The Mosquito fire, which has been tearing through the Sierra Nevada foothills since last week, became California’s largest blaze of the year on Wednesday.

The fire formed on Sept. 6 and has been moving east through dry, hilly terrain northeast of Sacramento, the state capital. It made an unexpected surge on Tuesday, damaging or destroying some buildings.

By Wednesday evening it had grown to more than 63,000 acres, making it California’s largest of the 2022 season, said Kevin Tidwell, the public information officer on the Mosquito fire.

It was 20 percent contained as of Wednesday night. Cooler temperatures and higher humidity expected over the next few days are likely to help firefighting crews, and light southwesterly winds could steer flames and smoke away from nearby communities, Mr. Tidwell said in a phone interview.

Still, he added, those same winds could also give the fire fresh oxygen and push it farther east into dry forests west of Lake Tahoe that are loaded with potential kindling.

“It’s still those critically dry fuels that are the issue,” he said.

Several evacuation orders and warnings were in effect on Wednesday for Placer and El Dorado Counties. Mr. Tidwell said that while firefighting crews had made progress lately on the fire’s northern, western and southern flanks, the area was not yet safe enough for any of the more than 11,000 residents who had been evacuated to return to their homes.

California’s next-largest active blaze, the McKinney fire, became the state’s largest of the year in late July. As of Wednesday night it was just over 60,000 acres and 99 percent contained.