Wildfires in California wine country and Central Oregon grew overnight, prompting hundreds of evacuations as firefighters worked Sunday to try to contain the blazes amid dry, hot weather.

The Pickett Fire in Napa County had grown to more than 10 square miles (26 square kilometers) and was 11% contained as of early Sunday, according to the California Department of Forestry & Fire Protection.

About 190 people were ordered to leave their homes, while another 360 were under evacuation warnings as the fire threatened about 500 structures near Aetna Springs and Pope Valley, said Jason Clay, spokesman for Calfire Sonoma Lake-Napa Unit.

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

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

Clay said the weather has moderated since the fire broke out, with Sunday’s high expected to be 94 degrees (34 Celsius). But as the day goes on, humidity levels were expected to drop and the winds to pick up in the afternoon.

“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 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.

That fire was driven by wind, while the current fire is fueled 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.

In Oregon, the Flat Fire in Deschutes and Jefferson counties had grown to almost 34 square miles (88 square kilometers), with no containment, and threatened nearly 4,000 homes, according to the state Fire Marshal’s Office. About 10,000 people were under some sort of evacuation notice.

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, spokesman Chris Schimmer said in a video posted to Facebook.

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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