Photo: AP

The always prescient Joan Didion described the Santa Ana winds—currently the driving force behind the devastating California wildfires—and their relationship to Los Angeles this way:

“Los Angeles weather is the weather of catastrophe, of apocalypse, and, just as the reliably long and bitter winters of New England determine the way life is lived there, so the violence and the unpredictability of the Santa Ana affect the entire quality of life in Los Angeles, accentuate its impermanence, its unreliability. The wind shows us how close to the edge we are.”

Now those winds have pushed the city and greater metro area over the edge, turning the landscape into a fiery hellscape. Winds gusting up to hurricane force have created some of the most dangerous fire conditions in 30 years according to Los Angeles’ fire chief.

This Santa Ana wind event is exceptional, but the winds themselves are a regular feature of life in Southern California from fall through spring. December and January are usually the peak of the wind season, which is usually driven by an atmospheric tug of war between weather systems over the Great Basin—the region that sits between the Sierras and the Rockies—and the Pacific Ocean, with California unfortunately caught in the middle.

The whole pattern starts in the desert when high pressure sets up over the Great Basin. That, by the way, is exactly what happened earlier this week as a monster ridge built over the region.

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Winds circle the area of high pressure clockwise in what scientists call an anticyclonic flow. That air can eventually start to slip away from the high pressure, especially if there’s a low pressure system over the Pacific, and flow over the Sierra Nevada mountains and toward the coast.

Known as a katabatic wind, this type of wind can be found in various spots all around the world. In Northern California, they’re called Diablo Winds. In Alberta, they’re Chinooks. In Austria, they’re dubbed foehn winds. I could go on but you get the drift.

A pressure anomaly forecast through early Monday morning. Red indicates anomalously high pressure. Image: Tropical Tidbits

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Anyways, as the Santa Ana winds push over the mountains and move downslope into the valleys, the air compresses. That causes it to heat up and dry out, which by extension dries out any vegetation in the way, priming it to explode if there’s a spark.

Canyons funnel the winds even more, causing them to accelerate further, which is how you end up with winds gusting 50 mph or higher by the time they reach Southern California.

And that’s why the region is in such dire straits right now. Months of dry weather parched the landscape, which was further dried out by the Santa Anas. When sparks lit the current swath of fires, it ensured the landscape would quickly ignite.

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With an exceptionally strong ridge of high pressure camped over the Great Basin, there’s a perpetual source to send winds gusting to the lowlands and ensure fire conditions continue to be threatening. The danger will continue into at least next week. More than 20 million people live in areas facing extreme or critical fire weather through Sunday, before the areas at risk shrink slightly on Monday.

Winds on Wednesday night in the Santa Monica Mountains peaked at 85 mph, the equivalent of a robust Category 1 hurricane. The Los Angeles Times reports that winds weren’t as bad in the valleys though, which allowed firefighter to start to contains the Thomas, Creek and Rye fires, the three biggest fires currently afflicting the region.

The Thomas Fire, which has burned nearly 100,000 acres, is only 5 percent contained. The Creek and Rye fires were 10 and 15 percent contained respectively as of Thursday morning. Despite the good news, they still face a major uphill battle to get them totally under control. And days of heat, fire and smoke are likely to continue until then.

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For fire-weary Angelenos, that’s why pulp fiction writer Raymond Chandler’s famous description of the winds probably still rings true:

“There was a desert wind blowing that night. It was one of those hot dry Santa Anas that come down through the mountain passes and curl your hair and make your nerves jump and your skin itch. On nights like that every booze party ends in a fight. Meek little wives feel the edge of the carving knife and study their husbands’ necks. Anything can happen.”