Thousands of homes were under evacuation orders and warnings on Sunday from wildfires in Northern California wine country and central Oregon as crews battled the flames in dry, hot weather.

The Pickett Fire, which had charred about 10 square miles (26 square kilometers) of Napa County, was just 11% contained on Sunday, according to the California Department of Forestry & Fire Protection, or Cal Fire.

Some 190 people were ordered to leave their homes, while another 360 were under evacuation warnings as the fire threatened 500 structures near Aetna Springs and Pope Valley, about 80 miles (127 kilometers) north of San Francisco, said Cal Fire spokesperson Jason Clay.

In Oregon, the Flat Fire in Deschutes and Jefferson counties had grown to almost 34 square miles (88 square kilometers), with about 4,000 homes under various levels of evacuation notice, including 1,000 with orders to leave immediately, according to the state Fire Marshal’s Office.

Firefighters were able to cut containment lines and continued to suppress fires in some residential areas. However, they faced significant challenges Sunday with difficult terrain, low humidity and triple-digit temperatures in some areas, officials said.

Some homes have burned, and officials said they were working to confirm the status of structures.

More than 1,230 firefighters backed by 10 helicopters were battling the California fire, which began in a remote area on Thursday after a week of hot weather. The cause of the fire is under investigation.

Residents of the Western United States have been sweltering in a heat wave that hospitalized some people, with temperatures hitting dangerous levels throughout the weekend in Washington, Oregon, Southern California, Nevada and Arizona.

Clay said the weather has moderated since the California fire broke out, with Sunday’s high about 94 degrees (34 Celsius). But humidity levels were expected to drop amid increasing winds later in the day.

“That’s been a driving factor in the afternoons since we’ve seen the fire activity pick up for the last three days,” Clay said, adding that “support from all up and down California has been critical to our efforts.”

The Pickett Fire began in the same area as the much larger Glass Fire in 2020, which crossed into Sonoma County and eventually burned about 105 square miles (272 square kilometers) and more than 1,500 structures.

The 2020 blaze was driven by wind, while the current conflagration is fueled mainly by dry vegetation on steep slopes — some of it dead and downed trees left over from the Glass Fire and some of it grass and brush that grew back and then dried out again, said Clay.

The area of the Oregon fire is in a high desert climate, where dried grasses and juniper trees are burning and fire is racing through canyon areas where it’s challenging to create containment lines, said Jason Carr, Deschutes County sheriff’s spokesman.

The fire began Thursday night and grew quickly amid hot, gusty conditions. Fire officials were keeping an eye on isolated thunderstorms in Southern Oregon that could drift north on Sunday, state Fire Marshals spokesman Chris Schimmer said in a video posted to Facebook.

“If we get thunderstorms that roll through, it can … cause the fire to jump (containment) lines,” said Carr, adding the downdrafts can push fire in multiple directions.

In central California, the state’s largest blaze this year, the Gifford Fire, was at 95% containment Sunday after charring nearly 206 square miles (534 square kilometers) of San Luis Obispo and Santa Barbara counties since erupting on Aug. 1. The cause is under investigation.

Although it’s difficult to directly tie a single fire or weather event directly to climate change, scientists say human-caused warming from burning fossil fuels like coal and gas is causing more intense heat waves and droughts, which in turn set the stage for more destructive wildfires.

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Associated Press writer Christopher Weber contributed from Los Angeles.

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