FXUS66 KMTR 210516
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
916 PM PST Tue Jan 20 2026
...New AVIATION, MARINE...
.KEY MESSAGES...
Updated at 1225 PM PST Tue Jan 20 2026
- Late night and morning fog across the North and East Bay
- Light rain across the Santa Lucia Range Late Wednesday into
Thursday
- Mild and mostly rain-free for the Bay Area and Central Coast
&&
.UPDATE...
Issued at 606 PM PST Tue Jan 20 2026
Overcast skies will continue through the day Wednesday, keeping
temperatures mild. There's a slight chance for drizzle or very
light rain through the day as the cut-off low approaches the
coast. Most of the precipitation will evaporate before it reaches
the ground, but don't be surprised to see a few drops here and
there before the low moves south and the clouds start to break up
Thursday.
&&
.SHORT TERM...
Issued at 1225 PM PST Tue Jan 20 2026
(This evening through Wednesday)
Fog continues to gradually dissipate across the region as
mid/upper level moisture continues to lift northward. While the
cloud shield is expansive, examination of our morning sounding and
aircraft sounding data from SFO reveals that the low levels
remain quite parched. What this translates to is high confidence
that widespread rainfall is unlikely over the short term.
The primary hazard in the short term will be the re-development
of fog, largely across the North and East Bay. While mid-level
ridging remains in place across the area, surface flow will
gradually become more southerly which may support more in the way
of onshore flow. At a minimum, this should promote fog development
in the favored spots of the North and East Bay, if not give us a
higher chance. In fact some of the higher resolution model
guidance advertises a repeat of fog across the US HWY 101 corridor
across Sonoma County, similar to today.
&&
.LONG TERM...
Issued at 1225 PM PST Tue Jan 20 2026
(Wednesday night through next Monday)
While general mid/upper level ridging will equate to a largely
"quiet" long term forecast period, there will be some brief shifts
in the main upper pattern (in addition to morning fog). These
shifts will offer slight changes in the day to day sensible
weather elements. Late Wednesday into Thursday, model guidance is
a bit more honed in on the exact track of an upper low forecast
to intensify and move eastward through Southern California. This
will induce upslope flow across the higher terrain of the Central
Coast. While moistening will transpire, it doesn't appear that the
column will completely saturate for a prolonged period of time.
In addition, the speed of this upper trough will mean a low
residence time across our area. At this time, there doesn't appear
to be a significant amount of spread in the track of this feature
so confidence is high that overall rain amounts will remain on
the light side through Thursday night. In fact, some of the
higher end scenarios (90th percentile) paint up to a tenth of an
inch of rainfall for this event.
By Friday evening/Saturday morning the main upper low will kick
eastward. In the wake of this system, a more defined push of
offshore winds is anticipated. At this juncture, the potential for
winds above 35 mph is under 10%, though it may be a little higher
across some of the favored gaps and passes. The story will be a
little different across the marine zones as the surface pressure
gradient does tighten. In fact 925mb flow does ramp up here to
around 35 knots (40 mph) across Pacific waters west of
Marin/Sonoma counties.
Beyond day 7, model guidance remains largely consistent with broad
ridging remaining in place. At times, however, storm systems may
attempt to dampen out the amplitude of the ridge and place our
region within a more zonal pattern. Some of the ensemble guidance
systems remain aggressive with rainfall above 1/2." While the upper
air pattern depiction is largely similar from ensemble suite to
ensemble suite, the spread among individual systems (e.g., EPS)
remains rather high as the spread ranges from no rain to three
inches of rain in some locales. As always, we'll continue to
monitor, message, and adjust as necessary.
&&
.AVIATION...
(06Z TAFS)
Issued at 900 PM PST Tue Jan 20 2026
High overcast skies will persist through the TAF period with some
patchy fog developing at the North Bay terminals through the
early morning hours. There is a slight chance for very light
precipitation through the day Wednesday, but not enough to impact
the visibility. Winds will remain light through the night with a
gentle onshore breeze developing Wednesday afternoon.
Vicinity of SFO...VMC expected to persist through the TAF period
with a light easterly breeze. There is a very slight chance for
mist to develop around sunrise, but the confidence is far to low
to include anything more than a 6SM BR hint in the TAF.
SFO Bridge Approach...A high overcast layer will gradually lower
through the day, but should remain above 8,000 feet through the
TAF period.
Monterey Bay Terminals...VMC expected to persist through the TAF
period with gentle winds and gradually lowering high clouds.
These terminals have the best chance for light rain Wednesday, but
there shouldn't be any impact to visibility either way.
&&
.MARINE...
(Tonight through next Monday)
Issued at 900 PM PST Tue Jan 20 2026
A gentle to moderate northerly breeze and moderate seas will
continue through Thursday. On Friday winds will increase to a
fresh northerly breeze, building rough seas. Conditions will
improve over the weekend as a light to gentle breeze settles in
and seas gradually subside to slight Sunday - Monday.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&
$$
SHORT TERM...Bain
LONG TERM....Bain
AVIATION...Flynn
MARINE...Flynn
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Prepared by Boulder-Creek.com Weather at: Tue Jan 20 22:30:03 PST 2026
From the National Weather Service
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