thursday for CAZ510-529.
PZ...Dense Fog Advisory until 7 AM PST Thursday for Mry Bay.
&&
$$
SHORT TERM...JM
LONG TERM....JM
AVIATION...DialH
MARINE...DialH
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
Prepared by Boulder-Creek.com Weather at: Thu Dec 18 00:30:02 PST 2025
From the National Weather Service
|