FXUS66 KMTR 150228
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
628 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
&&
.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...
(00Z TAFS)
Issued at 512 PM PST Sun Dec 14 2025
Patchy low clouds and fog retreated temporarily before beginning
to fill back in over area terminals. Low cigs and patchy fog,
locally dense in places will prevail through tonight. Models
indicate a late clearing tomorrow morning with cigs anticipated to
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 some terminals.
Vicinity of SFO...VFR conditions prevail currently however low
clouds are anticipated to fill back in tonight with cigs around
800 feet. Cigs expected to persist well into the Monday morning
rush with cigs lifting around 18z.
SFO Bridge Approach...same as SFO.
Monterey Bay Terminals...IFR cigs will prevail through tonight
with clearing anticipated after 17z Monday morning.
&&
.MARINE...
(Today through Friday)
Issued at 204 PM PST Sun Dec 14 2025
Southerly flow will prevail north of Pigeon Point and northerly
flow will prevail south of Pigeon Point. Winds will be gentle to
moderate, but locally moderate to fresh south of Point Sur through
Monday as the first in a series of weak systems reaches the
coastal waters. Rain chances increase this week. Low seas persist
through the remainder of the weekend before building to moderate
to rough by mid week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...None.
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...MM
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Prepared by Boulder-Creek.com Weather at: Sun Dec 14 20:30:02 PST 2025
From the National Weather Service
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