What are they and how do they impact the LA wildfires? : NPR

Smoke from the Palisades Fire can be seen from Point Dume as it burns homes along the Pacific Coast Highway during a fierce storm on Wednesday in Malibu, California. Spurred by fierce Santa Ana winds, the Palisades Fire has burned thousands of acres of land, while a second major blaze continues to burn near Eaton Canyon in Altadena.

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The fierce and fast-spreading fires that have cut a path of destruction through the Los Angeles suburbs, leaving at least two people dead, are being driven by the region’s strong Santa Ana winds, whose gusts in some cases are the exceed the strength of a hurricane.

The two largest fires — the Palisades and Eaton fires — have each burned more than 10,000 acres and led to the forced evacuation of nearly 70,000 people as of Wednesday. Another 58,000 people were warned to prepare to leave at short notice.

Although the Santa Anas are a routine Because the winds are a part of everyday life for people in Southern California, they will be particularly fierce and destructive this time, experts say.

Strong winds are expected to make it difficult or impossible for firefighters to contain the fires until conditions improve. However, the National Weather Service is currently warning of sustained winds of up to 40 miles per hour in the region and gusts of up to 80 miles per hour in the area of ​​the wildfires.

Mike Wofford, senior forecaster at the National Weather Service office in Oxnard, California, says the Santa Ana winds are most common in the cooler months of September through May. They are caused by high pressure over the desert in the southwestern United States pushing through the mountain passages in Southern California into an area of ​​lower pressure off the Pacific coast.

“The high pressure developing over this region, coupled with the lower pressure down over Southern California, creates this strong flow of air coming from Nevada and hitting our coastal range, the San Gabriel Mountains, and out into the Inland Empire area. ” says Wofford.

The main feature is that the winds are so-called katabatic winds, meaning they flow downhill, says Mingfang Ting, a professor at Columbia University’s Climate School.

As the air mass loses altitude, it compresses and warms – by about 10 degrees Celsius per kilometer (18 degrees Fahrenheit per 0.6 miles). It’s a “very effective way to warm the air,” she says.

“As the air warms, its humidity also decreases,” she says. When crossing narrow mountain passes, it accelerates in the same way that air flowing through a tunnel or the wind between buildings is stronger.

Typically that makes for warm, dry Santa Anas that can reach speeds of 40-60 mph, with gusts over 70 mph.

➡️ The Santa Ana Winds: A Cultural and Destructive Force in Southern California

But “that’s not typical,” Wofford says. This time, the Santa Anas are associated with “very strong winds in the upper atmosphere.” Not only did they funnel through the mountains, but they also rose up and over the mountains and then sank down into the basin area,” he says.

The result is wind gusts of up to 100 miles per hour in some locations, he says, adding that due to the current drought, “everything is prepared and ready for wildfires.”

“Obviously we have tons of cars in the area. If one breaks down, overheats and someone stops in an area where there is dry brush, that can be the deciding factor,” he says.

Park Williams, professor of geography and head of the HyFiVeS (Hydroclimate, Fire, Vegetation and Society) research group at UCLA, describes the current scenario as a “highly unlikely sequence of extreme climate and weather events over the past two years.”

It’s not just the dry weather this year, he says, but “from the winter of 2023 to the spring of 2024, the Los Angeles area experienced an exceptionally wet climate, resulting in the growth of an extraordinary amount of new vegetation biomass in the surrounding hills and mountains.” . “the city.”

What role could climate change play? As NPR previously reported, a hotter atmosphere caused by climate change could lead to rapid spread of wildfires.

As for the impact on the frequency and intensity of the Santa Ana winds, Ting is cautious. “I’m not sure,” she says. “I think in this case the drought in the region is more important if you want to say something about the role that global climate change plays.”

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