FXUS66 KMTR 231830
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1030 AM PST Tue Dec 23 2025

...New AVIATION, MARINE...

.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...
(18Z TAFS)
Issued at 950 AM PST Tue Dec 23 2025

A few light showers are scattered across the Bay Area with
generally VFR ceilings regionally. Winds are from the south and
will increase through the day, with a dramatic increase overnight
as a strong low pressure system moves up the coast. Most terminals
will have gusts at the surface above 30 kts with strong speed 
shear likely as the low level jet moves through in the pre-dawn 
hours Wednesday morning. This storm will also bring a period of 
moderate rain with heavy downburt possible at times. There is a 
slight risk for thunderstorms, but the probability is a little too
low to include VCTS on this round of TAFs. Winds will start to 
ease mid-morning Wednesday before another push of wind, rain, and
a better chance for thunderstorms move through starting Wednesday
evening and continuing through Thursday. Some of these 
thunderstorms could be strong to severe with damaging wind gusts 
and tornados as the primary hazards.

Vicinity of SFO...The biggest question in the short term is when
the strong southerly winds will arrive. So far winds have been
much weaker than anticipated and I delayed the arrival of SE winds
exceeding 12 kts to 00Z. This was quite a change from the 15Z
arrival advertised in the 12Z TAF package. The biggest reason was
that winds remain weak and have not even become SE yet. SFO is 
still reporting gentle E to NE wind typical of weak forcing in the
early morning. While the winds may take longer to mix down to the
surface, the winds at 2,500 feet will reach 30 kts by 21Z and 
increase to 50 kts by 06Z. These strong winds aloft will likely 
cause impacts from low level wind shear. Strong southerly surface 
winds will peak around 12Z. The main band of precipitation looks 
confined to 09Z-12Z, with showers possible on either side. 
Thunderstorms are most likely from 06Z to 12Z, but the probability
remains too low to include VCTS in the TAF for now. This upcoming
storm will quickly clear out Wednesday morning as the rain stops 
and winds ease. The break won't last long as another push of 
stormy weather moves through starting Wednesday evening. Thursday
morning looks like a better chance for thunderstorms at the 
moment.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Southerly winds will increase through the
afternoon, particularly at SNS where the wind direction lines up
with the Salinas Valley. Very strong winds are expected early
Wednesday morning, when SNS may gust to a rare 50 kts. The band 
steady rain and possible thunderstorms will move through from 
around 08Z to 14Z.

&&

.MARINE...
(Today through Sunday)
Issued at 950 AM PST Tue Dec 23 2025

EXTREMELY HAZARDOUS MARINE CONDITIONS EXPECTED TUESDAY NIGHT.
Winds are currently moderate but conditions will deteriorate over
the next 12 hours. Widespread sustained gale force southerly
winds will arrive tonight with frequents gusts near 60 kts in
exposed waters. These winds will build very rough, steep waves
with a significant wave height near 20 feet. A brief reprieve
will arrive Wednesday before conditions deteriorate again
Wednesday night. If your vessel is not able to handle these
conditions return to port or seek protected waters as soon as
possible.

&&

.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 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 until 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.

     Gale Warning until 3 AM PST Thursday for Mry Bay.

     Storm Warning until 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 until 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...Flynn
MARINE...Flynn

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Prepared by Boulder-Creek.com Weather at: Tue Dec 23 14:30:03 PST 2025