Wet weather and violent gusts strained an already unstable snowpack throughout the day and into the evening Tuesday, driving the Sawtooth Avalanche Center to issue an avalanche warning indicating very dangerous conditions across its entire coverage area.
Forecasters said avalanche danger was "high" throughout the Wood River and Sawtooth Valleys on Tuesday. They urged skiers, riders and snowmobilers to stay off of—and out from below—slopes steeper than 30 degrees, to avoid exposed terrain and to be careful of potential avalanche run-out paths.
"An intense storm bringing heavy snowfall, strong wind, and valley bottom rain is overloading a weak snowpack," the center stated. "Avalanches may impact roadways, trails and structures in the valley bottom. Avoid avalanche terrain and terrain exposed to avalanches from above."
The avalanche warning covers Galena Summit and the Eastern Mountains; the Soldier Mountains and those around the Wood River Valley; the Sawtooths and Western Smokies; and Banner Summit.
"Widespread avalanching is likely to occur," the Avalanche Center Forecaster Chris Lundy said Tuesday morning.
The National Weather Service issued a winter storm warning for the region on Tuesday, predicting gusts upwards of 55 miles per hour. Forecasts called for the storm to drop as as much as 20 inches of snow at upper elevations.
"If you must travel, keep an extra flashlight, food and water in your vehicle in case of an emergency," the Weather Service warned.
Even flatter ground near avalanche terrain carries risks. On Monday—before the storm amplified avalanche danger—snowmobilers remotely triggered a slide in the White Clouds from a mellower pitch a quarter-mile away, forecasters said.
Mounting avalanche risk prompted ITD to to close state Highway 21 northwest of Stanley ahead of Tuesday's storm. As of 5 p.m. on Dec. 27, that road remained closed. ITD stated it would reasses conditions Wednesday morning.
Said Lundy: "Any slide you trigger could be large enough to not only take you out, but also the vehicle you drove to the trailhead, the house you woke up in, and possibly the forest in your backyard."
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