FXUS66 KMTR 290532
AFDMTR
Area Forecast Discussion
National Weather Service San Francisco CA
932 PM PST Sun Dec 28 2025
...New AVIATION...
.KEY MESSAGES...
Updated at 128 PM PST Sun Dec 28 2025
- Cold overnight conditions for interior and valley locations
- Rain returns Wednesday and lasts through the weekend
- Coastal flooding from King Tides is expected Wednesday through
Sunday
&&
.UPDATE...
Issued at 854 PM PST Sun Dec 28 2025
No update to the forecast this evening, with colder than normal
temperatures across much of our area. The dry and cool airmass
that has replaced the unsettled weather over the holidays will
persist for the first half of the upcoming week, then another
stretch of potentially impactful rainfall for the second half of
the week into next weekend.
&&
.SHORT TERM...
Issued at 128 PM PST Sun Dec 28 2025
(This evening through Tuesday)
High pressure building into the Intermountain West and a coastal
trough off the West Coast will dominate our weather through Tuesday.
This is a textbook setup for offshore flow. Fortunately, we do not
need to worry about fire weather concerns as we normally would.
Instead, clear and dry conditions will yield cold overnight
conditions. A Cold Weather Advisory has been issued for tonight for
interior and valley locations. This goes for everyone but especially
for those of you who are still without power: do not use generators
or grills inside as carbon monoxide poisoning can result! Whether
you are in the Cold Weather Advisory or not, it is going to be a
cold night and a cold start to the week. Some grief was had over the
minimum temperature forecast due to the aforementioned offshore
flow. Why? Well, offshore flow can bring compressional/downslope
warming. This is why the North Bay Interior Mountains were left out
of the Cold Weather Advisory. 925mb flow (~2500 ft) from the ECMWF
and GFS show 30 knots through there overnight. This will mix down
warmer and drier air aloft which should help keep the area above 36
degrees. There is even a bust scenario where it mixes all the way
down to the North Bay Interior Valleys, but that is not as likely.
Another bust scenario is that the Northern Salinas Valley remains
above 36 degrees with the help of moderate drainage winds.
Nonetheless, the warming and drying trend will continue through
Tuesday with cold overnight conditions.
&&
.LONG TERM...
Issued at 128 PM PST Sun Dec 28 2025
(Wednesday through next Saturday)
Coastal flooding from King Tides returns Wednesday and lasts into
Sunday. This will impact the Monterey Bay Shoreline, San Francisco
Bay Shoreline, San Pablo Bay Shoreline, and the Pacific Coast. If
travel is required, allow extra time as some roads may be closed. Do
not drive around barricades or through water of unknown depth. Take
the necessary actions to protect flood-prone property.
A pattern change is on tap for Wednesday as a surface low pressure
system near the California/Mexico border picks up tropical moisture
on its journey northward. ECMWF and GEFS ensemble IVT forecast shows
their 80 member ensemble mean breaching 250 kg/ms during this time.
It's too soon to say with certainty, but minor flooding in low-
lying, poor drainage, and urban areas as well as flashy
creeks/streams can be expected as early as Wednesday. Tree debris
from this past week that hasn't been disposed of may act to clog
storm drains and gutters, resulting in more flooding. Wind will
increase during this time, but it is not expected to be impactful by
itself. However, the combination of wind and moist soils will
increase the risk for downed trees, especially where trees have
recently been weakened. If you are looking for a sign to put away
your outdoor holiday decorations, this is it. All outdoor
preparations such as securing loose outdoor items, trimming tree
branches, and cleaning out gutters should be finished by Tuesday.
There's also a low chance (<15%) for thunderstorms Wednesday into
Thursday, but that will be heavily dependent on the exact trajectory
of the low. The more impactful of the two systems looks to be Friday
as a surface low pressure system and its attendant cold front come
into Northern California. Both the deterministic ECMWF and GFS
depict a 50+ knot 925mb jet accompanying it which may equate to a
Wind Advisory for portions of the area (mainly looking at the coast
and the higher terrain). The same rain impacts of minor flooding in
low-lying, poor drainage, and urban areas as well as flashy
creeks/streams can be expected during this timeframe. Deterministic
and ensemble river forecasts do not show any mainstem river points
reaching minor flood stage; however, this could be a result of QPF
only recently trending up this morning after the river forecasts
were already completed. HEFS does show a 10% chance of river flow
exceedance for the notoriously flashy spots in Sonoma County of
Russian River at Geyserville (GEYC1), Laguna de Santa Rosa at Stony
Point Road NR Cotati (CTIC1), and Mark West Creek near Mirabel
Heights (MWEC1) which finally dropped below action stage just as I
was typing this.
&&
.AVIATION...
(06Z TAFS)
Issued at 932 PM PST Sun Dec 28 2025
Offshore winds and VFR will continue except tule fog /VLIFR-IFR/
from the Central Valley is forecast to reach into eastern Contra
Costa county late tonight and Monday. Patchy valley fog /VLIFR-
IFR/ also developing due to radiative cooling tonight and Monday
morning.
Vicinity of SFO...VFR. Northeast wind 5 to 10 knots tonight and
Monday becoming northwest near 5 knots Monday afternoon then light
northeast Monday night.
SFO Bridge Approach...Similar to SFO.
Monterey Bay Terminals...VFR. Winds east to southeast 5 to 12 knots
tonight and Monday morning. Winds becoming light and variable to
locally onshore late Monday afternoon then light east to southeast
Monday night.
&&
.MARINE...
(Tonight through next Saturday)
Issued at 854 PM PST Sun Dec 28 2025
A gentle northerly breeze will gradually shift to easterly over
the next 24 hours. Seas will remain moderate through Thursday.
Overall marine conditions will remain favorable before the next
low pressure system brings strong southerly winds and rough seas
by Friday.
&&
.BEACHES...
Issued at 945 AM PST Sun Dec 28 2025
Perigean spring tides (king tides) return Wednesday - Sunday.
This is due to the combination of the full moon on 1/3, lunar
perigee on 1/1, and perihelion on 1/3. In other words all three
planetary bodies are lined up and close to each other. In addition
to the high astronomical tide, the incoming low pressure system
will bring strong onshore winds, generating some storm surge. The
combination of these factors will bring minor coastal flooding to
the low-lying areas near shorelines and tidal waterways during
high tide Wednesday through Sunday. At the San Francisco tidal
gauge, high tide is expected to be 1.5 ft above normal at 7:51 AM
Wednesday, 1.7 ft above normal at 8:41 AM Thursday, 1.8 ft above
normal at 9:34 AM Friday, 1.8 ft above normal at 10:26 AM
Saturday, and 1.6 ft above normal at 11:18 AM Sunday. These
predictions include 0.5 feet of storm surge that will enhance the
astronomical tide and flooding threat. High tide varies up to 90
minutes earlier or later along the Pacific Coast and through the
San Francisco Bay, respectively.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Coastal Flood Advisory from 5 AM Wednesday to 2 PM PST Sunday
for CAZ006-505-506-508-509-529-530.
Cold Weather Advisory from 1 AM to 9 AM PST Monday for CAZ506-
510-513>518-528.
PZ...None.
&&
$$
SHORT TERM...Sarment
LONG TERM....Sarment
AVIATION...Canepa
MARINE...Flynn
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 28 22:30:03 PST 2025
From the National Weather Service
|