textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1215 PM PST Fri Dec 5 2025

- Persistent forecast through the next seven days with benign conditions and no precipitation expected

- Impacts from Tule Fog in the North Bay and interior East Bay valleys

- Next chance for rain towards the middle of the month

UPDATE

Issued at 924 PM PST Fri Dec 5 2025

Updated the overnight low temperatures and issued a Cold Weather Advisory for most of the North Bay. Temperatures across the North Bay are generally running a few degrees cooler than at this time last night with Petaluma dropping to 37 around 8pm. The Tule Fog has struggled making progress westward into our area so far tonight. Also, a subtle return of the marine layer is helping to produce stratus along northwest facing areas of the coast from Bodega Bay south to Pescadero. Otherwise, the forecast remains on track for the remainder of the Bay Area and Central Coast.

SHORT TERM

Issued at 1259 PM PST Fri Dec 5 2025 (This evening through Saturday)

Owing to the slower than expected stratus mix out and warming in the valleys of the North Bay and interior East Bay, have opted to decrease today's highs and tonight's lows in both areas, with the high temperatures now expected to rest in the middle to upper 50s and lows in the upper 30s to lower 40s in the area, with areas in the eastern tier of Contra Costa County going up to the lower 50s today.

For all other regions, the previous discussion is still valid: Satellite imagery reveals lingering impacts from the Tule Fog spillover across the valleys of the North Bay and the interior East Bay. The mix out process continues to be rather slow with marginal shrinkage of the stratus deck in the late morning, with the bulk of the mixing out expected to occur this afternoon into the evening. There is also a potential for drizzle to develop in the coastal waters tonight, fringe effects of a storm system that is bringing rain to the Pacific Northwest but is not expected to bring any precipitation on the land side of the Bay Area and Central Coast. This, in turn, could support the return of coastal stratus to the region. Otherwise, the weather remains generally clear through the day, as upper level ridging dominates the western United States. High temperatures today and Saturday range from the lower to middle 60s across the inland valleys, with the southern Salinas Valley reaching the upper 60s to near 70, and the upper 50s and the lower 60s near the coast. Lows will generally range from the lower to middle 40s inland and the middle to upper 40s along the coast. Some locations in southern Monterey County will drop into the middle 30s. Will need to monitor the need for a Cold Weather Advisory if the temperatures drop due to enhanced radiational cooling, or if temperatures in the North and East Bays stay cool due to lingering stratus impacts reducing the daytime heating effects.

LONG TERM

Issued at 1215 PM PST Fri Dec 5 2025 (Saturday night through next Thursday)

Ridging will dominate the weather patterns through the rest of the 7- day outlook, enabling a gradual warming trend across the region. Rather than a day when the temperatures shoot upwards, we will experience a extended crescendo where the highs shoot up by a degree or two each day until you notice that by the middle of next week, temperatures are running 5 to 10 degrees above seasonal averages and highs in the inland valleys have reached the upper 60s to middle 70s. By the end of the 7-day forecast period, there are hints that a burst of offshore flow could come to the region, although exactly how strong that flow will be is open to lots of refinement.

Longer range model guidance suggests a possible change in the weather pattern towards the middle of the month. Ensemble model cluster analysis depicts the majority of model runs showing a continuing ridge, but substantial minorities (somewhere around 30- 40% of the ensemble members) depict a breakdown of the ridge. CPC guidance continues to show a slight lean, emphasize, a slight lean, towards precipitation totals above seasonal averages for December 13- 19 across the Bay Area. For context, within the long-term climatic averages, downtown San Francisco receives a little over an inch of rain during this period.

AVIATION

(06Z TAFS) Issued at 953 PM PST Fri Dec 5 2025

An odd mixture of stratus along the coast and IFR/Tule fog moving into eastern portions of the CWA. Leaned on HREF guidance to capture stratus moving in along the coast with moderate confidence that stratus/MVFR conditions will persist through much of the overnight period. For areas impacted by stratus, not anticipating visibilities to drop much. For areas impacted by Tule Fog, visibilities will be around 1-2SM with the potential for dense fog (1/4SM) to develop in the North Bay. APC is likely to see some impact from Tule Fog tonight but confidence is lower as to how long fog will be over the airport. Followed persistence forecast for the timing of when conditions will improve tomorrow (generally looking at late morning/early afternoon clearing). Moderate onshore winds redevelop tomorrow afternoon/evening before weakening and becoming variable to lightly offshore overnight.

Vicinity of SFO...MVFR through much of the overnight period. Models did not have a good grasp on the reemerging marine layer and accompanying marine stratus tonight with only HREF guidance showing the stratus that is currently over SFO. HREF guidance keeps low clouds in the vicinity of SFO through the rest of tonight so opted to utilize the HREF timing. Not anticipating fog to develop at SFO with CIGs expected to predominantly be on the MVFR-IFR border overnight. Winds remain light and slightly offshore overnight before more moderate onshore winds return during the day tomorrow.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. HREF guidance is best depicting the current marine stratus setup with stratus to stay offshore tonight. There is some potential for low clouds to reach MRY after 12Z but no major impacts are expected at the airport. Winds remain light overnight before more moderate onshore winds return during the afternoon.

MARINE

(Tonight through next Thursday) Issued at 924 PM PST Fri Dec 5 2025

Northwesterly winds have increased to fresh to strong offshore with localized near gale force gusts possible across the outer waters. Winds remain elevated through the weekend and into next week but there may be brief periods where winds weaken across the coastal waters. Moderate seas with wave heights between 6 to 8 feet continue through the weekend. Moderate, long-period northwesterly swell returns by mid next week with wave heights to build.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory until 3 PM PST Sunday for CAZ006-506-508- 529-530.

Cold Weather Advisory until 8 AM PST Saturday for CAZ502-504-506.

PZ...Small Craft Advisory until 3 AM PST Saturday for Pt Arena to Pt Reyes 0-10 nm.

Small Craft Advisory from 9 AM Saturday to 3 AM PST Sunday for Pt Pinos to Pt Piedras Blancas 0-10 nm.

Small Craft Advisory until 9 AM PST Saturday for Pt Arena to Pt Reyes 10-60 NM.

Small Craft Advisory until 9 AM PST Sunday for Pigeon Pt to Pt Pinos 10-60 NM.