When fires break out in Southern California, you often hear mention of the Santa Ana winds. These winds are famous: Raymond Chandler wrote in his novella Red Wind that the winds "come down through the mountain passes and curl your hair and make your nerves jump and your skin itch"; in her essay "Los Angeles Notebook," Joan Didion warned of the Santa Anas' "incendiary dryness," which she said "invariably means fire."
As the Hill and Woolsey Fires spread in Southern California, the Santa Anas are once again making headlines. But what exactly are they? And why are they such a hazard?
Most likely named for Orange County's Santa Ana Canyon, the winds (also known colloquially as "devil winds") blow from the Great Basin and Mojave Desert through Southern California's Transverse Ranges. As the winds funnel through mountain passes, they pick up speed. And as they descend to lower elevations, they heat up and lose moisture.
All in all, it's a recipe for strong, fast, and dry winds—which makes the parched chaparral of the region, especially in times of drought, extremely vulnerable to fire. Santa Ana winds can occur anytime from September to May, but they tend to be most dangerous in the fall, when summer droughts typically create the driest conditions, essentially turning the land into a tinderbox. And while the winds usually blow for just a few days on end, that's plenty of time for a tiny spark to spread into a vicious blaze.
Broadly known as katabatic winds, this phenomenon is not unique to the Los Angeles region. The Santa Barbara area, where the Thomas Fire burned more than 280,000 acres in 2017, experiences what are called "sundowner" winds because they tend to be most intense around sunset. Warm, dry winds descending from the Rockies into the Interior West of the United States and Canada are known as "Chinooks" (or "snow-eaters," because their heat can swiftly melt ice and snow).
As climate change makes a longer and harsher wildfire season, more and more people are seeing just how vulnerable their region—and their community—really is.
*Update—November 13, 2018: This post has been updated to reflect the manner by which Santa Ana winds lose moisture.