Smoke blankets the town of Felton during the CZU August Lightning Complex Fires on Thursday, Aug. 20, 2020 in Felton, CA.

Smoke blankets the town of Felton during the CZU August Lightning Complex Fires on Thursday, Aug. 20, 2020 in Felton, CA.

Photo: Kent Nishimura / Los Angeles Times

Smoke blankets the town of Felton during the CZU August Lightning Complex Fires on Thursday, Aug. 20, 2020 in Felton, CA.

Smoke blankets the town of Felton during the CZU August Lightning Complex Fires on Thursday, Aug. 20, 2020 in Felton, CA.

Bay Area air-quality forecast for the week ahead

Containment on multiple wildfires around the Bay Area is increasing, but these massive blazes are still burning and expected to continue to pump out smoke in coming days. Poor air quality will remain a problem until the fires are extinguished.

"Expect haze and patches of smoke until the fires are suppressed," said National Weather Service forecaster Drew Peterson.

The Bay Area Air Quality Management District has a Spare the Air alert in effect through at least Tuesday, warning of a high amount of particulate matter pollution in the air. The Air Quality District advises residents to go inside if they smell smoke outdoors. And keep windows and doors closed.

It's difficult to pin down air-quality forecasts as a slight shift of wind can push a mass of smoke from one place to another in minutes, but Peterson said coastal areas are likely to see cleaner air than inland valleys through Wednesday or Thursday due to an ocean breeze pushing smoke east.

"What I see today is continued onshore flow that will push the smoke into the Central Valley," said Peterson. "Immediately in the area of a fire, it could also be smokey. Onshore flow remains in the forecast through Tuesday and even Wednesday. On Thursday there could be a light onshore flow."

The ocean breezes usually don't pick up until the afternoon, so coastal areas are likely to see their worst air quality in the morning hours. As the winds develop, skies will clear. The far East Bay, mainly the area east of Danville and down in the mountainous regions of Santa Clara County, could see unhealthy conditions in the afternoon.

In the first half of the week, a marine layer will keep temperatures along the coast fairly mild with afternoon highs in the 60s to low-70s. Temperatures in the inland valleys will be in the 80s and 90s. The cool, mild weather will help quell the wildfires.

Another interesting piece of the forecast in the first half of the week is northeasterly winds, a.k.a. offshore flow, are expected to develop over the North Bay. These so-called Diablo Winds usually pick up in the fall and lead to extreme fire conditions, but Peterson said the winds forecast in coming days will be extremely light and the NWS is unlikely to issue a Red Flag Warning.

A ridge of high pressure will be developing through the week, reaching full strength over the weekend and pushing up temperatures and suppressing the marine layer. The recent spell of cool temperatures and heavy fog has been beneficial to firefighting efforts and the shift in the weather could promote fire activity.

Winds will also calm as the high-pressure builds and the smoke will become more stagnant, with a tendency to settle over an area rather than move around, Peterson said.

The high pressure will build through the weekend, and inland temperatures could reach the 100s by Saturday with more warming on Sunday and Monday. "We could potentially be looking at record-breaking temperatures this weekend and into next week," Peterson said.

Amy Graff is the news editor for SFGATE. Email her: agraff@sfgate.com.

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Bay Area air-quality forecast for the week ahead - SF Gate