Air quality advisory issued as smoke from Oak Fire near Yosemite forecast to reach Bay Area

The Bay Area Air Quality Management District issued an air quality advisory as smoke from the Oak Fire in Mariposa County is forecast to waft over the San Francisco Bay Area on Monday.

"We don't expect air quality to be unhealthy, but we do expect smoky, hazy skies and potentially higher levels of smoke at higher elevations," Kristine Roselius, a spokesperson for the Bay Area Air Quality Management District, told SFGATE on Sunday. "If you're on Mount Tam, for instance, you may have unhealthier smoke levels at that elevation."

The wildfire that broke out on Friday afternoon near Midpines, a town just south of Yosemite National Park, swelled from 1,600 to 14,281 acres over the weekend, forcing thousands of people to evacuate their homes. There is no containment at this time.

That smoke has already drifted nearly 200 miles north to South Lake Tahoe, where air quality was considered "hazardous to unhealthy" on Sunday afternoon, the Tahoe Daily Tribune reported. "High concentrations of near-surface smoke" were also visible from the Eastern Sierra to Southern Douglas County, the outlet said.

Roselius predicts the smoke will impact the East and North bays first before lingering over the rest of the Bay Area. She also noted that while the smoke is expected to remain aloft — "not where we live and breathe" — residents should go inside if they see or smell it, and keep windows and doors closed if temperatures allow.

Drew Peterson, a meteorologist with the National Weather Service, said the smoke may shift toward the west on Monday evening into Tuesday morning and anticipates surface smoke over the North and East Bay mountains. The weather service is unable to determine air quality forecasts more than 48 hours in advance, and predictions can change depending on factors like the spread and containment of a wildfire.

"It's a very dynamic situation," Peterson said. "But I expect we'll continue to see smoke along the periphery mid-week and beyond."

If the smoke sticks around at a higher altitude, the nocturnal inversion from the marine layer can act as a barrier and prevent it from reaching lower points of the atmosphere, limiting some of the more noticeable impacts as the wind transports it through the air.

"The flow looks vigorous enough that it will push [the smoke] up and over the area," Peterson said. "It'll probably be hazy. You'll see an orange tint to the sun. But I'm not ready to say we're going to see a lot of smoke mixing down to the lower surface area, as long as we keep getting that movement."

Circumstances can change rapidly. Roselius advised that residents check the AirNow Fire and Smoke Map created by the Environmental Protection Agency and the United States Forest Service for air quality updates

"Wildfire smoke is very unpredictable. It's hard to forecast," Roselius said. "We're watching it very carefully. If it continues, we'll call another air quality advisory, and if we expect it to be unhealthy, we'll call a Spare the Air alert."