688
FXUS66 KMTR 140033
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
433 PM PST Sat Dec 13 2025

...New AVIATION, MARINE...

.KEY MESSAGES...
Updated at 1216 PM PST Sat Dec 13 2025

 - Stratus persists over the North and East Bay valleys and the
   coastal regions

 - Wetter conditions return for the upcoming work week

&&

.SHORT TERM...
Issued at 1216 PM PST Sat Dec 13 2025
(This evening through Sunday)

The upper level ridge that brought us the days of stable weather is
beginning to move off to the east, and an shortwave trough has set
up across the State. Satellite imagery reveals that stratus
persists across the valleys over the North Bay and interior East
Bay valleys in addition to the southeastern part of San Mateo
County, outgrowths of the Tule Fog across the Central Valley, and
the immediate coastal regions near Point Reyes, San Mateo County,
and south of Point Sur, as a southerly surge takes hold just off
the coast. There is low to very low confidence in any clearing
across the coastal regions, the Sonoma County valleys, the 101
corridor of Marin County, and the northern and eastern parts of
Contra Costa County. Everywhere else, some clearing is possible
through the rest of the afternoon.

High temperatures will be broadly similar to those yesterday. The
coldest regions will be the eastern part of Marin County and the
northern and eastern regions of Contra Costa County, where highs
will remain in the middle to upper 40s. At the other extreme, the
interior Central Coast valleys, shielded from both the coastal
stratus and the Tule Fog, reach the middle to upper 70s. In general,
the Bay Area valleys see highs in the middle 50s to lower 60s,
although lingering stratus in the Sonoma County valleys makes the
high temperatures a little uncertain, with the potential for the
region to remain in the 40s if the stratus persists all day.

On Sunday, the shortwave trough crawls across the state and ridging
redevelops on its backside, with conditions expected to be broadly
similar to today`s.

&&

.LONG TERM...
Issued at 1216 PM PST Sat Dec 13 2025
(Sunday night through next Friday)

As we head into the early part of upcoming work week, the ridge will
continue to flatten, a pattern change that brings more zonal flow to
the region by Tuesday. This new pattern should help scour out the
Tule Fog and, when combined with a plume of moisture with PWAT
values up to 1.25 inches, brings a chance of light rain to the
region Tuesday and Wednesday, with rainfall totals focused on the
North Bay. A weak ridge will move through the state on Thursday and
Friday, but the overall flow should remain generally zonal and
lingering showers and drizzle are possible from remnant moisture in
the region.

Towards and beyond the end of the 7-day outlook, the forecast points
towards another round of wet weather across the region for the
weekend of the 20th and 21st as a deep trough in the eastern Pacific
coincides with another plume of moisture moving through the West
Coast. With a system this far out, details are still very much in
flux. The CPC maintains a strong lean (60-80% probability) towards
rainfall totals above the seasonal average in the 6-10 day window
(December 19-23). Beyond that, the CPC maintains a moderate risk (40-
60% probability) of heavy rainfall and high winds into the Christmas
holiday period with a 60-70% probability of rainfall totals above
the seasonal average through the 8-14 day period (December 21-27),
which would impact any holiday travel plans.

&&

.AVIATION...
(00Z TAFS)
Issued at 432 PM PST Sat Dec 13 2025

Mix of VFR and MVFR thanks to Tule Fog approaching from the east and
marine stratus from the west. Winds are generally light across the
board with locally breezier conditions along the coastline. Highest
confidence in MVFR CIGs but in areas impacted by fog (STS, APC, LVK,
SJC ) IFR-LIFR CIGs and visibilities down to 1/4SM are possible.
Confidence is lower that visibilities will lower below 4-5SM in
areas that are impacted by marine stratus (likely OAK, SFO, MRY,
SNS, and HAF). Generally followed persistence timing for when CIGs
will clear tomorrow (generally around 19-20Z) with model guidance
indicating potential for clearing closer to 18-19Z. Fog and stratus
are likely to return again tomorrow night.

Vicinity of SFO...VFR becoming MVFR overnight. Confidence is
moderate that any CIGs that reach SFO tonight will be MVFR with
guidance indicating at least some potential for IFR CIGs to
temporarily develop. LAMP guidance shows around a 20% chance chance
of LIFR conditions developing between 13-17Z. Clearing is expected
by 19Z with VFR through the remainder of the TAF period. Winds stay
light and variable to offshore through tomorrow afternoon when a
moderate sea breeze looks to develop.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...Stratus is right on the edge of the
Monterey Peninsula with stratus intermittently impacting MRY this
afternoon. Kept MVFR conditions as the prevailing for MRY through
later this evening with stratus arriving at SNS by 02-03Z. CIGs
lower to IFR-LIFR overnight with some potential for visibilities to
drop down to 1/4SM early tomorrow morning. Confidence was low that
visibilities would decrease that low at MRY and SNS so only pushed
visibilities down to 4SM with the 00Z TAF update. LAMP guidance
suggests visibilities will fluctuate throughout the night so a tempo
may be needed to address visibility decreases.

&&

.MARINE...
(Tonight through next Friday)
Issued at 432 PM PST Sat Dec 13 2025

A weak surface low pressure circulation over the outer coastal
waters will result in gentle to moderate southerly breezes. Winds
will veer to become northwesterly tomorrow night. Seas will remain
moderate through Monday, building to become rough in the outer
waters and northern inner waters by Tuesday. Several disturbances
passing to the north next week will bring renewed rain chances and
wind shifts.

&&

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

$$

SHORT TERM...DialH
LONG TERM....DialH
AVIATION...Kennedy
MARINE...Canepa

Visit us at www.weather.gov/sanfrancisco

Follow us on Facebook, X, and YouTube at:
www.facebook.com/nwsbayarea
x.com/nwsbayarea
www.youtube.com/nwsbayarea