Powerful, hot and dry winds like those that have fanned the deadly wildfires now raging in California are a common occurrence in the state, a result of regional atmospheric patterns that develop in the fall.
The impact of climate change on the winds is uncertain, although some scientists think that global warming may at least be making the winds drier. “That is a pretty key parameter for fire risk,” said Alex Hall, a climate researcher at the University of California, Los Angeles.
The winds, known as Diablo winds in Northern California and Santa Ana winds further south, have their origin in the high desert of the Great Basin of Nevada and parts of Utah. High-pressure air that builds over that region flows toward lower-pressure air over California and the coast.
Along the way the air descends to lower elevations, which causes it to compress and become hotter and drier. The air picks up speed as it descends and funnels through canyons or across peaks that are lower than their neighbors.
“The wind is seeking the path of least resistance to lower pressure,” Dr. Hall said. “That tends to be where there are gaps in the topography.”
The result is hot, dry winds with speeds that can exceed 70 miles per hour. In the wildfires that have devastated parts of Northern California’s wine country since Sunday night, the highest gusts were recorded in Sonoma County, at 79 m.p.h.
The state got some respite from the winds on Tuesday, but they were expected to pick up again Wednesday and Thursday. Scientists said such variation is typical, as there is natural variability to large-scale climate patterns like high-pressure systems. If the high pressure over the Great Basin moves eastward, for example, the air will be less likely to flow westward, and that may allow cooler, gentler winds to move into California from offshore.