SIMI VALLEY, Calif. — Hurricane-force gusts and single-digit humidity levels combined Wednesday to spark a number of fires across Southern California, including one here that threatened the Ronald Reagan Presidential Library for several morning hours.

Dire weather predictions and an “extreme red flag warning” across much of the state’s south had prompted firefighters to take up positions before several of the blazes started, giving them a jump on knocking them down. The blaze here, known as the Easy Fire, burned more than 1,600 acres very quickly but, by early afternoon, had burned just one home.

Ventura County firefighters had several strike teams in place at the Reagan Library, and intensive aerial attacks from helicopters and a DC-10 tanker kept the flames off the hilltop where the building sits. The library’s safety was far from certain, though, during a morning when conditions conspired against hundreds of firefighters on the ground.

“It was about the worst time it could happen,” Ventura County Police Chief Mark Lorenzen told reporters at a noon briefing. “And, unfortunately, these winds are going to continue for at least the next 24 hours.”

The Easy Fire was the largest one that broke out Wednesday, but throughout the day, brush fires popped up along busy highways on the outskirts of Los Angeles, stoking fears that fires could start — and spread — quickly and with little warning to heavily populated areas along the California coast.

The wind was so fierce in Riverside County to the southeast, where the Hill Fire threatened mobile home parks and senior care hospitals, that it blew over several 18-wheel trucks navigating traffic-clogged roads. Eucalyptus bent almost parallel to some highways as debris was tossed through the air. Public officials in high-wind areas warned drivers to stay home.

The routine has become familiarly grim to thousands of Californians after weeks of wildfires from north of San Francisco to south of Los Angeles. Schools closed in many Los Angeles suburbs, and employees left work early to take care of children and check on homes as fires advanced and smoke streamed across the sky.

Throughout the day, people checked the boundaries of mandatory evacuation maps on cellphones. Nearly 20 million state residents are living within high-risk fire areas, which have grown in size as the state’s climate turns to one of extremes.

Fire crews were still trying to contain the Getty Fire, on the western edge of Los Angeles, which was sparked Monday when a tree branch fell on power lines in Los Angeles County. The northeast Santa Ana winds were far calmer in the city Wednesday than on its outskirts to the north and south.

So far, the Getty Fire has torched about 745 acres and forced the evacuation of more than 7,000 homes. At least 12 homes have been destroyed.

In the north, the Kincade Fire grew to 76,825 acres in Sonoma County, threatening some of the same wine-country towns and cities that burned in the fall of 2017 to become the largest so far this year. By Wednesday evening, the fire had been more than 45 percent contained.

At least 266 buildings have been destroyed, 133 of them homes. Firefighters there received some relief from the weather as the predicted 70 mph winds, known as Diablos, did not whip up to that strength. The National Weather Service canceled its wind advisory for the North Bay Area before dawn. But the number of people affected by mandatory evacuation orders continues to dwindle, and Sonoma County officials said late Wednesday that residents would be able to return to a number of zones.

The weather concerns over the next two days are focused on Southern California, where the National Weather Service took the unprecedented step of issuing an “extreme red flag warning” to communicate the severity of the event now underway.

As of 6 a.m., just before the Easy Fire broke out, peak wind gusts in Los Angeles and Ventura counties had reached 65 mph. Gusts increased through the early afternoon.

“The fire outflanked us very quickly this morning,” said Chad Cook, the incident commander with the Ventura County Fire Department.

Cook said the heavy winds and resulting turbulence shut down air operations off and on throughout the morning. But those pauses were brief. The sight of helicopters dropping water, collected from nearby reservoirs, and tankers dumping flame retardant, painting the tan hills fluorescent, was near constant.

“It’s been give and take, off and on,” Cook said.

One of the key factors that forecasters use in predicting the strength of offshore wind events in California is the pressure gradient between coastal portions of the state and areas far inland. The greater the pressure difference, the stronger the winds will be. Forecasters and residents say the winds have been the strongest in more than a decade.

The evacuations related to the Easy Fire in Los Angeles affected about 30,000 people. Overnight, the Ventura County Sheriff’s Department had deployed 81 officers to areas at most risk of fire, giving them an early start on the evacuations that Sheriff Bill Ayub called “fairly seamless.”

At one point early Wednesday, the fire burned along ridgelines and in the canyons around the Reagan Library, the repository for the late president’s papers, the aircraft that served as his Air Force One, and other historical materials. Ronald and Nancy Reagan are buried there.

“We made some successful stands up there and managed to protect the buildings and the infrastructure around it,” Cook said.

On its website, the library posted an advisory that it was closed for the day. The message added: “Thank you to all the first responders working so hard to protect our area.”

Mettler and Freedman reported from Washington. Lateshia Beachum, Derek Hawkins, Marisa Iati and Jason Samenow in Washington contributed to this report.

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