Strong Winds Prompt Wildfire Warnings for Millions in California The first Santa Ana winds of the season are arriving this week in Southern California, where the most severe warnings were in place for Thursday and Friday.

The first strong winds of the season are hitting Southern California this week, bringing warmer temperatures, drier air and a greater risk of wildfires. Forecasters warned that a single spark could turn into a destructive fire.

The risk of wildfires reaches to the far northern part of the state, but the experts said the most extreme conditions were expected in the valleys and mountains of Ventura and Los Angeles Counties, particularly in Santa Clarita, Thousand Oaks and Simi Valley, just west of Los Angeles.

The National Weather Service issued a series of red flag warnings for Thursday, Friday and Saturday, a signal that weather experts and emergency officials are worried that fires could start more easily and spread quickly if they do.

Gusts up to 25 miles per hour blew across the San Fernando Valley Wednesday morning. The winds were expected to spread and intensify Thursday into Friday, with gusts likely to reach 70 m.p.h. in the mountains and 50 m.p.h. in the valleys.

“Friday is definitely going to bring the worst of it,” said Mike Wofford, a Weather Service meteorologist in Oxnard.

Strong winds were also expected to increase the wildfire threat in parts of the Sierra Nevada and its foothills, and in Lake County, a rural and agricultural region about 120 miles north of San Francisco. Red flag warnings were also issued across these areas.

Utility companies across the state said they may intentionally shut off power to some homes and businesses to reduce the risk that power lines knocked over by winds could send sparks flying.

Southern California Edison said it was considering cutting off power to about 250,000 customers; Pacific Gas and Electric may do the same to about 90,000 customers in Central and Northern California, including parts of the San Francisco Bay Area.

Late summer to early fall marks the start of windy season in Southern California. In September, the light ocean breeze that cools coastal areas often weakens just as winds blowing warm, dry air from the inland deserts can strengthen. “As the wind goes up and over the mountains, the air gets compressed and heats up,” Mr. Wofford said.

These often fierce winds that are funneled through canyons and into valleys are known as Santa Ana winds. Some of the worst fires in Los Angeles history exploded as these winds howled and gusts hurled embers across miles. When flames tore through the communities of Pacific Palisades and Altadena in January 2025, winds reached 100 m.ph. This week’s winds are not expected to be as extreme.

The winds this week will appear days after rain from a far-off tropical system dampened some of Southern California. San Diego recorded an inch of rain, while over three inches soaked the surrounding mountains. The areas most at risk for fire this week recorded much less rain, and the vegetation remains dry enough to ignite easily, forecasters said.

Though San Diego and Orange Counties are at lower fire risk thanks to the recent rain, the Santa Anas are expected to send strong winds there and east into the desert areas. A wind watch was in effect for much of those areas, with gusts over 70 m.p.h. possible.

California has experienced an unusually low amount of wildfires this year, with only 300,000 acres burning since Jan. 1, compared to the over one million acres that fires have usually burned by mid-October.

An earlier version of this article misstated the year that wildfires tore through Pacific Palisades and Altadena, Calif. It was January 2025, not 2024.

We acknowledge mistakes in our reporting with corrections. If you spot an error, please let us know at corrections@nytimes.com. Learn more. Amy Graff is a Times reporter covering weather, wildfires and earthquakes.