FXUS66 KMTR 231243
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
443 AM PST Tue Dec 23 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 210 AM PST Tue Dec 23 2025
- Flood watch continues for the North Bay through Friday evening;
Flood Watch for the rest of the Bay Area and Central Coast
begins at 10 AM PST this morning
- Light rain continues through this afternoon with moderate to
heavy rain returning Tuesday night into Wednesday morning.
Minor nuisance flooding remains possible today
- 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 with the potential to continue
into Friday
- Dangerous beach and marine conditions anticipated late Tuesday
through Friday for all Pacific Coast Beaches
&&
.SHORT TERM...
Issued at 210 AM PST Tue Dec 23 2025
(Today and tonight)
Scattered showers continue across the Bay Area as the main rainband
from Monday continues to drift northward. Light rain is expected to
continue primarily across the North Bay today with scattered showers
across the rest of the Bay Area and Central Coast. Offshore, an area
of low pressure currently located to our southeast will strengthen
as it moves northwards. The rapid deepening of this low pressure
system will create a very tight pressure gradient along our
coastline and result in very strong winds. Models continue to
highlight a 70-80 knot (80-90 mph) low level jet at 925 mb and a 500
mb jet max around 100 knots (115 mph) moving in over the Bay Area.
Some higher resolution models suggest that isolated hurricane force
gusts (74 mph+) could be possible offshore. The low pressure system
is set to move northwards parallel to our coastline with impacts
starting late Tuesday afternoon and continuing through early
Wednesday morning. In terms of wind impacts, confidence is highest
that gusts to around 65 mph will be limited to the coastline with
the potential for gusts to around 75 mph on isolated portions of the
coast. Gusts between 25 to 35 mph with gusts to 55 mph are expected
across the interior Bay Area late Tuesday into Wednesday.
Precipitation amounts for Tuesday have decreased with recent model
runs showing a messier, scattered system moving through the Bay Area
compared to the widespread, more stratiform like rain moving to our
north and south. Moderate to heavy rain is still expected late
tonight into Wednesday as the front moves through but heavy rain may
be more isolated in occurrence that originally forecast. The WPC
maintains a slight (15%) chance of excessive rainfall along the
coastline and a marginal (5%) for interior portions of the Bay Area
and Central Coast for Tuesday into early Wednesday. The more
scattered nature of precipitation will help to reduce more
widespread flooding impacts and keep them more localized to where
the heaviest rainfall is able to set up. The highest rainfall totals
are forecast to be within the coastal mountains of the North Bay,
Santa Cruz, and Santa Lucia Range.
There is also a 10-15% chance of thunderstorms with this system late
tonight into early Wednesday morning. In terms of favorability,
there is decent instability (MUCAPE values around 200-300 J/kg),
lift from the cold front, good amounts of moisture (PWAT values
around 1"), and strong low level wind shear. Wind shear is the most
favorable factor for thunderstorm development with guidance showing
surface to 1KM shear ranging anywhere from 30 knots to 45 knots.
Currently the SPC has a general mention of thunderstorms along the
California coast but, given the large amounts of low level shear,
there is the potential for severe thunderstorms to develop. If a
severe thunderstorm is able to develop it may produce a waterspout
or a weak tornado. The risk of this would be highest along the
coastline with SPC showing an increasing threat of severe weather
starting Wednesday.
While widespread flooding concerns appear lower with tonight's
system, it may still result in ponding on the roadway and sharp
rises in smaller streams and creeks (Mark West Creek, San Lorenzo,
etc). If you encounter flooding on the roadway, do not drive through
it - Turn Around, Don't Drown. With the combination of strong winds
and moderate to heavy rain, downed trees and power outages will
occur - especially if you live along the coast. Have multiple ways
to receive warnings in the event that flooding or severe weather
does occur.
&&
.LONG TERM...
Issued at 210 AM PST Tue Dec 23 2025
(Wednesday through Monday)
Impacts from the initial Tuesday night to Wednesday morning system
will decrease by late morning, but, a second potentially more
impactful system will arrive late Wednesday and continue through
Friday. This second system will follow a similar path as the first
with rapid deepening expected as it moves northwards, parallel to
the California coastline. This will bring another round of strong,
impactful winds with it but wind gusts will be slightly weaker than
they were compared to the first system. Multiple rounds of moderate
to heavy rain will move through the Bay Area and the Central Coast
with this system. The WPC has issued a slight risk of excessive
rainfall for much of our area Wednesday and a marginal risk of
excessive rainfall for the Big Sur coastline on Thursday. Given the
more widespread moderate to heavy rain for this system, flooding
will be more likely across urban areas with rises in smaller
streams/creeks and mainstream rivers likely (especially the Russian
River and Napa River). With the return of moderate to heavy rain and
strong winds, additional power outages and downing of trees is
expected Wednesday night into Thursday.
The biggest threat late Wednesday through Friday will be the
potential for severe weather, including the risk of weak tornadoes
and waterspouts. The SPC has issued a marginal risk of severe
thunderstorms and a 2% chance of tornadoes/waterspouts along our
entire coastline. The highest risk for a weak tornado/waterspouts
will be from embedded thunderstorms within the main rain band as the
cold front passes through our CWA. That being said, guidance shows
the potential for isolated cells to develop in the wake of cold
frontal passage which also display potential for severe thunderstorm
development and rotation. This system looks even more favorable than
the first system with much more instability (higher MUCAPE values
over a much larger area) and continued strong low level shear
between 30 to 45 knots. A marginal risk of severe thunderstorms
continues for the Big Sur coastline into Friday while the rest of
our region has general thunderstorms. The highest potential for
thunderstorms would be along the coastline in the late morning to
afternoon timeframe with the potential for a weak tornado or
waterspout continuing. Make sure you have multiple ways to receive
any warnings that may be issued during both the Tuesday-Wednesday
and late Wednesday-Friday systems in the event that severe
thunderstorms are able to develop. This is the most favorable
environment for severe weather that we have seen in quite a while.
Rain showers continue into Friday before diminishing heading into
the weekend. This does not mean the storm door is closing with long
range guidance showing the potential for additional systems late
December into early January.
&&
.AVIATION...
(12Z TAFS)
Issued at 442 AM PST Tue Dec 23 2025
Spotty light showers continue to move through the North Bay with
mostly mid-level clouds passing through the area. MVFR CIGs take
hold of the SF Bay, HAF, and the North Bay into the mid morning,
while other sites keep cloud cover at the mid-levels. Winds trend
southerly and southeasterly through much of the TAF period with
breezy winds arriving this afternoon and much stronger winds
expected into the late night. Showers pick up into the late day,
with increased rain rates expected to arrive overnight with the
strongest winds. Rain chances become less uniform into early
Wednesday, but shower activity will linger. Winds look to reduce
slightly into early Wednesday, but remain strong through the morning.
Vicinity of SFO...Moderate southeast winds and MVFR CIGs build in
the mid morning with some passing showers. CIGs lift into the
afternoon as winds continue to build. Gustier winds are expected in
the evening as shower activity increases. Strong southeast winds and
gusts around 40 kts will be possible in the last night as more
uniform and moderate to heavy rain affects the terminal. Winds
reduce, but still remain strong as they turn more southerly into
that morning, as showers become more spotty. Shower chances reduce
into the late morning on Wednesday as winds continue to reduce and
turn southwest.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Expect mostly mid-level clouds through the
TAF period. Moderate southerly winds build in the mid morning, and
turn southeast into the afternoon as they become breezy to gusty.
Expect strong southeasterly winds into the night as moderate showers
arrive. Winds and gusts reduce into early Wednesday, but still stay
strong through much of that morning.
&&
.MARINE...
(Today through Sunday)
Issued at 429 AM PST Tue Dec 23 2025
Winds build through the early morning with life-threatening
conditions developing across the waters. 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 and isolated storm conditions are expected again
Wednesday night into Thursday morning.
&&
.BEACHES...
Issued at 429 AM PST Tue Dec 23 2025
The strong winds along the coast will result in hazardous beach
conditions. A Beach Hazards Statement has been issued for the
coast from 4PM Tuesday through 4AM Wednesday. The main concerns
include:blowing and drifting sand and wind waves up to 20 ft. The
drifting sand and increased sea spray will also result in poor
visibilities, affecting water rescues. Increased coastal erosion
will be possible as well.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Flood Watch from 10 AM PST this morning through Friday evening
for CAZ006-508>510-512>518-528>530.
Beach Hazards Statement from 4 PM PST this afternoon through
late tonight for CAZ006-505-509-529-530.
Wind Advisory from 4 PM this afternoon 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 this afternoon to 4 AM PST Wednesday
for CAZ502-503-505-509-517-530.
PZ...Gale Warning from 9 AM this morning to 3 AM PST Wednesday for SF
Bay N of Bay Bridge.
Gale Warning from 3 PM Wednesday to 3 AM PST Thursday for SF Bay
N of Bay Bridge.
Small Craft Advisory until 9 AM PST this morning for Mry Bay-
Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60
NM-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to
Pigeon Pt 0-10 nm.
Gale Warning from 9 AM this morning to 3 AM PST Thursday for Mry
Bay.
Storm Warning from 9 AM this morning to 3 AM PST Wednesday for
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 Reyes to Pigeon Pt 0-10 nm.
Storm Warning from 9 AM this morning to 3 AM PST Thursday for
Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras
Blancas 0-10 nm.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Murdock
MARINE...Murdock
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Prepared by Boulder-Creek.com Weather at: Tue Dec 23 10:30:02 PST 2025
From the National Weather Service
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