textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 125 PM PDT Thu Aug 27 2026

- Slight chance of thunderstorms through Friday afternoon, especially across the Central Coast

- Cooling trend continues Friday into next week

SHORT TERM

Issued at 125 PM PDT Thu Aug 27 2026 (This evening through Friday night)

Looking at satellite imagery, seeing more widespread mid-to-high level cloud cover spreading across the Central Coast and southern portion of the greater San Francisco Bay Area. The greatest potential for high-based convection will be across the Central Coast as the OAK Upper Air sounding reported MUCAPE (instability aloft) slightly greater than 400 J/kg. This is also where the CAMs and higher resolution deterministic models show the greatest MUCAPE values today through early Friday morning. Thus, have added isolated thunderstorms to the official forecast for the Central Coast. Further north across the Bay Area, seeing less threat for thunderstorms, yet remains a non-zero chance.

The Precipitable Water (PWAT) values increase to around or slightly above 1.5" across the Central Coast by Friday morning with a greater potential for wetting rains. However, rainfall amounts are projected to largely be less than 0.10" throughout this event. Thus, we have issued a Red Flag Warning for much of the Central Coast including the Santa Cruz Mountains from 5 AM to 3 PM Friday. Fuels remain dry from the recent warm and very dry conditions above the marine influences, especially in areas above 1000 feet in elevation. This is also where the CAMs have the greatest instability on Friday. Given the Timber and Plaskett fires ongoing, any lightning strikes and/or erratic/gusty outflows would make for difficult firefighting efforts. Will closely monitor the latest forecast models and adjust accordingly.

As the mid/upper level trough deepens off of the Pacific Northwest coast Friday evening into Saturday morning, expecting this deeper moisture plume to shift eastward resulting in PWAT values lowering to near 0.50". Thus, ending the threat for high-based convection. The mid/upper level low off of the Pacific Northwest will push inland Friday night into Saturday, leading to a tightening pressure gradient which will result in breezier winds Friday and into the weekend. Thus, wind gusts are forecast to reach 25 to 35 mph along the coast and through favored gaps, valleys, and passes. This pattern will also usher in cooler temperatures. Zonal flow develops over the weekend holding temperatures steadily below normal.

LONG TERM

Issued at 125 PM PDT Thu Aug 27 2026 (Saturday through next Wednesday)

A reinforcing trough deepens off of the Pacific Northwest coast by Monday, allowing afternoon temperatures to be some 5 to 15 degrees below seasonal averages. The current forecast has the potential for rain showers returning towards the middle of next week. However, the evolution of things across the tropical Eastern Pacific remains in question, mainly in the form of remnant tropical moisture to be pulled in from the south. Thus, forecast confidence remains low at this time.

AVIATION

(06Z TAFS) Issued at 925 PM PDT Thu Aug 27 2026

It's VFR with widespread mid and high level clouds over much of the forecast area. High based showers have decreased in coverage. A few light showers/sprinkles reached the ground over the north Central Coast based on earlier webcam and spotter reports. Increased cloud cover i.e. water vapor will interfere with and decrease radiative cooling; coastal stratus and fog will be limited tonight and Friday.

Vicinity of SFO...VFR. A few showers are possible tonight and/or Friday. Currently, the 06z TAF advertises vicinity showers (VCSH) 11z-20z Friday. West to northwest wind 8 to 14 knots.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR. Vicinity showers (VCSH) tonight, with tempo showers 10z-15z Friday morning and low confidence if showers will continue during late Friday morning. Winds will be a mix of west to northwest 5 to 15 knots and light and variable.

MARINE

(Tonight through next Wednesday) Issued at 918 PM PDT Thu Aug 27 2026

Northwest breezes gradually diminish to moderate by Monday. Moderate wind driven seas prevail into next week. A long period southerly swell impacts our coastal waters by Friday and persists into the weekend.

FIRE WEATHER

Issued at 125 PM PDT Thu Aug 27 2026

One more day of near-critical fire weather conditions above 1000 feet, especially across the Central Coast, as warm and dry conditions continue above the marine layer inversion and overnight humidity recoveries remain poor into Friday morning. There still is a non-zero chance for thunderstorms across the Central Coast today through tonight. By tomorrow, with the increasing potential for lightning, we have issued a Red Flag Warning for much of the Central Coast including the Santa Cruz Mountains from 5 AM to 3 PM Friday given the low confidence for wetting rains to develop. By Friday night and into the weekend, the cooling trend will continue and bring cooler temperatures and likely a deeper marine layer, bringing progressively more relief to some of the higher elevations.

RGass

MTR WATCHES/WARNINGS/ADVISORIES

CA...Red Flag Warning from 5 AM to 3 PM PDT Friday for CAZ512-516-517- 528>530.

PZ...Small Craft Advisory until 9 AM PDT Saturday 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.