Thursday, March 28

Oak Fire smoke is likely to reach the Bay Area. Here are the air quality impacts


Wildfire smoke billowing from the Oak Fire in Mariposa County was expected to drift over the Bay Area early Monday morning, air quality officials said.

An air quality advisory said the smoke was expected to stay aloft, producing hazy skies and a widespread smoky smell. The National Weather Service said people should “expect hazy and slightly red/orange-tinted skies due to this smoke.”

The smoke was also moving west over Yosemite National Park, webcams showed, with hazy skies in Yosemite Valley, where the park said air quality was rated “unhealthy” as of late Sunday afternoon.

By early Monday morning, light smoke was expected to creep into the far East Bay, including Antioch, but Jeff Barlow, lead forecaster with the weather service’s Hanford office in Kings County, said the smoke would stay aloft — 5,000 to 10,000 feet in the air , appearing as a brown cloud — and would not affect the air quality in the area.

The Oak Fire burning west of Yosemite National Park charred more than 14,000 acres as of late Sunday afternoon and was 0% contained.

Air quality north of the fire was particularly bad on Sunday, with the AirNow Fire and Smoke map showing unhealthy and very unhealthy conditions moving up to Arnold, Placerville and the eastern parts of Grass Valley.

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Pockets of hazardous air quality conditions appear in the Pollock Pines and Eldorado National Forest regions, and South Lake Tahoe showed very unhealthy conditions, while the western and eastern part of the lake has unhealthy conditions.

Orange haze fills the sky as cows graze in a pasture as the Oak Fire burns in unincorporated Mariposa County.

Ethan Swope/The Chronicle

The weather service projected that a blanket of smoke after moving into Yosemite would be over the Sierra foothills Sunday evening, with heavy smoke pushed by “downslope winds.”

In contrast to gusty conditions that fan many wildfires, high winds were not responsible for pushing the Oak Fire outward, Barlow said, adding however that dry fuel was helping the fire grow. Low humidity between 8% and 13% was also “feeding the fire,” and temperatures in the high 80s to low 90s were making it rough going for firefighters, Barlow added.

Barlow said some fire elevation thunderstorm activity was a possibility Monday and Tuesday, and that could affect the fire with potential gusting winds. Another “surge of monsoon moisture” is forecast Thursday through Friday. These thunderstorms are predicted to occur at high elevations around 8,000 feet — not uncommon in the summer in the Sierra — and not at 3,000 to 4,000 feet, where the wildfire is burning.

Kellie Hwang is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @KellieHwang


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