Breaking News Emails

Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.
 / Updated 
By Phil Helsel

Cooler temperatures helped California firefighters make progress battling a huge wildfire northwest of Sacramento, but officials warned Wednesday that thunderstorms this week could spark more blazes in the northern part of the state.

Nearly 3,500 firefighters were trying to tame the Rocky Fire in Lake, Yolo and Colusa counties, which has burned 68,300 acres and is 20 percent contained. The fire has been burning for seven days.

A car burned in the Rocky Fire sits near Lower Lake, Calif., Tuesday, Aug. 4, 2015.Jeff Chiu / AP

Evacuation orders that have sent around 13,000 from their homes remain in effect, the California Department of Forestry and Fire Protection, also known as Cal Fire, said Wednesday.

"The cooler temperatures really aided firefighters in their efforts," Cal Fire spokesman Daniel Berlant said Wednesday. But the heat was expected to return and the humidity to decrease later Wednesday, he said.

The Rocky Fire has destroyed 39 homes and threatens nearly 7,000 other structures, Cal Fire said. There were 23 major wildfires burning across California, which is in its fourth year of a historic drought that has left vegetation bone dry and exacerbated wildfire conditions.

Thunderstorms are forecast for northern California Thursday, raising fears that lightning strikes could ignite more fires.

Some of the wildfires, like the so-called Humboldt Lightning Fires in the northwest part of the state, are not one fire but a "complex" of 70 lightning-sparked blazes, Berlant said. The Humboldt fires have burned 3,700 acres since Thursday and are 30 percent contained.

More than 10,000 firefighters were battling wildfires across the state Wednesday, Cal Fire said. The effort includes 770 fire engines, 153 bulldozers, 57 helicopters and dozens of aircraft, including air tankers from the California National Guard.

"We’re hitting these fires with everything we have," Berlant said.