Every year between fall and spring, Southern Californians experience gusts of dry wind that can cause runny noses or watery eyes — and sometimes powerful enough to halt traffic or topple trees.
The Santa Ana winds, as they’re known, are a naturally occurring phenomenon made possible by the geography in the western U.S. They become particularly dangerous when combined with other climate conditions such as drought, which increases the risk of wildfires like the ones currently raging in the Los Angeles area.
This year’s gusts — at times approaching hurricane strength — were more widespread than usual. Coupled with an exceptionally dry winter, they created ideal conditions for blazes to spread. Around 29,000 acres have been scorched by the Palisades and Eaton fires that began Tuesday, as well as three smaller fires that started Wednesday.
“The low-moisture content in the vegetation that we get in these extreme dry periods leads to these highly, highly vulnerable conditions,” said Mark Gold, director of water scarcity solutions at the Natural Resources Defense Council. “And boy, when a big Santa Ana hits, that’s when the nightmare for our firefighters really kicks in.”
The Santa Ana winds form in a western area of the country known as the Great Basin, which includes Nevada and part of Utah. The basin sits at a higher elevation than Southern California.
In cooler months — typically September to May — cold air in the basin is forced downhill and westward toward low-pressure areas along the Southern California coast. As the air travels, it’s squeezed through mountain passes and canyons, picking up speed and becoming hotter and drier along the way.
By the time they reach Southern California, the winds can move at a speed of 40 mph, with gusts that are even stronger.
Robert Fovell, a professor of atmospheric and environmental sciences at the University of Albany, said the windiest areas tend to be Ventura County in Los Angeles and Santa Ana in Orange County, from which the winds derive their name.
But this year, he said, the winds were able to travel over the San Gabriel Mountains down to Pasadena and Altadena, where the Eaton Fire is located.
“It surmounted the San Gabriel Mountains, and it formed what is called a downslope windstorm,” he said. “That targeted the strongest winds for the foothills around Eaton Canyon.”
Tripti Bhattacharya, an associate professor of earth and environmental sciences at Syracuse University, said her models don’t predict that Santa Ana winds will get worse this century. But they do predict more overlap between the winds and the fire season, she said, creating more opportunities for devastating blazes like the ones seen this week.
“In California, we used to think of fire as a late-summer occurrence, but now fire season is extending into January,” Bhattacharya said. “So that fire season is more likely to coincide with Santa Ana winds in the future.”
