FXUS66 KMTR 230008
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
408 PM PST Mon Dec 22 2025
...New SHORT TERM, LONG TERM, MARINE...
.KEY MESSAGES...
Updated at 407 PM PST Mon Dec 22 2025
- Flood Watch remains in effect for the North Bay through Friday evening;
Flood Watch for the rest of Bay Area and Central Coast begins
Tuesday morning at 10 AM PST
- Light to moderate rain at times continues this evening with
minor nuisance flooding and rises in rivers/streams across
North Bay possible. Turn Around, Don't Drown!
- Increasing chances for urban flooding and extensive travel
delays late Tuesday into early Friday across entire Bay Area
and Central Coast as widespread heavy rain returns
- Very hazardous, impactful winds Tuesday through early Friday along
our entire coastline and higher elevations inland with power
outages likely
- A slight chance of severe thunderstorms with strong wind gusts
late Tuesday through Thursday
- Dangerous beach conditions anticipated late Tuesday through
Friday for all Pacific Coast Beaches&&
.SHORT TERM...
Issued at 407 PM PST Mon Dec 22 2025
(This evening through Wednesday)
We're in a welcomed lull of moderate to heavy rainfall through late
Tuesday afternoon for inland low lying areas. However, our coastal
ranges, especially in the North Bay may see between 0.50"-1.00" of
rain through tomorrow afternoon.
Meanwhile, overnight, a rapidly intensifying area of low pressure
well offshore, will begin its trek northeast taking aim at NorCal
and the Bay Area. The powerful synoptic storm system will bring its
own source of moisture while combining with the remaining moisture
from the shifting atmospheric river to the south. The closed low
associated with the powerful offshore troughing won't be off the
coast of Washington until late tom tomorrow night, a testament to the
potent strength in the sharpening trough to our west. The winds over
our coastal waters will begin to ramp up Tuesday morning. By Tuesday
afternoon and evening along our coast there is approximately a 80%-
90% chance of wind gusts exceeding 40 MPH, and 50%-70% chance
farther inland, especially at higher elevations. Bottom line, it's
going to start to get windy across our entire area the second half
of tomorrow. The first wave of moderate to heavy rainfall will reach
the North Bay soon after sunset tomorrow, with up to an inch of rain
along our coastal ranges and the North Bay by midnight.
&&
.LONG TERM...
Issued at 407 PM PST Mon Dec 22 2025
(Wednesday night through next Monday)
Tuesday night into Wednesday morning will see the first of several
waves of strong winds and heavy rainfall move onshore. As mentioned
above, the North Bay will feel the leading edge of the first wave of
strong showers, scattered thunderstorms and moderate to heavy
rainfall at times, but the impacts will quickly spread south and
inland across our entire area by sunrise Wednesday morning. While
the first strong low pressure moves onshore early Wednesday morning,
a second more powerful area of low pressure will quickly approach on
the heels of the first. As the upper trough offshore sharpens and
continues to deepen, it will also take on a negative tilt by
Wednesday evening. The strengthening surface low and wide swath of
divergent, 90kt-100kt 500mb flow, will produce an environment
favorable for low top supercells and the potential for waterspouts.
There is a small but non-zero chance for any water spouts that do
develop to move onshore as short lived tornadoes or produce strong
straight line winds, first along the Central Coast from late
Wednesday afternoon through late Wednesday night, then farther north
into the Bay Area and North Bay during the overnight into early
Thursday (Christmas) morning.
That part of the forecast will jump off the page, but the primary
concerns continue to be the widespread moderate to heavy rainfall
leading to urban flooding, land/rock slides, downed trees and
overall hazardous driving conditions during two of the busiest
travel days of the year. Give yourself plenty of time to reach your
destination and slow down, keeping plenty of distance between you
and other vehicles. Along with the extensive travel delays, there is
potential for widespread power outages as the numerous (at least 3-
4) lines of showers, thunderstorms and strong winds move onshore
over a 60hr period from late tomorrow night through early Friday
morning.
The urban and nuisance flooding potential in poor drainage areas
will be widespread across our whole area late Tuesday through early
Friday. Flooding of rivers, streams and creeks will mostly remain in
the North Bay, which has seen the most rainfall over the past few
days of the atmospheric river out ahead of the more progressive
waves ejecting inland from the powerful offshore trough. The Russian
River in Geyserville is forecast to approach action stage early
Wednesday morning after sunrise. The Mark West Creek near Mirabel
Heights is currently in action stage, will recede gradually during
the day tomorrow, but forecasted to reach minor flooding stage by
early Christmas morning, peak Friday morning below moderate Friday
morning and then begin to recede through the weekend.
&&
.AVIATION...
(18Z TAFS)
Issued at 1128 AM PST Mon Dec 22 2025
Frontal boundary is hanging over the area this morning bifurcating
the Bay Area at the Golden Gate. This boundary will slowly lift to
the north through the day. This will allow for some clearing with
scattered showers south of the boundary while widespread rain
will ride the boundary north. Winds south of the boundary will
generally be out of the south while north of the boundary will
generally be out of the north. Eventually the boundary will lift
out of the Bay Area allowing for scattered showers across the
region. By late Tuesday morning, expect strong gusty winds from
the south to develop, accompanied by widely scattered showers.
Vicinity of SFO...Showers will be the main story at SFO today.
Winds will remain out of the south, but on the lighter side of the
coin. CIGS will bounce a bit with showers in the area, but
generally should remain VFR or MVFR. The only concern I have over
the next 24 hours would be light winds overnight, wet grounds, and
radiational cooling, leading to some localized fog development.
This remains a spot of contemplation, but needs to be noted. The
big story is on Tuesday as a potent system approaches from the
southwest and brings rapidly increasing winds from the south.
Expect winds to peak late in the day and overnight with gusts
exceeding 40 knots.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Light to moderate winds out of the SE
with an occasional passing shower. Winds ramp up Tuesday
afternoon.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 407 PM PST Mon Dec 22 2025
Life threatening conditions will develop across all water on
Tuesday into Tuesday night. Storm conditions will dominate the
open Pacific waters while Gale conditions plague the bays. Steep
open ocean waves will be to near 20 feet under these winds. While
a lull in winds will occur during the day Wednesday, strong gales
are expected again Wednesday night into Thursday morning.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from Tuesday morning through Friday evening for
CAZ006-508>510-512>518-528>530.
High Wind Watch from Tuesday evening through late Tuesday night
for CAZ006-502>506-508>510-512>518-528>530.
Flood Watch through Friday evening for CAZ502>506.
PZ...Gale Warning from 9 AM Tuesday to 3 AM PST Wednesday for Mry Bay-
SF Bay N of Bay Bridge.
Storm Warning from 9 AM Tuesday to 3 AM PST Wednesday 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
Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-
10 nm.
&&
$$
SHORT TERM...JM
LONG TERM....JM
AVIATION...BFG
MARINE...BFG
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Prepared by Boulder-Creek.com Weather at: Mon Dec 22 16:30:02 PST 2025
From the National Weather Service
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