Smoke was heaviest southeast of Los Angeles and widespread across the rest of Southern California. Data from air sensors suggested that the air quality was diminished in several places around the Los Angeles area. Air quality was also poor in the Northwest, including in Oregon and Idaho, where dozens more wildfires were burning.

"That one-two punch, that sequence, means you grow all this extra potential fuel for fires and then you dry it out to extreme levels," said Daniel Swain, a UCLA climate scientist whose research suggests California's rising temperatures create wetter winters.

A blaze threatened thousands of home and commercial structures as it burned along the edge of the San Bernardino National Forest, about 65 miles east of Los Angeles.