textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1039 PM PDT Mon Aug 31 2026

- Cooler weather continues through the week

- Beneficial wetting rain expected in the North Bay

UPDATE

Issued at 915 AM PDT Tue Sep 1 2026

The deepening trough off of the Pacific Northwest and northern California coasts is resulting in a mixing out of the marine layer and temperatures as much as 20 degrees cooler than seasonal averages. As such, ceilings have been around 3000 ft or greater much of the night and into early this morning. Expecting these low clouds to mix out and bring mostly sunny skies this afternoon. The exception will be over the North Bay where high level clouds will persist through much of the day. So updates are anticipated at this time as the ongoing forecast remains on track.

RGass

SHORT TERM

Issued at 1039 PM PDT Mon Aug 31 2026 (Tonight through Wednesday)

Cool and wet. A deep 500 mb trough will slowly move towards the coast over the next 24 hours. The marine layer is currently 3,200 ft deep as measured by the 00Z OAK sounding. This deep marine layer, combined with the approaching trough, will very likely bring some coastal drizzle Tuesday morning. Afternoon temperatures will be 5-15 degrees below normal as the 850 mb temperature drops below 10C/50F for the first time since May. By Tuesday night a very weak cold front will bring a good chance for light rain to the North Bay. This front will move southward through the night and into Wednesday morning, bringing lower rain chances to the rest of the Bay Area and Central Coast. Wednesday will be similar to Tuesday with cool temperatures and another chance for rain in the North Bay overnight as a second disturbance moves through.

LONG TERM

Issued at 1039 PM PDT Mon Aug 31 2026 (Wednesday night through next Monday)

Rain chances peak Thursday morning with an 90% chance of precipitation in the North Bay, and a 70% chance of at least 1/10" at Santa Rosa. Again the rain chances fall off quickly as the system moves south, but there's a decent chance (20-50%) for lighter rain across the cwa. The cooler weather will continue through Friday as the trough produces a cut-off low near the Pacific Northwest. By the weekend, high pressure will build over the desert SW. The interaction between the low pressure to the NW and high pressure to the SE brings more uncertainty to the forecast. If the trough is dominant the cooler weather will stick around, if not then we can expect a warming trend this weekend.

The National Hurricane Center continues to track Invest 95E in the Eastern Pacific. While there is now a 100% chance of tropical cyclone formation over the next 48 hours, the circulation center was displaced from the thunderstorm activity and it struggled to get organized today. The eventual track of this system is still uncertain, with the ensembles showing a bi-modal solution. One of these outcomes would bring wind and rain to Southern California around Sunday or Monday. Either the PNW cut-off low will move far enough south to pull the decaying tropical cyclone towards Southern California, or high pressure will build south of the low, forcing the storm harmlessly to the NW. While there is a lot of hype around different deterministic solutions, it's much more appropriate to look at ensembles in this time range. Both the GEFS and ECMWF ensemble show a 20-30% chance of tropical depression level impacts in Southern California, and a 10-20% chance of tropical storm type impacts. Even in the worst case scenario, our cwa wouldn't get nearly as much rain or wind as Southern California. The current high end scenario (90th percentile) would bring 1/4" of rain to the Central Coast. The most likely outcome is no significant impacts, and the ensembles have trended more in that direction over the last 24 hours. There is virtually no chance for hurricane impacts in California. It's worth watching if another system forms behind 95E, as persistent troughing could keep the door open through next week.

AVIATION

(18Z TAFS) Issued at 1006 AM PDT Tue Sep 1 2026

VFR conditions are expected to prevail through the forecast period for all terminals. A deepening trough will continue to mix out lingering low level clouds by early afternoon.

Vicinity of SFO...VFR with occasionally breezy onshore flow this afternoon and early evening.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR is expected to prevail through the forecast period with a slight chance of MVFR ceilings developing after midnight.

MARINE

(Today through Sunday) Issued at 915 AM PDT Tue Sep 1 2026

Light northwesterly breezes will persist through the week with occasional moderate breezes. Slight to moderate wind driven seas will continue through the week with tropical cyclone activity producing long period southerly swell by the end of the week into the weekend.

MTR WATCHES/WARNINGS/ADVISORIES

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