According to the California Department of Forestry and Fire Protection, the Dixie fire has gained ground and was only 21 percent contained as of Sunday.
Crews and officials battling a large fire that has incinerated more than 77,000 hectares (190,000 acres) in northern California braced for the possibility that smoke columns could spawn lightning storms capable of igniting more blazes.
The swarming Dixie fire in Butte County, north of Sacramento, gained ground on Saturday and was only 21 percent contained as of Sunday, according to the California Department of Forestry and Fire Protection.
The Dixie fire joined with another one nearby on Saturday night, and firefighters have struggled to contain the blazes that have triggered evacuations in several communities.
Lightning storm fears
"There is a high probability for the smoke columns to develop what we call a pyrophoric (cloud)," fire behaviour analyst Dennis Burn said in a video message posted on the Facebook page of Lassen National Forest.
Large fires like the Dixie fire and Oregon's Bootleg fire, a massive blaze that has blackened more than 408,000 acres and was 46 percent contained as of Sunday, can at times generate their own weather, like lightning storms.
With the Dixie fire encroaching, the Plumas County Sheriff's Office issued mandatory evacuation orders for the eastern shore of Lake Almanor where "personnel are conducting door to door notifications."
An evacuation shelter was established in the city of Susanville, and five other areas were placed under evacuation warnings.
The fire also prompted evacuation orders in several small mountain communities and along the west shore of Lake Almanor, a popular resort area. About 10,000 homes remained under threat, officials said.
Elsewhere in California, the 269-square-kilometer (104-square-mile) Tamarack fire south of Lake Tahoe continued to burn through timber and chaparral and threatened communities on both sides of the California-Nevada state line . The fire, sparked by lightning July 4 in Alpine County, California has destroyed at least 23 buildings, including more than a dozen in Nevada. It was 27 percent contained on Sunday, and officials were able to lift evacuation orders.
Oregon's bootleg fire
In Oregon, crews battling the Bootleg fire faced the "warmest and driest" day for the next several days, fire officials said in an update on Sunday.
More than 2,200 personnel were combating the Bootleg fire, officials from an interagency task force said.
"Evacuations are dynamic," the officials said, publishing an interactive map with warnings such as "Go (Leave immediately)" and "Be Set (Prepare to leave at a moment's notice)."
The Bootleg fire is one of more than 86 large active wildfires in 12 states that have charred more than 1.4 million acres in recent weeks, according to the National Interagency Fire Center (NIFC) in Boise, Idaho.
The conflagrations in the US West, marking a heavier-than-normal start of the wildfire season, have coincided with record-shattering heat that has baked much of the region in recent weeks and caused hundreds of deaths.