Poor weather conditions hamper firefighting efforts across California.

U.S.|Poor weather conditions hamper firefighting efforts across California.

• Aug. 26, 2021, 7:06 a.m. ET

On Wednesday, more than 14,000 firefighters were on the front lines of 12 large wildfires in California that have burned more than 1.6 million acres, fire officials said.

Unfavorable weather conditions continue to trouble crews battling the Caldor fire near Sacramento. Earlier this week, fire officials said the blaze had become a top priority after it burned more than 100,000 acres in 10 days. By Wednesday night, the fire had burned 134,000 acres and was 12 percent contained, according to a New York Times wildfire tracker. More than 450 homes had been destroyed and another 17,000 other structures were threatened, reported Cal Fire, the state’s firefighting agency.

Fire officials on Wednesday night said that gusty winds combined with critical fuel conditions had threatened an area north of Highway 50, one of the main routes between Sacramento and the Lake Tahoe area.

Farther north, the Dixie fire, the second-largest on record in California, remains a threat to communities. That fire started six weeks ago and has since burned 747,000 acres, including the town of Greenville. It is 45 percent contained. Evacuation orders remain in place for some areas around the fire. Some residents have ignored evacuation orders, staying to tend to their cattle or to protect their homes.

Amid strained firefighting resources and a crippling drought made worse by climate change, the South fire began on Wednesday near San Bernardino. The fire has burned more than 500 acres at zero percent containment and has prompted 1,000 households to evacuate, according to Cal Fire. The blaze is threatening high voltage transmission lines and at least 600 structures. About 86,000 people live within five miles of the fire, according to the Times’s fire tracker.

Other major blazes across California remain active, including the McFarland fire, which has burned 122,000 acres, and the Monument, which has burned 154,000 acres.

An excessive heat warning is in place through Sunday for areas around San Diego, the National Weather Service said. Elevated fire weather conditions, with low relative humidity values, were expected through Saturday for communities in central California. Points north are under a heat advisory through Saturday night, with temperatures forecast to reach 110 degrees. Gusty winds were expected to develop by Friday across the Sacramento Valley.

The fire potential in most of California’s mountains and foothills is forecast to be higher than normal through September, and through October in areas prone to offshore winds, the National Interagency Fire Center said this month.