The smoke obscuring the hills surrounding the Rogue Valley this week likely is caused by dozens of massive fires burning in Siberia, weather officials said.

"The winds are carrying the smoke all the way across the Pacific," said Marc Spilde, a meteorologist with the National Weather Service.

The Associated Press reported 67 fires were burning near Lake Baikal and on the Kamchatka Peninsula on Russia's eastern coast.

Spilde has monitored images from powerful satellites that show large patches of smoke across the Pacific Ocean.

Spilde said the fires have been burning for some time and the smoke has been hovering over the Pacific for several days. Heavy smoke has been reported from Medford all the way to Vancouver, B.C.

When the wind blows in from the west, this smoke seeps into the Rogue Valley.

"When it comes in, it doesn't stay around very long," Spilde said.

It's difficult to gauge when the smoke will enter the area because a think layer of clouds hangs above the ocean, making it hard to see the smoke, Spilde said.

There are no fires nearby in Western Oregon or Northern California, Spilde said.

"The closest fires are in the eastern side of the state," Spilde said.

The smoke from Eastern Oregon won't enter the valley because the wind is blowing from west to east, Spilde said.

Spilde added that the smoke should thin out in the coming days and that it doesn't pose a health threat.

"The air quality has not deteriorated since the smoke arrived," he said. "We have seen an increase in ozone, but that's about it."

Reach reporter Chris Conrad at 541-776-4471 or email cconrad@mailtribune.com.