Avalanche-Prone Stretch Of Idaho 21 Closes This Morning


By Paul Johnson

Boise County, Idaho (KMVT-TV) - The 12-mile stretch of Idaho 21 between the Grandjean Junction and Banner Summit closed this morning at 7:30 a.m. as an avalanche safety precaution, the Idaho Transportation Department announced. The route will be evaluated for re-opening at noon today.
More than a foot of snow accumulated at Banner Summit over the weekend. No slides have occurred yet, but the avalanche risk is "considerable," according to ITD forecasts. The National Weather Service comments that "MAJOR WINTER STORM CONTINUES BRINGING STRONG WINDS AND HEAVY SNOWFALL TODAY. EXPECT A TOTAL OF OVER A FOOT BY THIS EVENING. THE HEAVIEST SNOW WILL FALL FROM NOW (4 AM MST) THROUGH NOON MST TODAY. WINDS WILL GUST OVER 50 MPH AT BANNER SUMMIT."
This will be the first closure of this section of road this winter.
During avalanche season last year, there were eight closures between Nov. 1 and March 31, totaling 21.5 days. A total of 50 slides tumbled down on the highway during that time.
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 avalanches in the state that affect highways.
For the latest highway and weather conditions, call Idaho Traveler Services at 5-1-1. For online updates, visit the website at 511.idaho.gov. Telephone and Web reports are available 24 hours a day and are updated as conditions change.
Despite more than 28 feet of snow and 50 avalanches, ITD snowfighting provides fewer closures
ITD's snowfighters devote much of their work week to thinking about highways and bridges, so that valley drivers don't need to. In fact, few efforts are as clearly linked to highway safety or are as beneficial to motorists as the snowfighting battles waged each winter in southwestern Idaho.
The sheer volume of traffic and travelers is a big factor: the region features the largest population base and geographical area in the state - lots of drivers and many miles of roads.
With more than 50 inches of snow accumulated in some mountain areas already this winter season, the annual battle is well under way. "When we have at least 20 inches at Banner Summit, there is potential for avalanches," said Idaho Transportation Department Avalanche Forecast Manager Bill Nicholson.
The Avalanche Forecast team, two full-time (Nicholson and Chantel Astorga) and two seasonal employees, began daily forecasting for slides in the notorious “Avalanche Alley” area between Grandjean Junction and Banner Summit Nov. 1. The 11-mile section is home to about 60 avalanche chutes and 90 percent of the avalanches in the state that affect highways.
“We evaluate the strength of the existing snowpack and the incoming stresses such as snow, water weight, wind and temperature to create an avalanche-hazard forecast," said Nicholson. "Our goal is close the highway before any avalanches release that could threaten motorists. Then we can clear the highway off safely and reopen it as soon as it is safe."
Click here for Nicholson's sound bite.
Following that plan, the unit has been able to reduce the average number of closure days on Idaho 21 significantly, despite routinely receiving more than 300 inches of snow in a winter season.
Last winter, for example, there were only 21.5 days of closure despite 338 inches of snow and 50 avalanches that tumbled down on the highway. The historic averages before and after the Avalanche Forecasting team are listed below:
With Avalanche Forecasting (last 3 years)
Avg. snowfall: 314 inches
Avg. closures: 16 days

Before Avalanche Forecasting (1999-2009)
Avg. snowfall: 227 inches
Avg. closures: 42 days
This is a tremendous service to drivers and businesses in the area. If the road is closed, the detour route adds 82 miles to the trip. The road used to be closed all winter long, every winter, as a precaution.
ITD is armed and ready to handle whatever the winter season brings. The region has switched to a winter schedule of two shifts of employees, changing between 2 and 4 a.m., that ensures 24-hour coverage on high-volume routes. ITD has 83 pieces of snowfighting equipment (de-icers, sanders, graders and plows) to clear more than 2,600 lane miles of roads in the region. This does not include another 37 loaders and backhoes that load sanders and clear turnouts.

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