FXUS66 KMTR 181702
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
902 AM PST Sun Jan 18 2026

...New AVIATION...

.KEY MESSAGES...
Updated at 1206 AM PST Sun Jan 18 2026

 - Dry weather, cool mornings, and warm afternoons this week 

 - Morning fog possible across the Delta and interior valleys

&&

.UPDATE...
Issued at 837 AM PST Sun Jan 18 2026

Seeing less fog coverage this morning across the North Bay Valleys, 
yet in the interior East Bay Valleys and Delta we are seeing similar 
conditions as yesterday morning. As of this writing, both Concord 
and Byron airports are reporting visibilities of less than 1/4 mile. 
In addition, mid to high level clouds continue to stream across the 
region. With day time heating, fog is forecast to lift and mix out 
by early afternoon across the East Bay. Otherwise, no updates are 
anticipated at this time as the forecast remains on track. 

&&

.SHORT TERM...
Issued at 1206 AM PST Sun Jan 18 2026
(Today and tonight)

High clouds continue to blanket the Bay Area and Central Coast 
tonight. These elevated moisture is concentrated between 27,000 and 
37,000 ft. The main impact of these clouds is reducing radiational 
cooling to space. They do this indirectly by absorbing and re-
emitting thermal energy back to the surface. Valley temperatures are 
between 1-5 degrees warmer than this time last night. However this 
degraded cooling hasn't been enough to stop the Tule Fog from 
forming in the Central Valley. Dense fog is being reported from 
Sacramento to Hanford, including the Sacramento River Delta and 
surrounding areas. Concord has been reporting dense fog for several 
hours, but no other airports in our cwa have joined in. The SFO-WMC 
gradient is -8.2 mb, substantially weaker than 24 hours ago. This
is bringing much lighter offshore winds, with Mt. St. Helena now 
gusting around 5 mph, vs nearly 50 mph last night. Outside of the 
weaker mountain winds, today will be nearly identical to 
yesterday. Expect a crisp morning with some localized fog, 
colorful sunrise thanks to high clouds, warm afternoon with 
filtered sunshine, and another great sunset. Enjoy the weather 
today, it doesn't get much better this time of year. 

&&

.LONG TERM...
Issued at 1206 AM PST Sun Jan 18 2026
(Monday through Saturday)

The ridge is gradually weakening, but nice weather will continue
in the long term period. The 500 mb height is continuing to very 
slowly lower following the near record of 5,900 m last Wednesday. 
This trend will continue through the week, and it's expected to 
fall below 5,700 m by Friday. That's near the daily average for 
this time of year. A similar story is unfolding with the 850 mb 
temperature, dropping from near record territory to near normal by
the end of the week. This is being caused by a trough over the 
North Central Pacific spitting out a cut-off upper level low late 
this week. All indications are that this system will have a very 
weak surface reflection and will stay offshore through the 
weekend, but it will take a bite out of the ridge. While it's 
still possible for a few drops to fall, the trend has been clear 
that this system will not bring significant rain to the cwa. It 
will, however, serve as a catalyst to usher in a more active 
pattern the following week, which could bring us some long- 
awaited rain for the last few days of the month.

&&

.AVIATION...
(18Z TAFS)
Issued at 902 AM PST Sun Jan 18 2026

Fog and stratus continues to mix out across the North and East Bay 
valleys with lingering impacts at CCR for the next couple of hours, 
but the TAF sites remain VFR through the day. Winds will remain 
light to gentle with a weak onshore breeze near the coast and 
offshore winds persisting inland. Fog and stratus return to the 
North and East Bay valleys tonight with haze expected at LVK. High 
resolution model data depicts some chance for stratus development in 
the San Francisco Bay, but this is a low confidence forecast at this 
time.

Vicinity of SFO... VFR through the day. High resolution model output 
is attempting to place a patch of stratus within the San Francisco 
Bay, but impacts to the terminal are highly uncertain and opted to 
leave the VFR TAF intact for now. Chances for stratus diminish after 
18-21Z on Monday morning. Winds remain light with offshore flow 
predominant through the afternoon until mild onshore flow develops 
late this evening.

SFO Bridge Approach... Similar to SFO.

Monterey Bay Terminals... VFR through the TAF period. Light westerly 
winds through the afternoon and evening, with breezy valley drainage 
winds developing overnight.

&&

.MARINE...
(Today through Friday)
Issued at 837 AM PST Sun Jan 18 2026

Gentle to moderate northeast to east breezes continue across the
San Pablo Bay, the Delta, and through the Golden Gate through
Wednesday while light to gentle northeast to north winds continue
across the rest of the coastal waters. Later this week, the ridge
should break down as a weak cutoff low approaches, allowing winds
to increase and shift to the northwest and west. Low seas up to
around 6 feet continue through the middle of the week as a
northwest swell builds.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
PZ...None.
&&

$$

UPDATE...RGass
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...DialH
MARINE...DialH

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Prepared by Boulder-Creek.com Weather at: Sun Jan 18 12:30:03 PST 2026