Smoke from large forest fires in Northern California has been dimming the sky over Lane County, but the pollution is so high in the atmosphere that it hasn't hurt ground-level air quality in the Willamette Valley, authorities said Monday.

The smoke is about 6,000 to 9,000 feet up, creating a high-elevation haze, said Laurel McCoy at the Portland office of the National Weather Service.

Whether the smoke will get drawn down closer to ground level in the next few days remains uncertain, officials said.

The air quality in the Eugene-Springfield area and Cottage Grove was rated "good" on Monday, and the air quality in Oakridge was rated "moderate," according to data from the Lane Regional Air Protection Agency's monitoring stations.

"But air quality can change quickly. It wouldn't be surprising to see moderate-level air quality in the next few days" in the valley, said Jo Niehaus, spokeswoman at the air agency. "Moderate" is one step worse than "good."

McCoy said the high-elevation smoke has prevented ground-level air from cooling off as much as it normally might at night.

"The hazy skies are trapping the heat a little bit at night," she said.

In some eastern parts of the state, the high-elevation smoke is also capping lower-elevation smoke from Oregon forest fires, preventing the lower-level smoke from "mixing and getting dispersed," she said.

Much of the eastern two-thirds of the state has "moderate" air quality, due to in-state and California forest fire smoke, noted Greg Svedlund, a spokesman for the Oregon Department of Environmental Quality.

The high-altitude plumes of smoke from California intensified over the weekend as the California fires grew rapidly and winds shifted, pushing the smoke northward.

Svedlund said he expects air quality over much of Oregon -- especially Southern and Eastern Oregon -- to worsen over the next couple of days.

McCoy said cooler weather may move into Western Oregon from the Pacific Ocean as the week progresses, possibly keeping Willamette Valley air relatively clean.

But Svedlund said the overall outlook for the state's air quality for the next several weeks is grim, given the large California fires, winds blowing from the south, the large number of forest fires in the state, and the continued possibility of thunderstorms sparking new fires over the next number of days.

"Over the next six weeks, we're going to be in a tough situation," he predicted.

On the Oregon-California border about 15 miles southeast of Ashland, the Beaver Creek Complex has burned 36,000-plus acres. The blaze was started by lighting on July 30.

Other lightning strikes in late July caused a string of forest fires in Northern California that have also grown into substantial blazes.

The July, Coffee, Little Deer and Beaver fires are burning in roughly 25,000 acres near the Oregon border.

To the south of them, in Lassen National Forest, new fires are burning on roughly 66,000 acres of forestland.

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