In Oregon, a New Climate Menace: Fires Raging Where They Don’t Usually Burn

Tim Brown, director of the Western Regional Climate Center at the Desert Research Institute in Reno, Nev., said the extreme warmth had caused vegetation to become exceptionally dry and to burn more readily. Temperature, humidity, wind and solar radiation combine to dry out brush and are the key elements for fire. “We call it evaporative demand,” he said. And in recent weeks, he added, “the west Cascades have been really dry from the evaporative demand.”

Those dry conditions were most likely exacerbated by climate change, according to Meg Krawchuk, a professor at Oregon State’s College of Forestry. And they had the effect of “teeing up the landscape” for a wildfire, she said.

The critical moment came Monday and Tuesday, when a windstorm carried hot air from the high desert in the eastern part of Oregon over the mountains, rapidly spreading the fires in the more populated western part of the state, according to Josh Clark, fire meteorologist at the Washington State Department of Natural Resources.

Those winds were the strongest the state has seen in at least 30 years, Mr. Clark said. And when they crossed the mountains, the winds raced down through river canyons, which compressed the air, warming it further and pushing it westward like a bellows.

As those fires raced west, they met unusually dry conditions, said Dr. Kolden, which in turn allowed the fires that were already burning to spread rapidly. “The fire’s able to move very quickly and just explode down these canyons,” she said.