The 'Diablo winds' explain why the fires burning California's wine country became so destructive


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. Ten people have died.

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.

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Canyon Fire 2 in Orange County, California
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Canyon Fire 2 in Orange County, California
A woman evacuates horses as strong Santa Ana winds blow fire and smoke from the Canyon 2 Fire toward them on October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A police car blocks the 241 freeway as smoke from the Canyon 2 Fire covers the freeway near Orange, California, October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A helicopter drops water near homes at the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
People watch water-dropping helicopters amidst smoke from the Canyon Fire 2, October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A DC-10 aircraft drops fire retardant on a wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
Firemen put out a fire in a house in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Firemen put out a fire from a house in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Burning embers remain from a demolished home in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
A fireman puts out a fire from homes in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Burning embers remain from a demolished home in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Firemen put out a fire from a house in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Firemen put out a fire from a house in the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area destroying homes, prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Firemen survey the damage to homes at the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Firemen put out a fire at the Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
A fireman puts out a fire in a home at an Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
A fireman puts out a fire from a home at an Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
A fireman puts out a fire in a home at an Anaheim Hills neighborhood in Anaheim, California on October 9, 2017, after a fire spread quickly through the area prompting mandatory evacuations and freeway closures. / AFP PHOTO / FREDERIC J. BROWN (Photo credit should read FREDERIC J. BROWN/AFP/Getty Images)
Trees sway in the Santa Ana Winds as a smoke rises from the Canyon Fire 2, October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
Flames from the Canyon 2 Fire burn tree and brush along the 241 freeway near Orange, California, October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
Traffic jams up as people flee from Santa Ana winds blowing fire and smoke toward them from the Canyon 2 fire on October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A man evacuates horses as strong Santa Ana winds blow fire and smoke from the Canyon 2 Fire toward them on October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A man leaving Santiago Canyon College in Orange, California looks back as strong Santa Ana winds blow fire and smoke toward the college on October 9, 2017,as the Canyon Fire 2 sweeps through the area after breaking out this morning. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A police car blocks the 241 freeway as smoke from the Canyon 2 Fire covers the freeway near Orange, California, October 9, 2017 in Orange, California. / AFP PHOTO / Robyn Beck (Photo credit should read ROBYN BECK/AFP/Getty Images)
A firefighter works to put out hot spots on a fast moving wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
A firefighter works to put out hot spots on a fast moving wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
A firefighting helicopter flies in to make a water drop on a wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
Residents use their phones to record firefighters fighting a wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
Firefighters work to put out hot spots on a fast moving wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
A firefighter battles a fast moving wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
Firefighters work to put out hot spots on a fast moving wind driven wildfire in Orange, California, U.S., October 9, 2017. REUTERS/Mike Blake
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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."

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SEE ALSO: This map shows the devastating impact of fires ravaging parts of California's wine country

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