https://phys.org/news/2018-07-local-key-role-megafires.html

The study team found that winds—both very localized winds related to topography and winds created by the searing heat of the flames—were the reason the fire suddenly ran 15 miles (24 kilometers) up a steep canyon one afternoon. Winds like these, sometimes only a few hundred yards (meters) across, often go undetected by weather stations that may be several miles away. In fact, for several days before the fire, nearby weather stations measured only weak winds.

"This brings into question several widely held and largely unquestioned assumptions, such as very large fires being caused by the accumulation of vegetation, persistent dry conditions, or requiring extreme conditions," said NCAR scientist Janice Coen, the lead author of the study. In the King Fire, she pointed out, "Small-scale winds and winds generated by the fire had a much greater impact on this fire, and potentially others like it, than any of the other factors."