FXUS66 KMTR 121125
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
325 AM PST Fri Dec 12 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1214 AM PST Fri Dec 12 2025
- Hazardous beach conditions today
- Tule fog and stratus continue for the North and East Bay
- Wetter pattern expected next week
&&
.SHORT TERM...
Issued at 1214 AM PST Fri Dec 12 2025
(Today and tonight)
The same general pattern persists dominated by a slow moving ridge,
light offshore flow, and persistent stratus and fog focused on
the North and East Bay valleys. The strong temperature inversion
and offshore winds are creating adiabatically warmed winds along
the coast and nice beach weather. Sunny Half Moon Bay reached 72
degrees today and spent roughly 7 hours in the 70s. Meanwhile,
thick fog continued to impact the San Pablo Bay region, and San
Rafael only made it to 48 degrees. It's not often that Half Moon
Bay is 24 degrees warmer than San Rafael, outside of the last few
days anyway. I hate to say it again, but Friday will be more of
the same. The stratus looks like it will be slightly less
expansive and the South Bay will be the biggest benefactor of
this change. We're continuing to add a persistence nudge to the
forecast to help capture the wide range of max temperatures we've
seen across the region recently.
&&
.LONG TERM...
Issued at 1214 AM PST Fri Dec 12 2025
(Saturday through Thursday)
The long range trend is a gradual shift away from this prolonged dry
period to a more active, wetter pattern. The end is finally in sight
for this ridiculously resilient ridge we've been dealing with
since December 4th. The ridge axis will finally slide to our East
on Saturday. We'll still likely have the Tule fog impacts through
the weekend, but the pattern shift will be felt with slightly
cooler temperatures in the sunny areas. The change will be subtle
though as we remain in backside of the ridge through Monday. The
500 mb flow becomes zonal in the middle of the week. This new
pattern, combined with a plume of 1.2"+ PW should bring some light
rain from Tue-Wed, focused on the North Bay. The more active
zonal pattern will transition to a low-amplitude ridge Thursday-
Friday, although some light rain is still possible with lingering
high PW. The most interesting part of the forecast is the
following weekend. It's looking more and more likely that a deep
trough and associated high moisture plume will bring an
Atmospheric River to the Bay Area. The Climate Prediction Center
now has a moderate risk of both heavy precipitation and high winds
across the Bay Area and Central Coast from 12/19-12/22. December
is typically the wettest month for San Francisco, where the normal
monthly rainfall for is 4.76". While we haven't had any rain
since 11/20, the upcoming sequence will start to chip away at this
deficit and there is more rain possible the following week. Long
range ensembles show about a 25% chance of getting 3+" between now
and the 26th.
&&
.AVIATION...
(12Z TAFS)
Issued at 318 AM PST Fri Dec 12 2025
Tule fog continues to blanket the Central Valley, Sacramento River
Delta, and the North Bay and East Bay valleys. LVK, STS, and APC
will certainly be dealing with ceiling and visibility impacts
through the morning. SJC has stayed clear so far, but the
temperature has dropped to 39F with a 38F dew point, indicating
radiation fog will soon form. All terminals should clear in the
afternoon with a similar timing as seen yesterday.
Vicinity of SFO...Only a 20% chance of developing IFR ceilings or
fog. Even if these conditions materialize, the impacts should be
brief, as observed yesterday. Otherwise winds will favor a NE
direction and remain gentle all day.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...Light offshore flow will keep the skies
clear all day. There is a slight chance for impacts Saturday
morning as a weak southerly surge may develop and bring stratus up
the Central Coast.
&&
.MARINE...
(Today through Wednesday)
Issued at 318 AM PST Fri Dec 12 2025
Gentle NE winds will gradually shift to southerly by Saturday as
moderate to rough seas subside to a slight 3 feet from Saturday
through Monday. These favorable conditions are rare for winter. A
moderate westerly swell will return by Tuesday with moderate
westerly winds arriving Wednesday.
&&
.BEACHES...
Issued at 1214 AM PST Fri Dec 12 2025
Long period NW swell is causing hazardous beach conditions
Friday. This energy brings strong rip currents, an increased risk
for sneaker waves, and large breaking waves. This coincides with
nice warm weather, which will likely lure more people to the beach
under a false sense of security. A Beach Hazard Statement is in
effect through Friday evening. Respect the power of the ocean and
never turn your back on it.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement through this evening for CAZ006-505-509-
529-530.
PZ...None.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Flynn
MARINE...Flynn
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Prepared by Boulder-Creek.com Weather at: Fri Dec 12 06:30:02 PST 2025
From the National Weather Service
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