textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 117 AM PST Mon Dec 8 2025

- Another round of fog this morning in the valleys across the Bay Area.

- Fairly consistent weather pattern continues this week.

- Next chance of rain around the 15th.

SHORT TERM

Issued at 117 AM PST Mon Dec 8 2025 (Today and tonight)

Tule Fog remains in the Central Valley and there is slightly more low stratus coverage across the Bay Area than this time last night. There is a good chance for these clouds to expand down to the surface as the the wind continues to calm through the morning. The most likely locations to develop fog are the North Bay Valleys, Interior East Bay Valleys, and the Santa Clara Valley. There's more uncertainty along the Bay side of San Mateo County. Typically this area is less prone to fog than the cooler valleys, but is the best set-up for it. Light NNE winds over the Bay don't suffer from the downslope drying of winds with a westerly component. For example, historically the visibility at SFO drops below 3 miles 8% of the time in December between 5AM and 10AM. If we add a NNE wind direction constraint to these variables, the probability increases to 17%. On the other hand, NW winds bring this low visibility only 4% of the time. The otherwise clear skies and long December nights also help with the radiative cooling to generate this fog, and cloud top radiation helps to sustain it. The complicating factor is the relatively warm water in the Bay (55F) compared to the air temp (45F). This induces some instability that will work to lift fog into a low cloud deck if the low level winds don't calm this morning. In the end, I'll give a 30% chance for fog in Eastern San Mateo, 50% for the Santa Clara Valley, and 80% across the North and East Bay Valleys. Otherwise the weather will be quite similar to the last couple days as the fog and low clouds gradually clear through the day and temperatures under the morning stratus struggle to get into the 60s in the afternoon.

LONG TERM

Issued at 117 AM PST Mon Dec 8 2025 (Tuesday through Sunday)

The long term forecast is mostly boring. There is a hint of rain at the end of the 7-day window, but let's spend a minute discussing this dry spell first. If you've read any of our AFDs in the last week, you know it's caused by a "ridiculously resilient ridge" over California that is keeping the storm track well to our North. It's now been 17 days since San Francisco recorded any rain, and that streak will very likely extend into the mid 20s. How unusual is that? Well it turns out a long dry spell in the middle of the rainy season is actually pretty common. There have been 54 instances of a dry spell lasting 24 days or more between November and March since 1849. In other words, there is a 31% (54/176) chance of getting a dry spell at least this long any given Winter. The longest such streak was 60 days from November 17, 1876 to January 15, 1877. We're not expected to get anywhere near that record as it looks like a pattern change is finally on the horizon. More and more ensemble members are agreeing that the ridge will finally break down with more a more active zonal pattern bringing the jet stream and chances for rain back to the Bay Area. 40/50 ECMWF ensemble members bring some rain to the Bay Area next week, with an outside chance for heavier rain the following weekend. We'll wait and see for now, but our official forecast finally has a decent probability of precipitation starting on the 15th.

AVIATION

(06Z TAFS) Issued at 948 PM PST Sun Dec 7 2025

Low clouds and fog are building in the North Bay and interior East Bay, but have cleared over STS and LVK while APC remains IFR. Expect cloud cover to lower further into the night while the fog to becomes thicker. The OAK and SJC see CIGs arrive overnight with some reductions in visibilities. Winds stay mostly light to moderate through the morning, with wind directions determined by more localized affects. Cloud cover and fog will be slow to erode into Monday, but conditions look to improve into the afternoon. However, the North and East Bay will continue to struggle with low clouds and fog, causing some doubt for clearing at STS and LVK, while APC doesn't clear. As cloud cover erodes, pockets of haze will affect much of the region. CIGs and fog reform for STS and APC into the evening.

Vicinity of SFO...VFR through the TAF period. Winds become lighter into the night with scattered low clouds building into the area, along with some slight reduction in visibilities. Cloud cover thins into the afternoon and winds become slightly more moderate and northwesterly.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the TAF period. Winds stay light for MRY through the TAF period, while SNS sees moderate northwest winds become light into the night. North to northwest winds return Monday afternoon with the potential for haze.

MARINE

(Tonight through next Saturday) Issued at 948 PM PST Sun Dec 7 2025

Moderate to fresh north to northwest winds continue for the southern waters. Moderate seas with wave heights 6 to 8 feet across the outer waters will subside to around 4 to 6 feet for Monday. Winds and swell increase Monday night, with strong gusts possible across the waters. A new, long period northwesterly swell is anticipated by Wednesday and looks to exit late Friday.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 9 AM PST Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory from 3 PM this afternoon to 3 AM PST Tuesday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory from 3 PM this afternoon to 9 AM PST Tuesday for Pigeon Pt to Pt Pinos 10-60 NM.