textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1159 AM PDT Wed Sep 2 2026

- Well below normal temperatures with beneficial, light rain chances through Thursday

- Gradual warming and drying trend with the return of the marine layer Friday into the weekend

SHORT TERM

Issued at 1159 AM PDT Wed Sep 2 2026 (This afternoon through Thursday)

KMUX shows a band of light precipitation bisecting the Bay Area and moving east. Still waiting on a bucket tip south of the Golden Gate Bridge; nonetheless, it won't amount to much as the band continues to weaken. This pre-frontal rain has overperformed the official forecast with Mt. Tam measuring 0.57" in the last 24 hours. The overperformance is likely due to the struggles of guidance/models in the shoulder seasons. The cold frontal passage will occur tomorrow afternoon/evening from northwest to southeast, bringing renewed chances for rainfall alongside well below normal temperatures and cloudy conditions. This second round of rain also runs the risk of overperformance; however, the forecast has trended wetter. Totals of 0.10"-0.50" for most of the North Bay and 0-0.10" south of the Golden Gate Bridge are expected with accumulation south of the Golden Gate Bridge primarily favoring the San Francisco Peninsula Coast. Looking at the 90th percentile, totals get bumped up with up to 1.00" possible in the higher terrain of the North Bay and up to 0.50" along the San Francisco Peninsula Coast. While rainfall is expected to be beneficial, wet roadways will create slick driving conditions and increase stopping distance. Wind Advisory criteria is not expected to be met; however, gusts of 30-40 mph can be expected through gaps/passes and down the Salinas Valley.

LONG TERM

Issued at 1159 AM PDT Wed Sep 2 2026 (Friday through next Tuesday)

A cutoff low will spawn in the Pacific Northwest from remnant upper- level troughing as ridging expands westward into the Desert Southwest. The low is expected to fill through the weekend, giving the ridge increasing influence over the forecast. As such, a gradual warming and drying trend and the reformation of the marine layer is expected over the weekend. These features will also be enough to shunt moisture from Tropical Storm Marie south of the California Bight, at least for now. Even with a cutoff low in play, there is relatively good agreement in the forecast through Monday. By Tuesday, the ECMWF and GFS begin to drastically diverge on their solutions with Marie. The one to watch will be the ECMWF as it has another cutoff low digging, absorbing, and bringing what was Marie into Central California, which would be a low probability outlier at the moment. It's imperative to note that if it reaches California: Marie will no longer be tropical and the primary impact will be rainfall.

AVIATION

(18Z TAFS) Issued at 1102 AM PDT Wed Sep 2 2026

Primarily VFR conditions with MVFR ceilings over the North Bay that are expected to lift by 20z. A prefrontal band of light rain will continue to move across the Bay Area into the early afternoon with less than 0.10" of rainfall expected and minimal impacts. A very deep marine layer (~5000ft) will be compressed somewhat later today into late tonight, then deepen again by early Thursday morning as a weak cold front moves across our area and the troughing pattern persists.

Vicinity of SFO...Light rain in vicinity of the Bay Area terminals should move east by 20z. VFR is expected to prevail through the remainder of today and tonight with a chance of MVFR ceilings developing after sunrise Thursday.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the remainder of today until later tonight around midnight, when MVFR/IFR ceilings are expected to develop. and persist through the remainder of the forecast period. Confidence is higher this far south away from the more prominent influence of the approaching cold front to the north.

MARINE

(Today through Monday) Issued at 1102 AM PDT Wed Sep 2 2026

The light northwesterly breezes will continue through the week with occasional moderate gusts and slight to moderate wind driven seas. Diurnal winds gradually increase Friday afternoon, and once again Saturday especially in vicinity of Monterey Bay. Tropical cyclone activity will produce long period southerly swell for Friday through the weekend.

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...None.