FXUS66 KMTR 230612
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1012 PM PST Mon Dec 22 2025
...New AVIATION, 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.
&&
.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...
(06Z TAFS)
Issued at 1012 PM PST Mon Dec 22 2025
Rain has shifted north into the Mendocino County / the northwest
portion of California this evening. Mainly dry conditions should
prevail overnight, with perhaps a few showers skirting by in the
North Bay. CIGs vary from IFR to MVFR now rather than fog
developing, this should hold overnight. There may be some periods
Tuesday afternoon where cigs lift a category, but they'll falter
once the rain arrives. Winds gradually pick up late Tuesday morning
and into the afternoon, before ramping up Tuesday night into
Wednesday.
Vicinity of SFO...Satellite shows some a mix of cumulus and cirrus
around the Bay Area, leaving us with CIGS bouncing between MVFR and
VFR. Shower chances should be little to none overnight,
reflecting the RRFS based on current radar trends. Confidence is
medium on precip timing overnight and into tomorrow. Looking at
Tuesday afternoon and beyond, we're watching the wind threat. A
storm system will bring rapidly increasing winds from the south
late Tuesday afternoon and into the evening. Expect winds to peak
late in the day and overnight with gusts exceeding 40 knots. 40kt
gusts have been added at 6Z, these may need to be raised higher.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...CIGS filled in this evening around the Bay,
with conditions bouncing between IFR and VFR. Confidence is medium
on the overnight cloud deck as most models flirt with MVFR CIGs
around MRY and SNS. Tomorrow southerly winds begin to increase in
the afternoon.
&&
.MARINE...
(Tonight through next Sunday)
Issued at 1012 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 10 AM PST Tuesday through Friday evening for
CAZ006-508>510-512>518-528>530.
Wind Advisory from 4 PM Tuesday to 4 AM PST Wednesday for CAZ006-
504-506-508-510-512>516-518-528-529.
Flood Watch through Friday evening for CAZ502>506.
High Wind Warning from 4 PM Tuesday to 4 AM PST Wednesday for
CAZ502-503-505-509-517-530.
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...KR
MARINE...BFG/KR
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Prepared by Boulder-Creek.com Weather at: Mon Dec 22 22:30:02 PST 2025
From the National Weather Service
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