What Are Diablo Winds?

CC BY 2.0. California Highway Patrol

The winds that fan catastrophic Northern California fires are borne out of a complicated mash-up of meteorology, physics, geography, and topography.

In 2017, Sonoma and Napa counties were thick in the midst of some of California’s worst fires ever. Those in the Golden State know to expect massive fires in the wilderness, but that particular firestorm broke normal convention and devoured whole neighborhoods at a terrifying rate. It’s as if a giant flamethrower had been aimed at blocks and blocks of tidy homes, leaving little more than charred rubble punctuated by the eerie pillars of fireplace chimneys.

There were many stories of people waking up to the smell of smoke and seeing flames in the distance, only to see those flames charging towards them at a furious rate. So rapacious were those fires that many reported fleeing their homes in only robes and slippers, leaving everything from their wallets to their pets in order to get out in time.

To anyone who hasn’t experienced California’s surreal hot winds – the Santa Anas in the south and the Diablo Winds (AKA the Diablos or El Diablo) in the north – it may be hard to fathom how a fire could devour a football-field sized parcel of land in three seconds. But if you know these winds, it is all too sadly comprehensible.

Basically, imagine a gigantic blow dryer on its hottest setting, being turned up to high in random gusts – and when I say high, I mean hurricane force. This wind is hot and dry and strong; and if it weren’t for its diabolical relationship with wildfires, it might be kind of a sexy thing. But no, at this point it’s just dreadful.

The winds originate in the Great Basin, which you can see in the map below.

great basin map

Wikimedia Commons/CC BY 2.0

Dr. Marshall Shepherd, a leading international expert in weather and climate, describes it like this:

If an area of high pressure is situated over that region [the great Basin], winds blow from the central Great Basin toward the Pacific coast. In the northern hemisphere, winds flow clockwise around high pressure and that creates the aforementioned flow.
With such a flow regime, the winds are forced over and descend down the elevated terrain and mountains on the western edge of the basin and in California. Since Mt. Diablo is in the region east of the Bay Area, these particular winds get the name Diablo Winds. Here is where the physics comes in. As these winds descend, they are compressed and warmed. These winds can reach tropical storm (39 mph) to hurricane force (74 mph).

(He then goes into the nitty gritty of adiabatic compression and the First Law of Thermodynamics – and much, much more, all of which you can read over at Forbes.)

For 2017's particular perfect storm, fuels were at or approaching an all-time record for dryness, according to analyses by land management agencies. The weather service described an abundance of grasses produced by “record winter rains combined with heavier vegetation stressed by years of extreme drought and disease.” Mix that with a bit of wind from the devil and the result is a burned barren landscape, ravaged and grim.

In iconic Californian writer Raymond Chandler's short story, "Red Wind," the state's oven-hot winds are such a prominent component of the narrative they practically become a character on their own. The story opens with a telling description:

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.

And the same goes for the red wind's devilish relative in the north. Anything can happen when the Diablo Wind starts fanning the mayhem.