Two massive wildfires burning in California have now become the state's deadliest and most destructive. In Northern California, the Camp Fire near Chico decimated the town of Paradise and killed 29 people as of November 12, 2018. In Southern California, the Woolsey Fire started near Simi Valley northwest of Los Angeles, and has torched hundreds of homes in Malibu and other communities.

The National Weather Service says that a combination of high temperatures, low humidity, and gusty Santa Ana winds have created perfect conditions for cataclysmic fires.

What are these Santa Ana winds and why do they help create fire conditions?

Santa Anas are dry, warm (often hot) winds that blow westward through Southern California toward the coast. They're usually seasonal, and typically occur between October and March and peak in December. They originate when high pressure systems form over the high-elevation deserts of the Great Basin between the Sierra Nevadas and the Rocky Mountains. Air from the system flows clockwise, so winds on the southern side of the system push west towards the Pacific Ocean.

The winds pass over the mountains between coastal California and the inland deserts. As they flow downslope, the air gets compressed and rises in temperature at a rate of almost 29 degrees per mile of descent. While air's temperature rises, its relative humidity drops, commonly to less than 20 percent and sometimes to even less than 10 percent. The winds also increase dramatically in speed when they're forced through narrow mountain passes and canyons.

By the time the winds hit the coastal areas, they're very dry, warm, and moving fast. This is what makes them problematic. They dry out vegetation, making it better fuel for a fire—and once a fire starts, the winds fan the flames and help spread them.

WHAT'S IN A NAME?

So, why are the winds called "Santa Ana winds"?

"While the origin and cause of the Santa Ana winds are not in dispute," writes Robert Fovell, currently a professor of atmospheric and environmental sciences at SUNY Albany, "the origin of the name is."

One fairly popular explanation is that the name comes from a Native American word, santana, which means "devil wind" and was corrupted into Santa Ana. But according to Fovell, the Los Angeles Times, and other sources, no one has found any words similar to santana with that definition in any of the native languages of the area.

Another explanation is that the winds were named for Mexican politician and general Antonio López de Santa Anna, possibly in reference to dust storms kicked up by the cavalry he commanded. Santa Anna never operated in southern California, though, and spelled his name with two n's. The Oxford English Dictionary dismisses this etymology as having no foundation.

In the early 1930s, an article in the United States Naval Institute Proceedings suggested that the name might have originated with early Spanish explorers, who had a "custom of naming places and events for the saint's day on which they happened or were discovered." In this case, they might have noted the winds on St. Anne's day and named them for her. This also seems unlikely to historians, though, because a few Santa Ana winds, experienced for the first time, probably wouldn't have warranted naming—and the winds aren't recorded with any name until much later, anyway. St. Anne's feast day is also July 26, when a Santa Ana wind is unlikely.

The most common and accepted etymology, says Fovell, is that the winds' name simply derives from the Santa Ana canyon in Orange County.

This article was originally published in 2014 and has been updated.