The Idaho Transportation Department is closing State Highway 21 from Idaho City to Lowman on Thursday afternoon due to high avalanche risk.ITD says that the current weather pattern is likely to trigger avalanches in this section of the highway with anticipated closure beginning at 5 p.m. on Dec. 26. Motorists needing to use the roadway after Thursday afternoon will have to use an alternate route, such as State Highway 75.There are nearly 70 avalanche paths in this 11-mile stretch of SH-21, according to ITD, and avalanches are often triggered without warning, so there is no parking or stopping within this section of the road throughout the winter.