Idaho’s ‘Avalanche Alley’ along Highway 21 closes Wednesday afternoon. Here’s when and why

Shaun Goodwin
·1 min read
Closure signs put up by the Idaho Transportation Department on State Highway 21 for the potential of avalanches.

Idaho’s notorious “Avalanche Alley” along Idaho 21 will be closed on Wednesday afternoon as another round of snowstorms and rain sweep through Idaho.

Due to a high avalanche risk, the Idaho Transportation Department plans to close Idaho 21 between Grandjean and Banner Summit. Heavy snow and rain, which passed through Boise Wednesday morning, will likely cause avalanches along the 11-mile highway stretch between Lowman and Stanley.

ITD anticipates closing Idaho 21 between the locations mentioned above at 4 p.m. but may close it earlier if weather conditions worsen.

Motorists traveling from the Treasure Valley to Stanley — or vice versa — are encouraged to make the trip immediately or plan an alternate route. If travel past the closure time is still necessary, ITD recommends using Interstate 84 until Exit 95 to U.S. Highway 20 at Mountain Home before heading north on U.S. Highway 75 to Stanley.

Heavy snow in Idaho last week resulted in two vehicles trapped by an avalanche along Idaho 21. All occupants were saved unharmed and escorted from the canyon.

According to ITD, there are approximately 70 paths where an avalanche can occur, all of which can be triggered without warning.

Idaho 21 is just one of three highways in the United States that fall under the “High” category on the Avalanche Hazard Index, along with State Highway 210 in Utah and U.S. Highway 550 in Colorado.