textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1209 AM PDT Wed Aug 26 2026

- Temperatures near to slightly below seasonal averages persist within the shallow marine layer through Thursday

- Seasonably warm and very dry conditions continue above 1000 feet and the far interior through Thursday

- Pattern change Friday into the weekend brings cooler temperatures and moderate potential for tropical moisture

SHORT TERM

Issued at 1209 AM PDT Wed Aug 26 2026 (Today and tonight)

Stratus clouds are developing at the immediate coast and will expand into the coastal valleys through the night, before mixing out Wednesday morning. The weather pattern today remains dominated by the balance between ridging in the Desert Southwest and troughing in the eastern Pacific, with a slight edge to the ridging as reflected in a general warming trend across the region. Highs in the inland valleys reach the middle 80s to the middle 90s, up to 106 within the warmest regions of southern Monterey County, with the Bays reaching the middle 70s to the middle 80s and the Pacific coast remaining rather cool in the lower to middle 60s. A gentle to moderate onshore breeze develops in the afternoon and evening hours with gusts of 20 to 30 mph at the coast, through gaps and passes, and within the Salinas Valley. The marine layer will remain around 1000-1500 ft today, with warm and dry conditions above the marine layer inversion. See the FIRE WEATHER section for the implications for local fire weather concerns.

LONG TERM

Issued at 1209 AM PDT Wed Aug 26 2026 (Thursday through Tuesday)

The ridging remains in place through Thursday with temperature around the same as today's before the trough over the eastern Pacific begins to migrate eastwards late Thursday into Friday, starting a cooling trend that will last through the early part of next week. As the trough moves into the West Coast, it will pull in tropical moisture partially from what would be the remnants of Tropical Storm Iselle and direct it towards the state. The model trend for steadily increasing Precipitable Water values has continued to play out, with ensemble model probabilities suggesting that Oakland is likely to see precipitable water values exceeding 1.0 inches on Friday morning. For context, the 90th percentile value for precipitable water at OAK is 1.04 inches, and pretty much all the deterministic models that go out this far have OAK exceeding this value, with some of the wetter models making a run for or exceeding the daily maximum value, which for the 12Z (5 AM PDT) soundings on August 28, would be 1.24 inches. This kind of setup would definitely bring high clouds to the region and also brings the risk of high-based rain showers and thunderstorms to the region. One of the big caveats of this risk, especially as it pertains to thunderstorms, is that model output also suggests that instability is lacking with the European model showing virtually no CAPE anywhere within the atmosphere, surface or elevated. We will continue to monitor the evolution of this setup closely.

The incoming trough will also lead to an tightening of the pressure gradient, which in turn will lead to breezier winds Friday into the weekend. Gusts will rise to 25 to 35 mph along the coast and through favored gaps, valleys, and passes. The troughing pattern will continue to develop into the early part of next week, when temperatures will dip 5 to 15 degrees below the seasonal average, with highs in the 70s to lower 80s in the interior valleys. The current forecast has some rain chances returning towards the middle of next week, but this is critically dependent on the future evolution of the situation in the tropical East Pacific, and as a result the confidence in this forecast is very low at this time.

AVIATION

(12Z TAFS) Issued at 419 AM PDT Wed Aug 26 2026

The mid/high clouds moved out of our area and the marine layer quickly reorganized and made a push inland. IFR/LIFR has developed for a majority of the terminals with KLVK likely to be the only site impacted by stratus ceilings through the remainder of the forecast period.

Vicinity of SFO...A steady fetch of onshore flow channeling through the Bay Area was interrupted briefly by high clouds earlier Tuesday night into this morning but has now begun to increase in coverage. VFR ceilings are expected by mid-morning as stratus retreats back toward the coastline.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...IFR/LIFR ceilings developed in the wake of upper level clouds, after is seemed possible stratus might not fill in. Coverage is still not as extensive as normally seen at this time, with VFR expected by mid to late morning. IFR/LIFR ceilings aren't expected to return until around sunset.

MARINE

(Today through Monday) Issued at 419 AM PDT Wed Aug 26 2026

Fresh to strong northwest winds will continue today into the weekend with moderate wind driven seas. A long period southerly swell will build late in the week becoming 17-18 seconds by Friday and persist through at least early Sunday.

FIRE WEATHER

Issued at 1209 AM PDT Wed Aug 26 2026

Not much has changed in terms of the fire weather threat, with near critical fire weather conditions persisting in the higher elevations above 1000 feet through Thursday due to warm and dry conditions. Overnight humidity recoveries remain poor to very poor within these areas and the impact of the marine layer inversion leads to temperatures warmer than the seasonal average, especially within the Santa Lucia range and the interior Central Coast where temperature are running as much as 15 to 20 degrees above the seasonal average. Model output suggests that an offshore flow has set up over the Big Sur coast at the 925 mb level, supporting the risk for overnight nocturnal drying in the interior Central Coast and particularly surrounding the Timber Fire. Last night I had noted that the southwest winds seemed to bring in more moist air into the Santa Lucia range, and that the overnight diminishing of winds when combined with the offshore push led to an unusual situation where the maximum daily relative humidities took place during the day. This remains the case, up until the ridgeline parallel to the Big Sur coast when the southwest winds begin to downslope and dry the region. Unfortunately there aren't a lot of weather station in these areas to verify the conceptual model. Smoke transport from the Timber Fire will continue to peak in the afternoon and evening with the plume spreading towards the Salinas area. Friday into the weekend, a pattern change should allow for some relief as an upper level trough comes into the region bringing cooler temperatures and a deeper marine layer.

DialH

MTR WATCHES/WARNINGS/ADVISORIES

CA...None. PZ...Small Craft Advisory until 9 AM PDT Friday for Pigeon Pt to Pt Pinos 0-10 nm-Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Pinos to Pt Piedras Blancas 0-10 nm.