FXUS66 KMTR 211757 AAA
AFDMTR
Area Forecast Discussion...UPDATED
National Weather Service San Francisco CA
957 AM PST Wed Jan 21 2026
...New UPDATE...
.KEY MESSAGES...
Updated at 245 AM PST Wed Jan 21 2026
- Late night and morning fog across the North and East Bay
Valleys
- Light rain across the Santa Lucia Range and portions of the
Central Coast late Wednesday into Thursday
- Seasonal temperatures and dry conditions Friday into next week
&&
.UPDATE...
Issued at 955 AM PST Wed Jan 21 2026
Ongoing satellite imagery reveals a shield of mid/upper level
clouds moving eastward into the area. This is ahead of an
amplifying upper low currently positioned roughly at 34.47N
127.9W. While I anticipate the radar scope will continue to
gradually illuminate through the afternoon, 12Z regional soundings
from KOAK and KVBG show a dearth of dry air below 500mb. This
will likely keep any real threat for measurable rainfall confined
to late this evening and into the pre-dawn hours on Thursday.
PoPs/Wx grids were adjusted downward through the afternoon with a
mention of sprinkles. After the 4pm-6pm timeframe, PoPs of 20-40%
are advertised which is a little on the higher end of the short-
term model consensus envelope. 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.
Otherwise, morning fog will be slow to dissipate this morning with
the mid/upper level cloud shield.
&&
.SHORT TERM...
Issued at 245 AM PST Wed Jan 21 2026
(Today and tonight)
High clouds are currently obscuring lower level fog development but
a few reports have started trickling in from the East Bay in
Byron and Concord. As of 2AM, Byron is reporting less than 1/4SM
visibility and fog while the Concord Airport is reported 1/4SM
visibility and fog. There are some signs of fog developing in the
North Bay Valleys with the Santa Rosa Airport reporting low clouds
and 1SM visibility. Fog coverage tonight should be similar to
last night with patchy, locally dense fog expected in the North
and East Bay Valleys. Early morning commuters in these areas
should allow extra time to reach their destination and be prepared
for sudden changes in visibility.
The upper level ridge that has been dominating our forecast for
the last few weeks will be replaced by a cut-off low moving
southwards down the California coastline today. The cut-off low
will bring a few notable changes to our weather. The first is
temperatures across the interior will return to cooler, more
seasonal values with highs in the upper 50s to low 60s across the
region. Morning low temperatures are expected to be in the low 40s
to upper 40s with the higher elevations remaining in the upper
40s to low 50s.
The second change will be increased rain chances late Wednesday
into Thursday for the Central Coast. High resolution models are
showing isolated showers starting late this evening into Thursday
morning across the Santa Lucia Range, the Monterey Peninsula, and
portions of interior San Benito County. Now, if any rain is able
to make it to the surface, any precipitation totals are expected
to be low. The current forecast grids show less than 0.10" of
accumulated precipitation across the Central Coast. 90th
Percentile NBM guidance (a reasonable "worst case" scenario) shows
between 0.1-0.35" across the Central Coast with the max in the
Santa Lucia Range. While showers are most likely to impact the
Central Coast, we may see a few isolated showers as far north as
Santa Cruz County and the South Bay. The NBM places a less than 5%
chance of thunderstorms across southern coastal Monterey County
with atmospheric conditions looking unfavorable for thunderstorm
development. Models do show between 100- 300 J/kg of most unstable
CAPE but thunderstorm potential is limited by poor moisture, poor
shear, and poor 700-500mb lapse rates. The most likely scenario
is that we will see isolated showers across the Central Coast,
predominantly in the Santa Lucia Range, with the potential for
isolated showers to drift towards the South Bay on Thursday.
&&
.LONG TERM...
Issued at 245 AM PST Wed Jan 21 2026
(Thursday through Tuesday)
Isolated showers continue across the Central Coast through Thursday
morning before dry weather returns. By late Thursday, the cut-off
low will be to our southeast (offshore of San Diego and Baja
California) where it will move inland and be absorbed into upper
level troughing across the interior U.S. late Friday into early
Saturday. Upper level ridging then rebuilds across the western
U.S. through the remainder of the long term forecast. Widespread fog
potential decreases by late this week as a shallow marine layer
(approx. 1000 ft) is able to redevelop as the cut-off low moves
through. Overcast conditions are still likely as low level stratus
and the shallow marine layer rebuild across the region.
High temperatures remain seasonal in the upper 50s to low 60s while
portions of the interior Central Coast linger in the low to mid 60s.
Morning low temperatures trend cooler starting Thursday with lows
dropping from the 40s on Thursday to upper 30s to low 40s by
Saturday. Sunday to Tuesday mornings look to be the coldest with
lows dropping into the mid 30s to low 40s across the interior.
Locally gustier offshore winds develop across the interior North Bay
Saturday. Probabilistic guidance shows a 30-40% chance of gusts
greater than 30 mph across the North Bay Interior Mountains. This
drops to a 10-25% chance across only the highest peaks when looking
at the probability of gusts greater than 40 mph. While this is a
gustier offshore wind event, it should generally stay limited to the
higher terrain.
In the very long term, models continue to indicate a chance for
widespread precipitation to return late January into early
February. The CPC 8-14 day outlook shows a slight chance for above
normal precipitation along coastal Sonoma and Marin Counties with
near normal precipitation expected for the rest of the Bay Area
and Central Coast. Models will come into better agreement as to
the timing and intensity of any future systems as we get closer in
time to late January so stay tuned to the forecast to see how
this shapes up in real time.
&&
.AVIATION...
(18Z TAFS)
Issued at 933 AM PST Wed Jan 21 2026
Fog and stratus persist over the North and East Bay valleys with mid-
to high level clouds delaying the mixing out process. Have opted to
go with a more persistent forecast for STS mixing out, and a later
forecast for APC mixing out, although this is a low confidence
forecast and it is possible STS and APC remain socked in through the
day. Greater confidence in lingering fog and stratus impacts in the
far interior East Bay and areas near the Delta, including CCR. The
rest of the region should expect generally VFR conditions and mid-
to high level cloud cover through the daytime hours. Winds remain
light through the TAF period. Overnight, fog and stratus should
develop across the North and East Bay valleys, with moderate
confidence for development along the immediate coast. High
resolution model data shows some stratus developing in the San
Francisco Bay Area, but this is a low confidence forecast at this
time and lingering high clouds may limit the impact of radiational
cooling processes, lowering the chances for overnight stratus. Along
the Central Coast, some isolated showers are possible along the
Santa Lucia range overnight into Thursday morning.
Vicinity of SFO... VFR through the day. High resolution model output
is attempting to place stratus across the East and South Bays, but
impacts to SFO are lower confidence. Considered a SCT group at SFO
to convey the uncertainty, but opted to hold off at this time as
the area of greatest confidence seems tilted towards OAK and SJC.
Winds remain light with offshore flow lingering through the morning
until mild onshore flow develops this afternoon.
SFO Bridge Approach... Similar to SFO.
Monterey Bay Terminals... VFR with mid- to high level clouds through
the day. This evening and overnight, low stratus develops at the
terminals with isolated showers possible across the Santa Lucia
range, low to moderate confidence for impacts to the terminals.
Winds remain light through the TAF period with drainage winds
overnight and through the morning, and onshore flow in the afternoon
and evening.
&&
.MARINE...
(Today through Monday)
Issued at 933 AM PST Wed Jan 21 2026
Gentle to moderate northerly breezes and moderate seas persist
through Thursday. On Friday, winds will increase to a fresh
northerly breeze along with building rough seas. 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...None.
&&
$$
SHORT TERM...Kennedy
LONG TERM....Kennedy
AVIATION...DialH
MARINE...DialH
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Prepared by Boulder-Creek.com Weather at: Wed Jan 21 12:30:03 PST 2026
From the National Weather Service
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