What Are Santa Ana Winds?

A firefighting helicopter makes a water drop over the Easy Fire on Oct. 30, 2019 near Simi Valley, California. The National Weather Service issued a rare extreme red flag warning for Southern California for wind gusts that could exceed 80 mph (128 kph). David McNew/Getty Images

When the Santa Ana winds blow in Southern California, everyone takes notice. To many in the region — writers, singers, poets, just plain folk — they are a harbinger, mostly of no good.

To scientists who take a more dispassionate view, the Santa Anas are something else entirely: a perennial natural phenomenon whose future effects are now warped by a warming planet.

"Climate change has been projected to lengthen the dry season in California and other Mediterranean climate regimes, making vegetation more likely to remain dry into December," Alexander Gershunov, a climate scientist at the Scripps Institution of Oceanography at UC San Diego, told the university's news service early in 2019. "These changes together with the projected lessening of early season Santa Ana winds, suggest that Southern California's wildfire season could shift toward winter."

Longer, more dangerous dry seasons. Wildfires raging later in the year. Changes in the winds. It's potentially dramatic stuff. It might seem the stuff of Hollywood.

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The Science Behind Santa Ana Winds

Santa Ana winds are dry and warm winds from the Great Basin, an area that incorporates large parts of the states of Nevada and Utah. They start in the Basin's inland deserts, east and north of Southern California, and flow downward, taking a turn toward the Pacific Ocean.

Santa Anas are usually (but not always) late-year winds that form when the weather is cooler in the Great Basin; they don't begin in hot deserts. The winds, pushed toward Southern California by high pressure systems, actually start off as cool winds.

But as the winds head downslope, they get both warmer (air heats up as it descends) and drier. Robert Fovell, a Professor Emeritus at UCLA, explains in a FAQ on the UCLA site: "[I]f you take a piece of air located only a mile above your head, and brought it down to your feet, it would wind up 30 degrees Fahrenheit warmer than when it started," Fovell writes. "You don't need to change the altitude of air very much to alter its temperature significantly."

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How Do Santa Anas and Fire Mix?

Santa Anas have a reputation. The winds most often whip into Southern California during the driest part of the year, providing a metaphoric bit of gasoline to the already fire-ready tinder of the area. The winds exacerbated fires near the Ronald Reagan Presidential Library and Museum in Ventura County and the J. Paul Getty Museum in Los Angeles in late October 2019.

In December 2017, Santa Anas fueled the largest fire in Southern California history, the Thomas Fire, which burned 440 square miles in Ventura and Santa Barbara counties. According to research from Gershunov and others in a paper in the journal Geophysical Research Letters in 2016, Santa Anas have been the cause of a lot of grief:

Gershunov and his co-authors actually see, on average, a decrease in the frequency of Santa Anas, according to their paper. They predict the frequency of Santa Ana wind events will drop by an average of 18 percent by the end of the 21st century, largely because the Great Basin will have fewer days of the cold weather that is necessary to form the winds.

Though that may sound like good news, it's not. The Santa Anas still will have a busy period, as they do now, and it'll come in the peak of a later, possibly longer wildfire season. That peak will shift from October into November and the early winter months, which could, the authors write, provide "opportunities for wildfires to burn longer and bigger."

Strong Santa Ana winds blow hot embers from the Kincade Fire on Oct. 29, 2019 in Calistoga, California.

Justin Sullivan/Getty Images

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Getting Worked Up Over Winds

As a weather phenomenon that is unique to Southern California, Santa Anas have long been associated with a certain feel. Novelist Raymond Chandler, a master of the detective story ("The Big Sleep," "Farewell My Lovely") and a longtime Southern California resident (he's buried in San Diego), described a windy Santa Ana night in his 1938 short story, "Red Wind":

Santa Anas can sweep out impurities in the air, provide welcome warmth and offer bright blue skies and stunning sunsets in the winter. The Beach Boys took this more upbeat look at the winds in their song "Santa Ana Winds:" Fill my sails/Oh desert wind/And hold the waves high for me/Then I will come/And test my skill/Where the Santa Ana winds blow free.

Still, to a large segment of residents in the area, the Santa Anas have an ominous feel to them. The Los Angeles-based punk band Bad Religion fell more into that Chandlerian view. The band's 2004 song, Los Angeles is Burning, puts it pretty succinctly:

Essayist Joan Didion is frequently cited when it comes to Santa Ana popular culture references. In her essay "The Santa Ana," published as part of "Los Angeles Notebook" in "Slouching Towards Bethlehem," Didion writes:

Whatever lies in store for the Santa Anas and all they wreak is still a matter for the future. But for now, the warm, dry winds continue to blow. The citizens of Southern California can feel it.