Smoke from the Timber Fire in Big Sur has drifted into Contra Costa County as the wildfire grew beyond 23,000 acres, with air-quality conditions capable of changing quickly as winds shift.

The Timber Fire, which started Aug. 8 southeast of Loma Vista, had burned 23,343 acres and was 26% contained Friday, Aug. 28, according to CAL FIRE. The blaze grew roughly 4,000 acres Thursday, Aug. 27, jumping from about 19,000 acres in the morning to more than 23,000 by evening, Cal Fire Battalion Chief Josh Silveira told the Los Angeles Times.

The Timber Fire was California’s third-largest wildfire of the year as of Thursday, KQED reported.

Smoke from the blaze has been traveling northward into the East Bay, reaching Contra Costa County on at least Aug. 25 and Aug. 26, according to Claycord.com. NOAA satellite imagery from Aug. 25 confirmed the Timber Fire was producing heavy smoke moving toward the region, Claycord reported.

No Spare the Air Alert was in effect for Friday, Aug. 28, according to the Bay Area Air District. The district cautions that wildfire smoke conditions can change quickly depending on wind direction.

Cal Fire public information officer Ahmad Toure told KQED that Big Sur's terrain has hampered crews since the fire ignited nearly three weeks ago.

"There are intersecting river valleys, and it's really hard to get fire personnel and heavy equipment in those areas," Toure said. "It's actually very dangerous."

A second wildfire, the Plaskett Fire, started Aug. 26 in southern Monterey County. As of Friday, CAL FIRE listed the fire at 2,774 acres with no containment.

About 600 residents total received evacuation orders from the two fires combined, according to Silveira.

Critical fire weather has driven the Timber Fire's growth. The incident entered its 10th consecutive day of relative humidity below 30% on Aug. 27, with overnight humidity recoveries in the upper teens and temperatures near 80 degrees, Cal Fire reported.

A National Weather Service red flag warning took effect Friday for portions of the Central Coast because of the potential for lightning and strong winds, CBS News Bay Area reported.

Residents can check current air quality conditions at baaqmd.gov or airnow.gov.