San Francisco wildfire smoke forecast
The map above shows NOAA HRRR-Smoke near-surface PM2.5 for the next 48 hours, updated hourly, with active fires from NIFC and live AQI from EPA AirNow monitors. It opens over San Francisco.
San Francisco sits at the mouth of the only sea-level gap in California's Coast Range, which makes it the ventilation point for the whole Bay Area and much of the Central Valley. The marine layer that gives the city its summer fog also sets a hard lid a few thousand feet up, and that lid decides whether a smoke episode is something you see or something you breathe.
Where the smoke comes from
North Bay fires in Sonoma and Napa, Sierra fires to the east, and far-northern California fires all reach the Bay. The direction matters more than the distance: a fire 200 miles north with the right flow will affect the city more than one 60 miles east without it.
How long it lasts
Onshore flow clears the surface quickly, often in hours. The complication is that smoke can ride above the marine layer while surface air stays clean, so the sky can look apocalyptic while monitors read moderate. The near-surface forecast and the visible sky routinely disagree here, and the near-surface number is the one that matches what you breathe.
Past smoke events
September 9, 2020 is the clearest example anywhere of that split. Smoke aloft was dense enough to block sunlight and turn the sky orange all day, while surface PM2.5 across much of the city stayed in the moderate range. The October 2017 Tubbs Fire and the November 2018 Camp Fire produced the reverse: ordinary-looking skies with genuinely hazardous surface air.
Running, riding, and trailheads
The Marin Headlands, the Presidio, and Ocean Beach sit closest to the incoming marine air and usually clear first. The East Bay hills and the inland valleys hold smoke longer, so a ride over the bridge can cross an air-quality boundary in a few miles.
Reading the map
Use the layer toggle to compare NOAA HRRR-Smoke with the ECCC FireWork model. When the two disagree, treat the higher reading as the cautious call.
Near-surface is the product that maps to what you breathe and to AQI, not the high-altitude column that only tints the sunset. A sky that looks bad and a monitor that reads fine are usually both correct, and they are describing different layers of air.