FXUS66 KMTR 140850
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
1250 AM PST Sun Dec 14 2025
...New SHORT TERM, LONG TERM...
.KEY MESSAGES...
Updated at 1202 AM PST Sun Dec 14 2025
- Dense fog this morning across the North Bay valleys and East
Bay interior valleys.
- Beneficial rain expected this week.
- Heavier rain and strong wind possible next week.
&&
.SHORT TERM...
Issued at 1202 AM PST Sun Dec 14 2025
(Today and tonight)
We are now on the backside of the 500 mb ridge that dominated the
weather for the last couple weeks. A short wave trough is further
weakening the long wave ridging. This feature brought a strong
southerly surge of stratus on Saturday, but wasn't enough to mix
out the radiation fog across the valleys. So now we have both
coastal stratus and inland valley fog. Boundary layer averaged winds
have shifted from easterly to southerly over the last 24 hours,
but remain weak at the surface. Dense fog is being reported across
the North Bay valleys and interior East Bay valleys. This fog will
persist through late morning before clearing, and a Dense Fog
Advisory is in effect until 11 AM. Afternoon temperatures will be
cooler than they have been with more cloud coverage and dropping
850 mb temps. Both the long wave ridge and short wave trough will
continue to slide East through the day. There is another good
chance for fog impacts Sunday night as the lower atmosphere
remains poorly mixed.
&&
.LONG TERM...
Issued at 1202 AM PST Sun Dec 14 2025
(Monday through Saturday)
500 mb zonal flow with a tighter pressure gradient will move in by
Tuesday and persist through the week. As this new pattern lines up
with higher moisture it will support a few rounds of light rain.
Without a deep trough there is no real threat of heavy rain this
week. High clouds on Monday will warn of the approaching rain,
with the first round expected Tuesday through Wednesday. The
current forecast has been pretty consistent with around 1/4" in
the North Bay and less than 1/10" everywhere else. While the zonal
flow will persist, drier air will move in Thursday likely
bringing a break in the rain. The next round will move in Friday
and persist through the weekend. Beyond next weekend there is a
lot of uncertainty in the details, but the ensemble cluster
analysis reveals good agreement in the overall pattern evolving to
feature deep troughing just off the coast. This could support an
atmospheric river early next week if the moisture plume lines up
right. The Climate Prediction Center continues to show a moderate
risk for both strong winds and heavy rain from 12/20-12/26.
&&
.AVIATION...
(06Z TAFS)
Issued at 950 PM PST Sat Dec 13 2025
Stratus is spreading into coastal airports (HAF, MRY, SNS, SFO)
while fog is impacting several interior airports (STS, APC). Pushed
back the arrival of fog to LVK to 09Z but otherwise fog/stratus
arrived early to on time this evening. Current thinking is that
sites experiencing stratus will see MVFR-IFR conditions while
interior sites that are expected to see fog will, at least
temporarily, see IFR to LIFR conditions. Continued a persistence
forecast of clearing between 19-20Z with some sites potentially
clearing closer to 21Z. Guidance backed off of favoring clearing
around 18Z and is now more in line with persistence clearing times.
Fog and stratus are likely to return again tomorrow night given the
current weather set up. Winds remain light and variable but become
more moderate and onshore during the afternoon/evening hours.
Vicinity of SFO...MVFR with some potential for IFR overnight. MVFR
CIGs have reached SFO and are starting to fill in across the SF Bay.
Low to moderate confidence that IFR CIGs will at least temporarily
develop overnight. Winds stay light and variable for much of the
night before strengthening slightly and shifting onshore again
during the day.
SFO Bridge Approach...Stratus filtering in across the SF Bay will
result in a loss of VAPS on the SFO Bridge approach. This is likely
to persist through 19-20Z (similar to SFO) but some guidance does
indicate it could take longer for stratus over the bay to clear than
over land.
Monterey Bay Terminals...IFR-MVFR. CIGs are on the border of IFR
(MRY) and MVFR (SNS) with both airports to drop to the IFR-LIFR
border later tonight. Visibilities are currently forecast to
decrease to 3-4SM but GFSLAMP guidance shows some potential for
1/4SM visibilities and fog to develop at MRY between 12-16Z. Leaned
towards clearing around 20Z for both sites but it could occur
slightly earlier around 19Z. Winds stay light through much of the
forecast period with a weak sea breeze developing during the
afternoon/evening hours.
&&
.MARINE...
(Tonight through next Friday)
Issued at 903 PM PST Sat Dec 13 2025
A gentle to moderate breeze continues across the coastal waters
through this weekend. Winds increase to moderate to fresh across
the southern coastal waters Monday as the first in a series of
weak systems reaches the coastal waters. Rain chances increase
early to midweek with light rain possible for much of next week.
Low seas persist through the remainder of the weekend before
building to moderate to rough by mid next week.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Dense Fog Advisory until 11 AM PST this morning for CAZ506-510.
PZ...Small Craft Advisory from 3 PM to 9 PM PST Monday for Pt Pinos
to Pt Piedras Blancas 0-10 nm.
&&
$$
SHORT TERM...Flynn
LONG TERM....Flynn
AVIATION...Kennedy
MARINE...Kennedy
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
Prepared by Boulder-Creek.com Weather at: Sun Dec 14 02:30:02 PST 2025
From the National Weather Service
|