The 'Diablo winds' explain why the fires burning California's wine country became so destructive
California Highway Patrol/Golden Gate Division via Reuters
A series of fires in Northern California's wine country is shaping up to be one of the worst firestorms in state history. An estimated 20,000 people have fled the Sonoma and Napa valleys, as well as surrounding counties, as the fire races across fields and freeways.
More than 1,500 homes, businesses, and other structures have been destroyed. Schools and hospitals have been closed, and power outages are widespread. One person is dead.
The cause of the fires remained under investigation on Monday afternoon. But a weather phenomenon known as the "Diablo winds" is partly responsible for the widespread devastation.
It's peak wildfire season in California, and October is a notoriously challenging month for firefighters. Typically, sea breezes come off the Pacific Ocean and make landfall. In the fall, high pressure builds in the Great Basin - a huge swath of land that spans much of the western US - and causes wind to blow in an opposite direction, the Los Angeles Times reported.
Air descends from high elevations in Nevada and Utah down to sea level in Northern California, compressing and warming in the process. Winds - known as "Diablo winds" form.
In California's wine country, these especially dry winds arrived overnight, Jan Null, an adjunct professor of meteorology at San Jose State University, told the Los Angeles Times. They reached speeds of over 50 miles per hour, with gusts as high as 70 miles per hour.
Diablo winds probably didn't create the fires, but they did worsen the issue. Dry conditions, low humidity, and flame-fanning winds turned buildings and trees to tinder at a rapid rate.
"It's just about the worst case weather conditions to spread a wildfire quickly, given the fuel," UCLA climate scientist Daniel Swain told the Los Angeles Times.
Fires spread from ridge top to ridge top overnight, stretching over eight California counties.
You can see gusts of wind blowing through the vineyard at this Napa Valley winery.
California Governor Jerry Brown issued a state of emergency for Napa, Sonoma, and Yuba counties on Monday morning - a declaration that mobilizes the California National Guard.
"This is really serious. It's moving fast. The heat, the lack of humidity, and the winds are all driving a very dangerous situation and making it worse," the governor said at a morning news conference. "It's not under control by any means. But we're on it in the best way we know how."