FXUS66 KMTR 150536
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
936 PM PST Sun Dec 14 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 122 PM PST Sun Dec 14 2025
- Stratus persists over the North and East Bay valleys and the
coastal regions
- Generally beneficial rain beginning this week
- Heavier rain and strong wind possible next week
&&
.UPDATE...
Issued at 911 PM PST Sun Dec 14 2025
Fog set in a bit earlier this evening and in particular for the
valleys of Sonoma County. As a result, and perhaps you've already
guessed this, another Dense Fog Advisory has been issued for the
North Bay and East Bay valleys. This will run until 11AM on
Monday, which means foggy conditions can be expected for the
morning commute. We will need to keep an eye on visibilities for
the Santa Clara Valley as well as San Jose and Hollister have
already started to drop. For those commuting Monday morning, be
sure to check the forecast and current weather and traffic
conditions before heading out and allow extra time for your
commute. If driving, slow down, use your headlights (not your high
beams), and leave plenty of distance ahead of you.
&&
.SHORT TERM...
Issued at 122 PM PST Sun Dec 14 2025
(This evening through Monday)
The interaction between Tule Fog outgrowth from the east, and
coastal stratus development from the west, continues to feature as
the main short-term forecast issue as a shortwave trough passes over
the state. The Salinas Valley has mostly cleared out, and the
Monterey-Salinas region has generally cleared out, with lingering
coastal stratus observed near Pacific Grove and the immediate coast
between Point Lobos and Point Sur. The coastal plain of Santa Cruz
County and the San Juan Bautista-Hollister valley region remain
socked in, the former extending up the coast of San Mateo County,
and the latter connected to the extensive inland stratus that
persists across much of the Bay Area valleys. If you look closely at
the satellite loop you could make out patches of clearing on the
fringes -- the Cloverdale area in extreme northern Sonoma County,
Lake Berryessa in northeastern Napa County, parts of Livermore,
western sections of Alameda County, and the southwest corner of San
Francisco. Overall, there is much more stratus coverage today than
we saw this time yesterday. As a result, confidence in the clearing
of the North Bay valleys, the northern and eastern sections of
Contra Costa County, and even southeastern San Mateo Peninsula and
the Santa Clara Valley has decreased. For the moment, the high
temperatures today are similar to those from the overnight forecast
update, with highs in the lower to middle 50s in the Bay Area
valleys, into the middle to upper 40s in eastern Marin County and
northern and eastern Contra Costa County, the upper 50s to lower 60s
along the Pacific coast, and the middle 60s to the lower 70s in the
Salinas Valley. There's a chance that the temperatures could still
undershoot the official forecast this afternoon, which comes into
play if the clearing out process continues to lag the model
projections.
On Monday, conditions are expected to be broadly similar to today's
with a similar evolution of the stratus deck, as ridging forms on
the backside of the shortwave trough. This ridge is remarkably
positively tilted, such that the flow pattern off the California
coast is quite zonal. This is a clue to the forthcoming pattern
change, and so are the high clouds that are expected to flow over
the region, thus increasing the uncertainty over the forecast. Will
the high clouds bring breezier flow aloft that could help us scour
out the Tule Fog, or will they inhibit solar heating on Monday
afternoon and keep the stratus around through the day? For now, have
leaned towards another day of slower clearing, and have tamped
Monday's lows cooler than the deterministic NBM output gives.
&&
.LONG TERM...
Issued at 122 PM PST Sun Dec 14 2025
(Monday night through next Saturday)
More zonal flow will come to the region on Tuesday, allowing a
pattern change which will gradually open the proverbial storm door
and lead to wetter conditions through the balance of the 7-day
outlook and beyond. The first of the systems will come through
Tuesday into Wednesday, with generally beneficial rainfall across
our region focused on the North Bay, where rain totals will lie
around 0.5-0.75" for the Sonoma coastal ranges, the 0.3-0.5" for the
Mayacamas, and 0.1-0.25" for the valleys. South of the Golden Gate,
rainfall totals remain generally less than 0.1", with a few
hundredths of an inch being the absolute maximum total across the
Central Coast. More substantial rain is expected late on Thursday
into Friday and the upcoming weekend, with the current forecast
showing two distinct pulses of rain, one on Thursday and Friday and
another for the upcoming weekend, each with the potential for more
significant rainfall totals than the forecast for the Tuesday-
Wednesday system. Initial forecasts suggest that rain totals over
one inch are possible for the North Bay mountains. Beyond the
upcoming weekend, uncertainty becomes high to very high, but
ensemble model cluster analysis suggests good agreement in a deep
upper level trough setting up in the eastern Pacific, which could
support an atmospheric river setup assuming that the moisture plume
sets up in the right place. The latest CPC outlooks suggest that the
North Bay faces a high risk (over 60% probability) of heavy rain
early next week, with the rest of the region seeing a moderate risk
(40-60% probability) of heavy rain in addition to the entire Bay
Area and the northern Central Coast seeing a moderate risk of strong
winds in the 8-14 day period (December 22-28).
&&
.AVIATION...
(06Z TAFS)
Issued at 925 PM PST Sun Dec 14 2025
Patchy low clouds and fog are beginning to fill back in over the
region. Low cigs and locally dense fog is expected once again
tonight. Models indicate cigs will scatter out around 17z-19z.
However high clouds drifting in over the region may help mix out
the boundary layer a bit resulting in some earlier clearing Monday
morning across area terminals.
Vicinity of SFO...VFR conditions prevail currently however areas
of patchy low clouds are anticipated to fill back in over the bay
tonight. Confidence is low as to the extent of coverage impacting
SFO and OAK. Models indicate cigs may stay out of SFO and OAK
however satellite imagery indicates rapid spread close to
the terminals and will need to watch closely.
SFO Bridge Approach...Low clouds over the approach expected to
fill in overnight with locally dense fog.
Monterey Bay Terminals...IFR cigs will prevail through tonight
with clearing anticipated after 17z Monday morning.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 911 PM PST Sun Dec 14 2025
Southerly flow will prevail north of Pigeon Point ahead of an
approaching frontal system. Light to moderate northwesterly flow
will prevail across much of the coastal waters with the exception
of areas north of Pigeon Point that will turn increasing to the
south ahead of an approaching frontal system. Slightly stronger
winds are expected along the immediate coast south of Point Sur
through Monday as the first in a series of weak systems reaches
the coastal waters. Rain chances increase this week. Light seas
will gradually build becoming moderate to rough by mid week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory until 11 AM PST Monday for CAZ506-510.
PZ...Small Craft Advisory from 3 PM Monday to 9 AM PST Tuesday for Pt
Pinos to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...DialH
LONG TERM....DialH
AVIATION...CW
MARINE...CW
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Prepared by Boulder-Creek.com Weather at: Mon Dec 15 00:30:07 PST 2025
From the National Weather Service
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