textproduct: San Francisco Bay Area

KEY MESSAGES

Updated at 1245 AM PDT Tue Aug 11 2026

- Up to a 15% chance for elevated rain showers/thunderstorms Wednesday across the Central Coast

- Cooling trend through Thursday, gradual warming trend Friday through the weekend will bring well below normal temperatures

- Minor coastal flooding for bayshore locations along the San Francisco Bay, San Pablo Bay, and Monterey Bay through Thursday morning

SHORT TERM

Issued at 1245 AM PDT Tue Aug 11 2026 (Today and tonight)

Cooling trend continues today as upper-level shortwave troughing deepens off the West Coast. The associated lift will deepen the marine layer and bring a chance for drizzle to coastal areas. The Timber Fire in Big Sur will continue to bring smoke and haze to the Central Coast via light southwesterly transport winds from the aforementioned troughing. Ample moisture and sufficient instability will bring up to a 10% chance for elevated rain showers tomorrow. The relatively greatest chances are across the Interior Mountains of Monterey and San Benito Counties. The primary hazard would be erratic/gusty outflow winds with dry low levels and DCAPE near 1000 J/kg. Minor coastal flooding is expected during the highest high tide (evening/overnight) for bayshore locations along the San Francisco Bay, San Pablo Bay, and Monterey Bay through Thursday morning.

LONG TERM

Issued at 1245 AM PDT Tue Aug 11 2026 (Wednesday through Monday)

A reinforcing trough Wednesday will bring widespread below normal temperatures, deepen the marine layer further, and bring chances for coastal drizzle through Thursday. It may also act as the trigger for elevated rain showers/thunderstorms as it overlaps with an influx of monsoonal/sub-tropical moisture and sufficient instability. The best chances are across the Central Coast on Wednesday, more specifically the southern and eastern portions. While confidence is low, this would be a high-impact scenario with erratic/gusty outflow winds and the potential for new fire starts. A gradual warming trend is expected Friday through the weekend as upper-level ridging builds in from the southeast; however, temperatures will still remain well below normal.

AVIATION

(18Z TAFS) Issued at 1133 AM PDT Tue Aug 11 2026

Stratus has retreated to the coastline where it'll remain for the rest of the day. Widespread VFR throughout the day with moderate onshore breezes increasing in the afternoon before easing around sunset. The marine layer pushes onshore again, impacting coastal sites first before sunset. The stratus will then continue its push to inland sites overnight, around/after midnight. Medium confidence on how expansive the stratus layer will be tonight considering the transition period we are in with the passing upper level trough. The trough has the potential to deepen the marine layer up to 1800-2000 feet. As a result, low confidence on whether SJC will develop an MVFR ceiling early Wednesday morning as it is dependent on marine layer depth. Overall, expect a mixture of low-end MVFR to IFR ceilings with a similar clearing time as today (17-18Z Wednesday).

Vicinity of SFO...VFR into the evening with moderate northwest winds increasing this afternoon to 15-18 kt. Higher confidence for OAK to develop an MVFR ceiling around midnight this TAF period. Low to medium confidence for SFO to develop a ceiling given the recent trend, but hinted at the potential for MVFR ceilings to develop shortly after OAK. Any cloud ceiling that develops south of the Bay Bridge is expected to clear late Wednesday morning.

SFO Bridge Approach...Similar to SFO.

Monterey Bay Terminals...VFR through the afternoon with smoke/haze in the local airspace due to a nearby fire on the Big Sur coastline. Onshore winds increase through the afternoon and decrease through the evening/overnight. Low-end MVFR to IFR ceilings are expected to impact both terminals early this evening before sunset. Coastal drizzle is possible in the overnight hours, but currently have low confidence on exactly when and how long it will last.

MARINE

(Today through Sunday) Issued at 404 AM PDT Tue Aug 11 2026

Fresh to strong northwest winds will continue to produce rough seas across the northern outer waters through Thursday. Long period southerly swell will gradually increase from 15 seconds through the middle of the week, up to 17 to 19 seconds by Friday into Saturday.

FIRE WEATHER

Issued at 529 AM PDT Tue Aug 11 2026

There is up to a 15% chance for elevated rain showers/thunderstorms Wednesday across the Central Coast. Lightning was occurring with a very slow moving 500 mb low pressure system located 400 miles southwest of Monterey this morning. This low is forecast to move very slowly northeastward today and tonight then start to move a little quicker to the northeast Wednesday guided by strengthening subtropical jet stream winds (polar jet stream winds will be located to its northwest). This will be part of the evolving eastern Pacific trough pattern this week mentioned in our discussion. We'll monitor this low closely for mainly mid level convective potential because it'll be located along and moving with a relatively sharp moisture gradient. This can favor convection by locally steepening lapse rates if there is upward forcing of a moist layer below a dry layer. The good news is the very development of this trough this week will be resulting in deep layered thermal troughing, increasing the marine layer depth, the inland extent of marine influence including stratus, fog and drizzle which will reduce surface convective potential inland, that is, reducing the need for the atmosphere to do work and overturn a more deeply unstable atmosphere (to restore stability). This bears watching closely if only because summer season features moving north from lower latitudes are complex, potentially dynamic changing features even when 500 mb heights are greater than 580 decameters.

MTR WATCHES/WARNINGS/ADVISORIES

CA...Coastal Flood Advisory until 2 AM PDT Thursday for CAZ006-506- 508-529-530.

PZ...Small Craft Advisory until 9 AM PDT Thursday for Pt Arena to Pt Reyes 10-60 NM.