Wildfires continue to spread in Southern California amid strong land-to-sea winds and bone-dry air, forcing nearly 100,000 people to quickly evacuate from two growing blazes in Orange County. Red flag warnings blanket the entire state for “critical” fire conditions, as relative humidity stays in the single digits to low teens and winds gust to hurricane-force in some higher elevations.

Nearly a million Californians were without power on Tuesday morning because of deliberate power cuts that utilities, mainly Pacific Gas & Electric Corp., made to reduce the risk of sparking a major blaze. Some outages were also caused by wind knocking down trees and power lines.

The two main fires prompting evacuations are the Silverado Fire in Irvine and the Blue Ridge Fire in Yorba Linda and the Chino Hills.

Two young firefighters were critically injured Monday while fighting the Silverado Fire, according to the Orange County Fire Authority. That blaze grew from just a few acres Monday to 11,200 acres on Tuesday morning, with 5 percent of it contained. According to the fire authority, no structures have been lost to the blaze, even though it has burned close to heavily populated areas.

The Blue Ridge Fire grew significantly Tuesday and was at 15,200 acres on Tuesday at midday, with 10 homes damaged in Yorba Linda, the fire authority said.

Winds are still expected to cause rapid fire spread and extreme fire behavior, though they’re not as strong as they were on Monday, when a gust to 96 mph was measured in Los Angeles County and gusts up to 88 mph buffeted areas near Fremont Canyon. Ontario Airport saw a gust to 70 mph, and had to shut down due to the severe crosswinds.

This week’s extreme winds brought the most dangerous conditions the Los Angeles area has seen since October 2019, National Weather Service forecasters said. To raise awareness about the threat, the Weather Service office in Los Angeles called Monday’s fire weather a “Particularly Dangerous Situation” (PDS) — a label it reserves for rare events that combine wind gusts greater than 60 mph with single-digit humidity and highly flammable vegetation.

The PDS designation replaces the “Extreme Red Flag” warning that the Los Angeles office issued during a severe Santa Ana event last year.

The agency is reviewing red flag warnings because there is concern that they may not be an effective way to communicate high fire danger.

The roaring, dry winds during the past two days might not have presented a high-risk scenario if California had received a meaningful rainstorm in October. But the state is bone dry — most areas have seen little to no wetting rainfall for months.

Much of Northern California remains in severe to extreme drought, and that drought has been exacerbated by record heat. The months of August and September ranked as the state’s hottest since records began in 1895.

A heat wave and unusual barrage of lightning in Northern California sparked a slew of devastatingly large blazes in August. Another heat wave, this time even more severe, led to widespread fires again in September. On Sept. 6 Los Angeles County set a record for its highest temperature on record, when a station hit 121 degrees.

Recent studies have shown that warming and drying fall seasons are amplifying the fire threat, as the number of extreme fire weather days increases and very dry conditions extend later into the year. This trend is the result in part of human-caused climate change and has also been seen in other parts of the world.

One study, for example, found that climate change has doubled the days during the fall with extreme wildfire conditions in parts of California since the 1980s.

Since Southern California typically gets most of its land-to-sea wind events, known as Santa Ana winds, during October and November, this shift in timing means the driest time of year increasingly overlaps with the windiest.

A ‘concerning’ fall for Southern California

California is in the midst of its worst wildfire season on record, with more than 4.1 million acres burned, which is more than double the acreage burned in the previous record-breaking year. In addition, at least 9,200 structures have been destroyed and 31 people killed. A staggering five of the top six largest fires on record in the state have occurred this season, including the largest, the August Complex.

Although it hasn’t burned to the degree the drought-stricken North has, Southern California still faces a risky autumn.

“Santa Ana season has just begun, and, as long as it’s not raining, we’re in a bad situation,” said Alex Tardy, warning coordination meteorologist for the Weather Service’s San Diego office.

“What’s so concerning this fall is that the fuel is drier than it’s been in the last five years and, in some areas, drier than we’ve ever seen,” he said, referring to vegetation and trees.

Much of Southern California saw ample rainfall this winter and spring, so how did it get so dry? According to Tardy, 14 distinct heat waves have scorched the region since the start of the summer, most of them between July and September. Even the coast, which saw less intense heat than inland areas, recorded its third-hottest July through September period since 1895. There has also been long-lasting warmth, too, with L.A. set to tie its longest streak with daily highs of 70 degrees or above, at 190 days.

After the winds subside Tuesday night, very dry air will remain in place, and a warming trend begins midweek, with no rain yet in the forecast. And this year, La Niña’s cold waters along the equatorial eastern Pacific Ocean favor a drier than average winter in Southern California.

“We need a lot of rain — a good soaker or two — to help us because of the record dry vegetation,” Tardy said. “We’ve got a long way to go before this fire weather season is under control.”

Diana Leonard is a science writer covering natural hazards, especially wildfires. She holds master’s and doctorate degrees in geography from the University of California at Berkeley, where she studied physical geography and climate change.