BOISE COUNTY, Idaho — Update: Highway 21 was open again Monday morning. Previous story continues below.
State Highway 21 is closed in both directions between the Grandjean junction and Banner Summit due to avalanche danger, the Idaho Transportation Department (ITD) reported.
This stretch of highway, nicknamed "Avalanche Alley," closes several times each winter because of avalanche risk or avalanches blocking the roadway. State Highway 21 is closed from milepost 93.7 to milepost 105.5.
Highway 21 is also closed northeast of Idaho City to Lowman, from milepost 48 to milepost 72, ITD reported Saturday afternoon.
The Sawtooth Avalanche Center lists avalanche danger as High for all four zones in its region Saturday, including Banner Summit, Galena Summit and Eastern Mountains, Sawtooth and Western Smoky mountains, and the Soldier and Wood River Valley mountains. Travel in those areas is not recommended.
The avalanche danger scale consists of five levels, from least to highest amount of danger: 1 – Low, 2 – Moderate, 3 – Considerable, 4 – High, 5 – Extreme.
ITD said State Highway 21 is closed in both directions until further notice at "Avalanche Alley." Crews plans to reassess conditions between Grandjean and Banner Summit at 7 a.m. MT Sunday.
In a Facebook post Saturday morning, the Sawtooth Avalanche Center said "very large natural avalanches are almost certain" in its forecast area.
For updates on road closures across Idaho, drivers should check Idaho 511 and ITD's Twitter account.
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