Fires burning hundreds of miles away have blanketed Bay Area coastal counties in a smoky haze.
"It reminds me of San Bernardino," Ukiah attorney Mark Ranft said of the grayish-brown skies.
The primary culprits are fires burning in Oregon, where crews are battling six major fires.
Lightning late last week touched off dozens of fires in southwest Oregon near Glendale. Most of the small ones were contained, and some merged into larger fires that make up a fire known as the Douglas Complex.
Those fires had burned 21,000 acres, or nearly 33 square miles, and were just 2 percent contained as of Monday afternoon. More than 100 houses have been evacuated and others are on evacuation alert.
The Bay Area Air Quality Management District warned this week that air quality would remain in the unhealthy range throughout the area for several days as the smoke drifts south.
Health officials are recommending that people who have health conditions that make them sensitive to smoke limit their outdoor exposure. Persons with severe heart or lung problems should consult their doctors, the Air Quality Management District advised.
The air was expected to clear by Tuesday but did not; the smoke appears to be trapped in low-lying areas, said Bob Ruehl, observing program leader with the National Weather Service in Eureka.
Smoke also may be coming from Fresno County, where firefighters are battling flames in the Sequoia National Forest, he said.
"The smoke was going into the Central Valley and up. I wouldn't be surprised if you got some of that," Ruehl said.
As of Tuesday afternoon, no fires were burning in either Lake or Mendocino counties, said Cal Fire spokeswoman Julie Cooley.
Lake County officials are expecting their famously clean air to begin returning to normal Thursday.
"We're supposed to get some better wind that will clear things out," said Air Quality Management District engineer Sarah Nave.
(You can reach Staff Writer Glenda Anderson at 462-6473 or firstname.lastname@example.org. The Associated Press also contributed to this report.)