FXUS66 KMTR 220011
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
411 PM PST Wed Jan 21 2026

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 116 PM PST Wed Jan 21 2026

 - Morning fog across North Bay and East Bay Valleys

 - Sprinkles or very light rain tonight into Thursday morning
   across the Central Coast and portions of the Bay Area

 - Increased offshore wind potential across higher terrain of the
   North Bay late Friday into Saturday

&&

.SHORT TERM...
Issued at 116 PM PST Wed Jan 21 2026 
(This afternoon through Thursday)

Generally quiet with largely mild conditions this afternoon 
across the Bay Area and Central Coast. Fog continues to slowly
erode at this hour, with predominantly mid/upper level clouds 
continuing to overspread the area. Our upper low continues churn 
and WV/RAP mesoanalysis trends indicates that it continues to make
it slow trek to the south and east. This is in line with current 
thinking. Radar imagery this afternoon has shown a couple of brief
attempts at a loosely organized bands of what is largely 
virga/fall streaks. While the trends haven't been encouraging, 
satellite imagery indicates still some mid-level cumuliform 
clouds/instability that may swing to the NE and give us another 
shot as sprinkles or very light rain after 4pm this evening and 
continuing through the pre-dawn hours on Thursday and this seems
in alignment with latest short term guidance. As noted this 
morning, PoPs of 20-40% are advertised which remains along the 
higher end of the near/short term hi-resolution model guidance. Rain
amounts at this time are anticipated to average around a few 
hundredths of an inch with the higher end scenario (10% chance of 
occuring) advertising a larger QPF footprint (light rain as far as
the North Bay) and up to a tenth of an inch across the higher 
terrain of Central Coast. 

As the main upper low continues to pivot eastward, subtle 700mb 
WAA may lift northward through the Central Valley and into the
North Bay. While some orographic ascent cannot be ruled out along
the eastern slopes of higher terrain, the dry low levels should
translate to a low probability for measurable precipitation here,
even though radar may look rather ominous.

Otherwise, fog, albeit limited due to the cloud cover, may 
continue overnight and into early Thursday morning. However, 
additional low level mixing thanks to the elevated wind field make
keep the footprint smaller than previous nights.

&&

.LONG TERM... Issued at 116 PM PST Wed Jan 21 2026 
(Thursday night through next Tuesday)

Thursday evening will feature a subtle PV anomaly will ripple 
through the Great Basin and help sweep the initial upper low 
eastward. In its' wake, mid/upper level ridging is forecast. This
will promote surface pressure rises across the Great Basin and 
tighten local MSLP gradients across the region. More importantly,
the 925mb flow will increase with even coarser guidance 
advertising 30-40 knots out of the north through the Sacramento 
Valley. 

The synoptic scale background/pattern recognition in tandem with 
the Extreme Forecast Index (EFI) would suggest an opportunity to 
alter messaging to advertise a noticeable uptick in winds, largely
across the higher terrain of the North Bay and East Bay Hills. 
2km PG&E WRF cross sections also indicate the potential for 
mountain wave type activity near and downwind of Mt. Saint Helena 
which could help enhance wind gusts. Given the highly localized 
nature of these phenomenon, have opted for targeted edits across 
the Mayacamas and higher terrain of the East Bay such that wind 
gusts reflect a blend of some of the higher end NBM percentiles. 
While fuel moistures have dried some, ERC values remain safely 
below critical fire weather thresholds. That said, please always 
be mindful that winter fuels could still promote some fire 
growth/smoke production. 

Overall, the themes in the extended forecast have not changed 
much. Ridging is anticipated to resume this weekend and largely 
dominate the weather pattern across the region through the early 
to middle part of next week. Thereafter, about one-quarter of the 
multi-model ensemble advertises more vigorous troughing across the
Pacific NW. This would dampen out the ridge such that mid/upper 
level flow becomes more southwesterly, potentially opening the 
door for a disturbance or two. While the official forecast paints
broad PoPs across most areas (minus the far interior Central 
Coast), there still remains some model variability with some NWP 
"clusters" indicating little to no chance for precipitation. We'll
continue to delve deeper into the model guidance with time. 

&&

.AVIATION...
(00Z TAFS)
Issued at 334 PM PST Wed Jan 21 2026

Expect VFR conditions for the remainder of the afternoon and
evening for all terminals. Later tonight through early Thursday morning
there is chance for MVFR/IFR ceilings to develop, however 
confidence is low in the exact timing and extent. Low stratus is 
possible for terminals closer to the coast with weak onshore flow 
at times. Fog is expected to develop in the North Bay, however hi-
res guidance has a weaker signal than previous few days. 

Vicinity of SFO...Weak onshore flow may result in low stratus
developing overnight into early Thursday morning, however the
winds will be light and occasionally offshore, thus chances seem
too low for dropping cigs into MVFR for the TAF.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Expect VFR for the remainder of the
afternoon and evening. Weak onshore flow is expected to become 
offshore once again later tonight as an offshore upper level 
disturbance passes to the south. There is a chance for some brief 
periods of light rain as well when MVFR cigs may develop. 
Steadier but still weak onshore flow returns late in the TAF 
period.

&&

.MARINE...
(Tonight through next Monday)
Issued at 334 PM PST Wed Jan 21 2026

Gentle to moderate northerly breezes and moderate seas persist
through Thursday morning. On Thursday afternoon into Friday,
winds will increase to a fresh northerly breeze along with
building rough seas. Strong to near gale force gusts will create
hazards for small craft across the northern outer waters, with
gale force gusts possible in the far northern outer waters.
Conditions will improve over the weekend as a light to gentle
breeze settles in and seas gradually subside to slight Sunday
through Monday.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...Small Craft Advisory from 3 PM Thursday to 9 PM PST Friday for 
     Pt Arena to Pt Reyes 10-60 NM.

&&

$$

SHORT TERM...Bain
LONG TERM....Bain
AVIATION...JM
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Wed Jan 21 18:30:03 PST 2026