"That's the biggest question," fire spokeswoman Alissa Tanner said. "If the thunderstorms will just be rain and not gusts of winds that will be a real blessing. If not, then it could spread the fire in many different directions."
Among nearly a dozen major wildfires burning across the state, a 66-square-mile blaze in Plumas National Forest has proven problematic given the remote, rugged location. More than 900 homes were under threat, and authorities have urged residents to leave.
The National Weather Service expected isolated thunderstorms for the remote area, but only a 20 percent chance of precipitation. Crews re-established containment lines on Wednesday, but officials were concerned about the stormy forecast, Tanner said.
Some 8,000 firefighters were battling California's largest wildfires, said state fire spokesman Daniel Berlant. Fire officials issued a statewide burning ban Wednesday that will stay in effect pending a significant change in the weather or the end of fire season.
Elsewhere in Northern California, firefighters made significant progress against a wildfire in Lake County, despite dry weather and triple-digit temperatures. Hundreds of evacuees were allowed to return home after the blaze burned more than 12 square miles and threatened nearly 500 homes in the Spring Valley community.
"We're definitely getting the upper hand on this fire," Berlant said.
In Southern California, wildfires threatened dozens of homes in the midst of a brutal heat wave.
In rural San Diego County, a group of five wildfires caused by lightning burned more than 24 square miles of wilderness, state fire Capt. Mike Mohler said. Evacuation orders covering about 180 homes and 400 residents were issued for the communities of Ranchita and Santa Fe.
The two largest fires were above the desert floor in an area subject to erratic winds. Forecasts called for a return of monsoonal moisture that could create thunderstorms with even more erratic winds Thursday, Mohler said.
Meanwhile, a 4 1/2-square-mile blaze in the foothills of Riverside County's San Jacinto Mountains threatened 47 homes, though officials lifted an evacuation order Wednesday. The fire near the community of Aguanga, east of Temecula, burned four structures, including at least one home.
A resident living in a trailer was seriously burned and a second resident received lesser injuries after the fire broke out Tuesday, authorities said. Two firefighters received minor injuries.
Elsewhere in Southern California, military helicopters dropped water on two fires that blackened more than 12,000 acres in the rugged Kern County mountains above the Mojave Desert about 80 miles north of Los Angeles. The fires forced the Bureau of Land Management to temporarily close about 20 miles of the popular Pacific Crest Trail, which runs through three western states between Canada and Mexico.
Berlant said officials were concerned that wildfire season began earlier than usual in the state.
"We have definitely seen an increase in fires this season in comparison to previous years," Berlant said. "Most of the damaging fires happen in September and October, not during the summer months."
He said the rest of the region also has been hit with fires relatively early in the season.
"We're starting to see the same level of activity that's been occurring in Arizona, Colorado and New Mexico," Berlant said. "We're just like the rest of the West; We continue to be hot and dry, just like them."
Associated Press writer John Antczak in Los Angeles contributed to this report.