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First Idaho 21 avalanche closure of season last weekend

The 12-mile stretch of Idaho 21 between the Grandjean Junction and Banner Summit closed Friday afternoon (Jan. 10) at 4 p.m. as an avalanche safety precaution, re-opening Sunday evening at 4 p.m. when the threat subsided.

The decision to close the route proved to be wise.

During the closure, nine slides affected the highway; four were man-made, triggered by explosives launched purposefully to bring down caches of snow likely to release anyway, and the remainder occurred naturally.

The notorious "Avalanche Alley" section between the Grandjean Junction turnoff and Banner Summit is home to about 60 avalanche chutes and 90 percent of the Idaho avalanches that affect state highways.

The first avalanche closure during last avalanche season occurred a few weeks earlier, on Dec. 16.

Despite 45-50 slides each year and more than 250 inches of snow on average, the forecast team has reduced closures by more than 60 percent since they began forecasting slides and slide threats five years ago.