Devil winds stoke hellish conditions
Low humidity helps feed flames ripping though wine country
A brutal combination of ferocious winds and near-record low humidity fueled the deadly wildfires scorching Northern California’s wine country and leaving a breathtaking trail of destruction.
Fierce northeast “Diablo” winds that circulated around a ridge of high pressure over the Great Basin blew through the region late Sunday, said Brian Mejia, a National Weather Service meteorologist in Monterey, Calif.
The winds allowed the runaway fires to jump fire lines and decimate entire neighborhoods, seemingly coming out of nowhere and sending residents running for their lives in the middle of the night — the worst possible time for such an emergency.
The toll Tuesday was staggering and could get worse from the more than a dozen blazes, officials warned: 15 people killed, more than 100 injured, more than 2,000 businesses and homes destroyed.
Through much of the summer,
winds blow into California from the ocean. But winds can switch in late September or early October to northeasterly from the bone-dry deserts of Nevada or Utah. This is a “classic wildland fire pattern in California, after five months of dry weather plus high pressure over the Great Basin, creating warm, dry winds,” said Jan Null of Golden Gate Weather Services.
In addition, as the winds howl down from the mountains toward coastal areas, they are compressed and become warmer. Then, as winds squeeze through canyons and valleys, they speed up, further fanning the flames.
Mejia said sustained winds were at least 40 mph in some spots; one gust registered as high as 79 mph in northern Sonoma County.
Earlier Sunday, the weather service had issued a “red flag” warning for the area, meaning conditions were ripe for the spread of wildfires.
Extremely low humidity — in the single digits, which is unusual for the area — also was a factor, Mejia said. Low humidity helps dry out vegetation, which makes it better fuel for fires.
A record wet winter of 2016-17 also allowed plenty of trees and brush to grow this spring, which became potent wildfire fuel.
The weather was similar to the conditions that led to the most destructive fires in California history: the October 1991 firestorm that struck the Oakland and Berkeley hills. The blaze killed 25 people and destroyed 2,900 structures.
October is always a difficult time in California for wildfires, but this year the wildfire eruptions seem extreme even to the most seasoned Californian.
The fires that roared across Northern California probably were not started by lightning, ac- cording to the weather service, which did not detect any strikes late Sunday or early Monday. That means the spark for the blazes probably was man-made, whether accidental or deliberate.
That isn’t surprising: About 84% of wildfires in the United States are started by people, according to a comprehensive study this year that was published in the Proceedings of the National Academy of Sciences.
The cause of the fires remained under investigation, said Barry Biermann, deputy incident commander for the California Department of Forestry and Fire Protection. But he wouldn’t say the rash of fires seemed suspicious.
“The wind were extremely erratic,” he said. “During those conditions of high winds, it doesn’t take much to start a fire.”
Hot, dry winds: “a classic wildland fire pattern in California.” Jan Null, Golden Gate Weather Services