(Bloomberg) -- An hour is all the time needed to turn a few twigs and grass into fuel for a fire.

Blazes like the California ones that killed more than 40 people, caused billions of dollars in damages and charred hundreds of thousands of acres last year can spark quickly as dry and windy conditions wring the water out of plants, brush and dead branches, said Janice Coen, project scientist at the National Center for Atmospheric Research in Boulder, Colorado.

“It is not so much that the season is dry but the last hour has been dry and perhaps windy,” Coen said. Though once a wildfire gets going, it may no longer be at the mercy of the weather but start affecting it, she said.

California’s King Fire, which burned almost 98,000 acres (40,000 hectares) in September and October 2014, entered a canyon, and the combination of the topography and the fire-created weather caused it to burst across more than 15 miles (25 kilometers) in a single day, she said. In the Klamathon Fire, currently burning through 36,500 acres in Siskiyou County, California, winds blew in from all directions, causing the fire to spread rapidly.

“Some people misattribute why some large fires become large,” Coen said.

To contact the reporter on this story: Brian K. Sullivan in Boston at bsullivan10@bloomberg.net

To contact the editors responsible for this story: Lynn Doan at ldoan6@bloomberg.net, Margot Habiby, Joe Ryan

©2018 Bloomberg L.P.