A special backcountry avalanche warning was issued Sunday for the mountains of Northwest Montana.

Avalanche danger is "high" for areas between 4,500 feet and 7,500 feet, according to Flathead National Forest avalanche expert Stan Bones.

Travel in avalanche terrain is not recommended, according to the advisory. The warning applies to the Mission, Swan, Flathead, Lewis and Continental Divide mountain ranges.

Heavy snowfall plus strong winds have increased the avalanche danger. The Whitefish and Swan ranges received 15 to 20 inches of snow, with more than 2.5 inches of water content, on Saturday.

"The combination of deep new snowfall, wind and rapidly cooling temperatures is creating very unstable snow conditions," Bones said in his advisory. "Backcountry recreationists and travelers should avoid all travel in avalanche terrain until snow conditions have the opportunity to settle."

The warning comes a day after the third fatal avalanche incident this month in Northwest Montana.

Two snow bike riders were caught in an avalanche in the Skyland Creek area near Marias Pass, killing one man from Cut Bank.

According to a report from Bones: "Both riders were partially buried, one more deeply than the other. The least buried was able to dig himself free. A search located his companion with at least one foot protruding from the snow. Unfortunately when uncovered, the companion could not be revived."