ARI SHAPIRO, HOST:
As those massive wildfires burn through Southern California, you'll likely hear a lot about the effect of what's called the Santa Ana winds. Many people, especially on the West Coast, are probably familiar with them.
AILSA CHANG, HOST:
Well, I know I definitely am. But you out there may be asking, what are Santa Ana winds exactly? Well, in this case, high pressure builds over the Nevada and Utah deserts and blows west into the San Gabriel Mountains in coastal California. And then...
MINFANG TING: The key characteristic of those winds are it's downslope. It blows from the top of the mountain coming down, and experience increasing pressure, or what we call compression, right? And that is causing the air to warm up very quickly.
CHANG: That's Mingfang Ting, a professor at Columbia University's climate school.
TING: The rate of warming is about 10 degrees per kilometer of dropping the air altitude. So, you know, imagine if the mountain is 2 kilometers high. When it blows from the top of the mountain to the bottom, it'll increase temperature by 20 degrees Celsius, which is like, you know, 30-some degrees. Very high, very fast, a very effective way of warming up the air.
SHAPIRO: Then that compressed hot wind blows down to the valley below, pushing between the mountain ranges the way wind picks up in city blocks with tall buildings. Here's Mike Wofford from the National Weather Service.
MIKE WOFFORD: If it wasn't for the mountain range there, this would never happen. All the winds would just keep going straight across. And those winds descend down, and when they descend down, they accelerate. So they're actually even stronger as they reach the surface than they were higher up.
CHANG: The Santa Ana winds are a pretty routine part of life here in Southern California in the colder months. But Wofford says this year, the winds have been especially bad.
WOFFORD: This was not a typical Santa Ana wind event. It was a Santa Ana wind event but kind of on steroids.
SHAPIRO: He says it's also unique that these winds have covered so much ground.
WOFFORD: In typical Santa Ana events, like I said, it's a little more spotty. It's a much more confined area. But when we get this kind of event, it's much more widespread, and it covers places like Pasadena, which typically in a normal Santa Ana wouldn't get any wind - like literally zero wind. Even in other areas, it's quite a bit stronger and more widespread. So it's, you know, more destructive, more impactful in many areas than a typical Santa Ana is.
CHANG: Wofford says the strongest of this Santa Ana wind event is now behind us, thankfully, but that doesn't mean it's over.
WOFFORD: It's going to be a battle. And if we didn't already have existing fires, it wouldn't necessarily be a big deal. But because we do, that's going to be an issue that's going to be ongoing for the next weeks.
SHAPIRO: Santa Anas generally blow through Southern California into the spring, though. So if dry conditions persist, so, too, does the danger of wildfire. Transcript provided by NPR, Copyright NPR.
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