FXUS66 KMTR 180817
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
1217 AM PST Sun Jan 18 2026

...New SHORT TERM, LONG TERM...

.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

&&

.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...
(06Z TAFS)
Issued at 945 PM PST Sat Jan 17 2026

Pesky high clouds are covering up any signs of fog in 
our region, leaving us at the mercy of observations and webcams. 
What we do know, is that tule fog has developed in the Valley once 
again and has snaked into the Delta. Looking at webcams and 
ASOS/AWOS sites, dense fog generally remains confined to this area 
and KCCR as of this posting. Guidance does continue to favor socking 
in the the North Bay later tonight, with KSTS and KAPC bopping 
around MVFR to LIFR conditions. High clouds may play a factor in 
when and for how long IFR to LIFR conditions hold, particularly for 
KAPC and any East Bay terminals. Fog that develops should erode by 
mid to late morning, with VFR conditions returning for the afternoon 
and much of the evening. 

Vicinity of SFO...Quiet and VFR conditions, plus light offshore 
winds continue for much of the TAF cycle. Winds may go variable for 
a bit overnight but return to offshore to northerly by tomorrow 
morning. 

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR conditions continue through the period. 
KSNS should hold with offshore flow through this period, while KMRY 
observes variable to light offshore during the overnight hours. 
Onshore flow returns to KMRY by late morning or early afternoon. 

&&

.MARINE...
(Tonight through next Friday)
Issued at 829 PM PST Sat Jan 17 2026

Gentle to moderate northeast to east breezes persist across the
San Pablo Bay, the Delta, and through the Golden Gate through
early next week while light to gentle northeast to north winds
continue across the rest of the coastal waters. Low seas continue
today, with a northwest swell building to 5 to 6 feet by early to
mid week. This will lead to low to moderate seas.

&&

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

$$

SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...KR
MARINE...KR

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Prepared by Boulder-Creek.com Weather at: Sun Jan 18 00:30:03 PST 2026