A Santa Ana wind event is fueling a wildfire in Los Angeles that has destroyed homes and forced the evacuation of thousands of people. Here’s what to know about the winds.

How do the Santa Ana winds work?

The Santa Ana winds are the strong, dry and often warm winds that blow west from Nevada and Utah to Southern California.

The winds are most common in the colder months, when low- and high-pressure weather systems pepper across the mid-latitudes of the northern hemisphere, said Alex Hall, director of the Institute of the Environment and Sustainability at the University of California, Los Angeles. Sometimes, an area of high pressure can become locked in place over the arid, mountain-bound area known as the Great Basin, which covers much of Nevada, part of Utah and portions of other states, because of its unique geography.

To understand how the Santa Ana winds form, Mr. Hall said, imagine the Great Basin as “a big bowl,” topographically speaking, its sides lined with holes representing mounting passes. “If you have a lot of heavy, high pressure sitting there in the bowl, you’re going to be pushing air out through the holes,” he said.

When air rushes through the mountain passes — the bowl’s holes — the winds gain speed, moving toward the lower-pressure area of the Southern California coast.

The air of the Santa Ana winds is unusually dry because it originates in the desert environment of the Great Basin. And although it can begin cool for the same reason, it often warms as it becomes compressed while tumbling down the mountainside. (You might have noticed your bicycle tires warming when you fill them with air; the same principle is at work here, Mr. Hall said.)