Two portions of Idaho 21 closed as avalanche risk poses ‘almost certain’ danger
Weather conditions have forced officials to close two sections of state highway north of Boise. They remained closed as of Tuesday.
The Idaho Transportation Department announced Friday that all lanes of Idaho 21 between Grandjean and Banner Summit were closed to traffic.
The 12-mile closure extends from milepost 93.7 to milepost 105.5.
The department then announced a second closure of 31 miles between milepost 41 at Granite Creek, two miles north of Idaho City, and milepost 72 in Lowman. The Idaho Transportation Department had previously reopened this area briefly over the weekend but closed it again Sunday.
The Grandjean section was closed because of avalanche concerns, according to the transportation department.
The Sawtooth Avalanche Center has issued an avalanche warning, listing the current danger as extreme in the mountains that Idaho 21 traverses near Grandjean and Stanley.
The center said its experts expected the danger to peak Tuesday night “with the final punch of a powerful multi-day storm overloading a very weak snowpack.”
It advised people to avoid all avalanche terrain, including flat ground below slopes steeper than 30 degrees.
“Natural and human-triggered avalanches large enough to bury people are almost certain,” the center said in a social media post Tuesday morning. “Some avalanches will be large enough to snap trees and damage structures.”
The section between Idaho City and Lowman was shut down after snow slides blocked the road Sunday, the Boise County Sheriff’s Office said. The sheriff’s office estimated it would take “several days” to clear.
That area received 24 inches of snow over the weekend, with another 18 inches predicted to fall this week, according to the transportation department.
