Avalanche Warning Issued

U.S. Forest Service officials have issued an avalanche warning for central and southern Idaho mountains, singling out ranges in the Sun Valley area.

The increased threat comes from heavy snow on top of an unstable layer of old snow, said Matt Fugazzi, a National Weather Service meteorologist in Boise.

“It’s just waiting for a trigger,” he said.

Avalanches killed six people, most of them snowmobilers, during the weekend in Montana and Utah.

Bob Allen of Greylock Mountain Guides said avalanches typically strike on slopes of 30 degrees to 40 degrees. Steeper slopes tend to shed snow, while snow on flatter slopes is more stable.

“A lot of times, the trigger turns out to be a snowmobiler, skier or snowshoer,” he said.

Avalanche potential can increase when the weather warms and snow turns into rain, Allen said. Moisture seeps down and acts like a lubricant between layers of snow.