FXUS66 KMTR 100545
AFDMTR

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

...New AVIATION, MARINE...

.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. 

&&

.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...
(06Z TAFS)
Issued at 944 PM PST Tue Dec 9 2025

Additional warming in the lower levels of the atmosphere per 
recent Oakland upper air sounding data and Bodega Bay profiler 
data, strengthened the lower level temperature inversion today. 
However, the difference between ground level and the base of the 
temperature inversion so far has not changed much since early
evening, at least not yet. The SAC-SFO pressure gradient is 1.5 
mb and the WMC-SFO 1.6 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...VFR initially forecast tonight, then low to
moderate confidence IFR tempo stratus ceiling develops 08z-12z 
then IFR prevailing to 18z Wednesday. The combination of radiative
cooling and light offshore surface winds increases the probability
of stratus /IFR/. Will need to closely monitor satellite and surface
observations for potential fog development as well. Offshore winds
are forecast to prevail during the 06z TAF.

SFO Bridge Approach...Slant range visibility moderate to poor at 
sunrise and sunset due to trapped hazy conditions. Light offshore 
winds may end up bringing low stratus and fog to the SFO approach 
later tonight and Wednesday morning.

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. Cold air drainage winds
redevelop Wednesday night and Thursday morning. 

&&

.MARINE...
(Tonight through next Monday)
Issued at 929 PM PST Tue Dec 9 2025

High pressure will result in northerly winds over the coastal
waters. High pressure will also build over the Great Basin tonight
and Wednesday resulting in additional offshore winds across the
Delta to the San Francisco Bay. Winds will strengthen across all
outer waters by midweek. A new, long period northwesterly swell is
expected Wednesday, lasting into the early weekend.

&&

.BEACHES...
Issued at 932 PM 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...Canepa

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Prepared by Boulder-Creek.com Weather at: Tue Dec 9 22:30:02 PST 2025