The Idaho Transportation Department will close State Highway 21 from Grandjean to Banner Summit this afternoon due to high avalanche risk.
A weather system bringing rain and snow is likely to trigger avalanches in this section of highway. The anticipated closure will begin at 4 p.m. today. However, actual weather impacts may require an earlier closure.
Motorists needing to use the roadway are advised to make the trip immediately or plan to use alternate routes. The alternate route between the Treasure Valley and Stanley area is to travel east on Interstate 84, exit in Mountain Home at Exit 95 to U.S. Highway 20 and then head north on State Highway 75.
The ITD avalanche crew monitors the snowpack along this section of highway in order to forecast the risk of avalanches large enough to reach the roadway. This practice allows the department to keep the highway open during the winter months with a reasonable confidence of safety for the traveling public.
There are around 70 avalanche paths in this 11-mile stretch of SH-21. Avalanches can be triggered without warning. For this reason, there is no parking or stopping within this section of road during the winter.
The highway will reopen when the snowpack has stabilized and the risk of active avalanches is reduced. Updates on closures and openings will be posted on 511.idaho.gov.