FXUS66 KMTR 080549
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
949 PM PST Sun Dec 7 2025
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1218 PM PST Sun Dec 7 2025
- Benign conditions through the next seven days with no
precipitation expected and a gradual warming trend through the
later part of the week
- Impacts from Tule Fog continue in the North Bay and interior
East Bay valleys, with potential for expansion across the rest
of the Bay Area overnight
- Next chance for rain lies slightly beyond the 7-day outlook
&&
.UPDATE...
Issued at 842 PM PST Sun Dec 7 2025
Widely varying weather continues with the North Bay and the East
Bay catching much of the Central Valley's fog, stratus and sun
blocked and chilled air arriving on light offshore winds. The
forecast is near persistence tonight and Monday. To the south
across the rest of the Bay Area and including the north Central
Coast the sky has been hazy otherwise mainly clear and somewhat
milder. Cirrus clouds will move out of the area tonight with the
ECMWF layer humidity forecasts showing cirrus free nights for the
next several nights at least. In summary: a stable air mass, low
sun angle heat input, longer night-time cooling hours, light winds
and trapped air pollutants all favor the current feedback loop of
aforementioned fog, stratus, hazy to haze conditions and sun
blocked and chilled air.
The northern extent of broad and strong 500 mb subtropical high
pressure ridging remains over the forecast area. We remain stuck
with high pressure and dry weather since the larger scale north
hemispheric long wave trough pattern contracted after an early
and strong start to the rain season. It's now been over two weeks
since our last measurable rain and there's no current indication
of a weakening of the ridge at least through this week.
&&
.SHORT TERM...
Issued at 1218 PM PST Sun Dec 7 2025
(This evening through Monday)
Today is looking to be very similar to yesterday, right down to the
satellite imagery showing outgrowth from the Tule Fog across the Bay
Area, slowly dissipating south of the Golden Gate and west of the
Berkeley-San Leandro Hills and the eastern Santa Clara Mountains,
and lingering across the North Bay and interior East Bay valleys.
Indeed, if you compared the current satellite image and the one from
yesterday, you could only them apart by the lack of coastal stratus
today. As a point of curiosity, while there are no radiosonde
observations over the Central Valley, aircraft soundings from the
region suggest that the saturated lower atmosphere -- the "Tule fog"
layer, if you will -- extends 1500-2000 feet above the ground. The
Central Coast remains mainly clear.
The remarkably similar evolution of the stratus from yesterday
through today has lowered confidence in the clearing of stratus from
the Santa Rosa Plain and the rest of the North Bay valleys. I've
tamped down the high temperatures today even further in those
regions, into the upper 40s to the lower 50s, and even then the
expected highs are still a little warmer than the observed highs
yesterday. Across the rest of the region, temperatures range from
the middle 50s to lower 60s across the Bayshore, the Bay Area
Pacific Coast and the Santa Clara Valley, while the sun-blessed
Central Coast sees highs in the lower to middle 60s in the Monterey
Bay region and the Hollister area, and the upper 60s to lower 70s
inland.
Tomorrow, the ridge over the West Coast will strengthen and continue
a general warming trend across the region. For the Central Coast,
the temperature forecast should be similar to today's. The
uncertainty increases across the Bay Area and especially in the
North and East Bays, where the impacts of the building ridge on the
Tule Fog remain uncertain. In general, a building ridge will tend to
compress the inversion layer, and limit the extent that the Tule Fog
can extend across the region. (We see this happen during our marine
layer season as well, when building ridges compress the marine layer
and prevent it from coming inland.) If the inversion layer does
compress enough, the Tule Fog could find itself hitting a proverbial
wall before it reaches the Bay Area. On the flip side, for those
areas still impacted by the Tule Fog, ceilings and visibilities will
tend to drop. This makes the temperature forecasts highly uncertain.
For now, tamped down the temperatures slightly so that the North and
East Bay valleys see highs in the middle 50s to lower 60s, while the
rest of the Bay Area valleys see highs in the lower to middle
60s, but this might be quite optimistic indeed.
&&
.LONG TERM...
Issued at 1218 PM PST Sun Dec 7 2025
(Monday night through next Saturday)
Ridiculously resilient ridging will dominate the weather pattern
through the rest of the week with the ridge crawling through the
Western United States, such that over the next 6 days the ridge axis
moves from just off the coast of the Pacific Northwest to the Oregon-
Idaho border area. Over the Central Coast the impacts are most
certain with a gradual warming trend in the forecast. The warmest
days are expected Wednesday through Saturday with highs reaching the
upper 60s to the middle 70s across the inland valleys. The Bay Area
in general and the North and East Bay valleys in particular remain
tied to the evolution of the Tule Fog. Impacts are expected to
persist into the early part of the work week before diminishing with
the continuing ridging across the region.
The pattern change for the middle of the month is beginning to come
into the very end of the 7 day outlook. The early indications are
pointing more towards a zonal flow pattern for the Western United
States and any rain storms that develop generally being deflected
into the Pacific Northwest. Beyond the 7-day outlook, the ensemble
model clusters suggest that a return to a wetter pattern is possible
around 9-10 days out, and the CPC's 8-14 day outlook shows a slight
lean towards rainfall totals above seasonal averages for the third
week of December. I have heard that before this month...
&&
.AVIATION...
(06Z TAFS)
Issued at 948 PM PST Sun Dec 7 2025
Low clouds and fog are building in the North Bay and interior East
Bay, but have cleared over STS and LVK while APC remains IFR. Expect
cloud cover to lower further into the night while the fog to becomes
thicker. The OAK and SJC see CIGs arrive overnight with some
reductions in visibilities. Winds stay mostly light to moderate
through the morning, with wind directions determined by more
localized affects. Cloud cover and fog will be slow to erode into
Monday, but conditions look to improve into the afternoon. However,
the North and East Bay will continue to struggle with low clouds and
fog, causing some doubt for clearing at STS and LVK, while APC
doesn't clear. As cloud cover erodes, pockets of haze will affect
much of the region. CIGs and fog reform for STS and APC into the
evening.
Vicinity of SFO...VFR through the TAF period. Winds become lighter
into the night with scattered low clouds building into the area,
along with some slight reduction in visibilities. Cloud cover thins
into the afternoon and winds become slightly more moderate and
northwesterly.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR through the TAF period. Winds stay
light for MRY through the TAF period, while SNS sees moderate
northwest winds become light into the night. North to northwest
winds return Monday afternoon with the potential for haze.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 948 PM PST Sun Dec 7 2025
Moderate to fresh north to northwest winds continue for the
southern waters. Moderate seas with wave heights 6 to 8 feet
across the outer waters will subside to around 4 to 6 feet for
Monday. Winds and swell increase Monday night, with strong gusts
possible across the waters. A new, long period northwesterly
swell is anticipated by Wednesday and looks to exit late Friday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory until 9 AM PST Tuesday for Pt Pinos to Pt
Piedras Blancas 0-10 nm.
Small Craft Advisory from 3 PM Monday to 3 AM PST Tuesday for Pt
Arena to Pt Reyes 10-60 NM.
Small Craft Advisory from 3 PM Monday to 9 AM PST Tuesday for
Pigeon Pt to Pt Pinos 10-60 NM.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Murdock
MARINE...Murdock
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Prepared by Boulder-Creek.com Weather at: Mon Dec 8 00:30:02 PST 2025
From the National Weather Service
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