626
FXUS66 KMTR 100513
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco CA
913 PM PST Tue Dec 9 2025

...New UPDATE...

.KEY MESSAGES...
Updated at 1256 PM PST Tue Dec 9 2025

 - Tule fog and stratus return tonight for Bay Area valleys.

 - Quiet weather continues, with high temperatures increasing
   through Friday.

 - Light rain remains possible early next week.

&&

.UPDATE...
Issued at 913 PM PST Tue Dec 9 2025

Temperatures across the region are running warmer than they were 24
hours ago across the higher elevations and cooler to about the same
across the lower elevations. What`s the difference between those
areas? Fog! Satellite imagery shows a fairly expansive area of fog
across the North Bay and East Bay valleys tonight. Sites in Byron,
Livermore, and Napa are reporting lowered visibilities around 2-3SM
with ceilings around 300 to 500 ft. High resolution model guidance
suggests localized dense fog is possible within the delta and San
Pablo/Suisun Bay and extending up into the North Bay and East Bay
Valleys. If you encounter fog while driving, remember to slow down
and prepare for unexpected changes in visibility. For the interior
Central Coast, the lack of fog/cloud cover will lead to increased
radiational cooling and see temperatures drop into the mid to upper
30s. There may be pockets of low 30s to upper 20s across the higher
elevations in that area. If you reside in that area, make sure to
bundle up during your morning commute.&&

.SHORT TERM...
Issued at 1256 PM PST Tue Dec 9 2025
(This evening through Wednesday)

Another day of watching the stratus slowly erode across the Bay
area. The North Bay Valleys seem to be on track to erode by mid to
late afternoon, which should keep high temperatures fairly chilly up
there. It`s been fun, yet challenging and humbling experience to try
and nail the stratus erosion timing and high temperature forecast.
This will continue to be the trend into Wednesday, though hopefully
we get a little more compression from the high pressure system and
perhaps slightly stronger offshore flow. If that happens, we could
see warmer temperatures than forecast; however, I trended with a
slightly more pessimistic forecast for Wednesday. If your`e outside
the East and North Bay areas, warmer weather is on tap for
Wednesday.

The area area to watch will be interior Central Coast temperatures
tonight. Ended up tweaking the values in these area based on the
past few nights being a touch colder than expected.

&&

.LONG TERM...
Issued at 1256 PM PST Tue Dec 9 2025
(Wednesday night through next Monday)

Heights will build into for the later portion of the work week,
leading to high temperatures climbing a few degrees each day. The
question will be, what does that mean for our friends who have been
stuck with stratus? The ridge should limit the spread of the stratus
and fog, due to the marine layer compressing. If any clouds and fog
do form, they should at least erode faster leading to smaller
warming trend for these areas. High temperatures falter a few
degrees as we head towards the weekend as upper level ridging slides
eastwards. The next chance for rain may occur early next week. The
dates of when this occurs seem to continue to be pushed back, so
stay tuned.

&&

.AVIATION...
(00Z TAFS)
Issued at 602 PST Tue Dec 9 2025

Additional warming occurred today in the lower levels of the
atmosphere per recent Oakland upper air sounding data and Bodega
Bay profiler data. This strengthened the lower level temperature
inversion today, however the difference between ground level and
the base of the temperature inversion did not change much at both
of these locations, at least not yet. The SAC-SFO pressure gradient
is 1.7 mb and the WMC-SFO 0.9 mb. The WMC-SFO gradient is forecast
to strengthen tonight and Wednesday, both gradients support ongoing
offshore winds tonight and Wednesday.

The synoptic pattern remains favorable for plentiful tule fog and
low stratus to continue over the Central Valley, corresponding to
ongoing chilly temperatures and higher surface pressures in the
valley. There`ll be very little if any interference in outgoing
radiative cooling tonight; it`s dry above the lower level temperature
inversion and cirrus clouds will be at a minimum tonight. Expect
redevelopment of fog and stratus /LIFR-IFR/ in our area including
the potential for dense tule fog /VLIFR/ to be transported into the
Bay Area on light offshore winds tonight and Wednesday. Key to mix
out times, if they are earlier tomorrow than recently observed,
will be the base of the lower level temperature inversion, if it
does not move downward much then it`s a persistence forecast with
late day break out times if at all. In areas where VFR has prevailed
recently the probability of VFR or mixing out from late night and
morning fog and stratus /VFLIFR-IFR/ is greater for Wednesday.
This is a very challenging forecast, forecast confidence regarding
mix out times Wednesday is low.

Vicinity of SFO...Low confidence VFR forecast tonight, with ongoing
light offshore surface winds these winds may transport stratus
ceilings and fog to SFO tonight and Wednesday morning. The difference
between the air temperature and dew point temperature is small,
radiative cooling and advection may work together to bring the
atmosphere back to saturation i.e. stratus and fog development.
Offshore winds continue for the 00z TAF.

SFO Bridge Approach...Slant range visibility may be moderate to
poor at sunrise and sunset due to trapped hazy conditions. Light
offshore winds may also bring low stratus and fog to the SFO
approach, bringing a cloud ceiling and reducing the visibility
anyhow. It`s a low confidence VFR forecast for SFO and the SFO
approach.

Monterey Bay Terminals...The highest probability of VFR is here,
though radiative cooling may result in patchy fog to patchy dense
fog /LIFR-VLIFR/ in the Salinas Valley tonight and Wednesday
morning. Cold air drainage winds will result in southeasterly
winds tonight and Wednesday, possibly shifting to light and
variable temporarily Wednesday afternoon.

&&

.MARINE...
(Tonight through next Monday)
Issued at 408 PM PST Tue Dec 9 2025

Northerly flow remains over the waters with high pressure off the
coast. Winds are locally stronger south of Point Pinos leading to
hazardous conditions today. Winds will strengthen across all
outer waters by midweek. A new, long period northwesterly swell
is expected by midday Wednesday, lasting into the early weekend.

&&

.BEACHES...
Issued at 132 AM PST Tue Dec 9 2025

Long period swell will impact the coast Wednesday - Friday. This
energy brings strong rip currents, an increased risk for sneaker
waves, and large breaking waves. NW swell around 8 feet with a 15
second period will translate to breaking waves up to 15-20 feet.
These conditions may warrant a Beach Hazards Statement, particularly
with the warm weather likely luring more people to the Beach.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
CA...Beach Hazards Statement from 7 AM PST Wednesday through Friday
     evening for CAZ006-505-509-529-530.

PZ...Small Craft Advisory until 9 AM PST Wednesday for Pt Pinos to Pt
     Piedras Blancas 0-10 nm.

     Small Craft Advisory until 3 AM PST Thursday for Pt Arena to Pt
     Reyes 10-60 NM.

     Small Craft Advisory until 3 PM PST Wednesday for Pigeon Pt to
     Pt Pinos 10-60 NM.

&&

$$

SHORT TERM...KR
LONG TERM....KR
AVIATION...Canepa
MARINE...MM

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