FXUS66 KMTR 201150
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
350 AM PST Tue Jan 20 2026
...New AVIATION...
.KEY MESSAGES...
Updated at 309 AM PST Tue Jan 20 2026
- Dry weather, cool mornings, and mild afternoons this week
- Morning fog across the Delta, North Bay Valleys, and interior
East Bay Valleys
- Low potential for scattered showers across the Santa Lucia
Range late week
&&
.SHORT TERM...
Issued at 309 AM PST Tue Jan 20 2026
(Today and tonight)
A ridiculously resilient ridge continues to dominate our short term
forecast. The main short term edit was to bump up dense fog
potential for the North and East Bay Valleys and to lower forecast
morning temperatures for the interior valleys by a few degrees.
There is some indication that fog is forming along the North and
East Bay Valleys and San Pablo Bay/Delta region. As of 2:30AM the
Napa County airport is reporting a visibility of 3/4SM, the
Petaluma Airport is reporting 1 1/2SM, and Byron is reporting less
than 1/4SM visibility and dense fog. Early morning commuters in
the North and East Bays should be prepared for sudden changes in
visibility and allow extra time to reach their destinations.
We can expect temperatures to be slightly cooler today compared to
yesterday as the upper level ridge starts to break down and a cut-
off low approaches the West Coast. Ahead of the cut-off low, we
are starting to see some cold air advection which is resulting in
a slight cooling trend. To contextualize this, the 00Z sounding
recorded an 850 mb temperature of -13.6 C. Model guidance shows
850 mb temperatures gradually cooling to around 10C by early
Wednesday and cooling further Wednesday into Thursday as the cut-
off low arrives. The cooling trend will be most noticeable across
the higher elevations where temperatures will drop from the 70s
back into the mid 60s. For Tuesday, temperatures across the Bay
Area will generally be in the low to mid 60s while temperatures
across the Central Coast will be in the mid 60s to low 70s. Expect
another round of fog tonight into tomorrow morning across the
North and East Bay Valleys.
&&
.LONG TERM...
Issued at 309 AM PST Tue Jan 20 2026
(Wednesday through Monday)
The upper level ridge will continue to break down Wednesday into
Thursday as a cut-off low approaches the West Coast. This cut-off
low will move down the coast of California Thursday and Friday
before being absorbed into an upper level trough over much of the
United States. As the low moves down the coastline, it will bring a
surge of slightly moister air (PWAT values around 1") to southern
California. This moister air will clip southern Monterey County and
bring a slight potential for showers in the Santa Lucia Range. The
current forecast grids have a 10-20% probability of precipitation
across the southern coastal waters and southern Monterey County late
Wednesday into early Thursday. No real accumulation is expected from
this system as the bulk of the moisture (and rain) will be well to
our south. Ridging rebuilds over the West Coast by late
Saturday/early Sunday and remains in place into next week. The next
chance for widespread rain still looks likely end of
January/beginning of February with models consistently showing a
deep upper level trough moving into the West Coast. Worth noting
that ECMWF ensemble members have started gaining confidence with
nearly every member showing at least some precipitation during that
timeframe. There's still a wide range in timing and amounts so we'll
have to see how this shapes up as it gets closer.
Temperatures remain seasonal through the long term forecast with
highs in the upper 50s to low 60s Wednesday through Monday. The
exception will be for the interior Central Coast which will see a
slight warming trend into the mid to upper 60s starting Saturday.
Overnight low temperatures generally stay in the 40s for much of the
long term but some locations do drop into the upper 30s again
starting Saturday. Winds remain light through the forecast period
with fog likely overnight Wednesday. There is some potential for
more widespread fog Thursday and Friday nights but current thinking
is leaning more towards the return of stratus over fog. Model
guidance shows the marine layer deepening to around 1000 ft
starting Thursday which would support the return of stratus to the
interior. Either way, the potential for degraded visibility and
potential to impact morning commutes will continue for much of the
upcoming week. Anyone driving early in the morning should be
prepared in the event they encounter fog and experience a sudden
drop in visibility.
&&
.AVIATION...
(12Z TAFS)
Issued at 339 AM PST Tue Jan 20 2026
Largely still a persistence forecast with a couple of slight
caveats. For terminals along the Delta (incl. KAPC), Tule fog is
making a bigger impression this morning, along with stronger
offshore winds. The fog will likely mix out through this morning
over areas of western Solano and Contra Costa counties. However,
higher than usual easterly offshore winds look to persist through
much of today. Otherwise VFR across the board with some slight
reductions in VIS along coastal areas thanks to more BR in the
air.
Vicinity of SFO...Still looking at light winds with a slight NE
component through the mornings. Looking at a bit higher chance of
reduced VIS this evening, but low confidence holds back any
further sig reduction in flt cat noted in TAF.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR. Most notable change with this TAF
issuance is the potential reintroduction of marine stratus along
the coast from MRY peninsula to Central Coast by the end of this
TAF period. Confidence low in impacts to terminals, but there are
at least some hints at low cloud decks into Wednesday morning.
&&
.MARINE...
(Today through Sunday)
Issued at 309 AM PST Tue Jan 20 2026
Gentle to moderate breeze continues across the waters early this
week. Winds increase late week to a strong breeze by Friday. Weak
storm system over the eastern Pacific will result in moderate
northwest swell as well, promoting rough seas across the northern
outer waters.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...Behringer
MARINE...Behringer
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Prepared by Boulder-Creek.com Weather at: Tue Jan 20 08:30:03 PST 2026
From the National Weather Service
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