ITD's recent avalanche season was one for the record books
Closed just 8.5 days from November through April - a record low
Some records are sacred – Joe DiMaggio’s 56-game hitting streak, Bill Russell’s 11 NBA titles in 13 years, "Gone With the Wind" ticket sales and revenue from 1939.
Some are just begging to be broken. ITD’s southwest Idaho Avalanche Forecast Unit is happy to comply.
Despite 230 inches of snow and 45 individual avalanche/debris slides, a 12-mile segment of Idaho 21 was closed a record-low of just 8.5 days during the 2012-13 avalanche season. Historically, “Avalanche Alley” is closed more often and for longer periods because of threats to the highway from steep slopes nearby.
It’s only the second time in history the road has been closed fewer than 10 days for an entire avalanche season. The 2009-10 season was the other exception, and forecasters were on duty then, too.
The notorious stretch of highway is home to approximately 60 known avalanche chutes and about 90 percent of all slides in the state that reach the highway. Only 26 of this year's 45 slides reached the road.
The district has used the services of a forecasting unit to monitor and prepare for avalanches with the goal of assuring the safety of travelers and reducing the number and duration of closures.
When the highway closes, there is a significant impact on mobility and commerce. The cost to the public for each closure on Idaho 21 is approximately $4,000 per day – excluding the effects of interrupting commercial traffic.
Another key factor considered in closures is time savings. The closest detour is 86 miles (approximately another 120 minutes) if the road is closed. It can be almost three times that distance if motorists drive all the way to the closure gates before being forced to turn around.
The numbers speak for themselves – closures were reduced by two-thirds last winter, despite about 65 more inches of snowfall.
Only 56 pounds of explosives were used this year to probe or bring down avalanches, which is considerably less than usual.
“We usually use around 250 pounds,” said Bill Nicholson, ITD’s southwest Idaho lead avalanche forecaster. “But the rain and warm temperatures made the explosives less effective.”
“The avalanche forecasting this season presented unique challenges as usual,” he added.
“Early snow followed by long dry and cold spells produced a weak snowpack. This was followed later in the winter by unusually warm storms, putting greater stress on the weak snowpack.”
"We are able to keep the closures to a minimum, thanks largely to a great staff of forecasters and a lot of assistance from the Boise National Weather Service office," Nicholson said.
Decades ago, the highway often was closed all winter. As recently as a few years ago, closures for 60 or more days each winter season were commonplace.
Future improvements
Nicholson said the forecasters plan to create an Idaho 21 web page this summer to assist travelers with their plans. It also will be on the ITD web page and be linked to the statewide 511 Traveler Services system.
The department’s research partnership with Boise State University also is progressing, as teams work on an infrasonic avalanche-detection system to assist with forecasting, explosive testing and a warning system if forecasters misjudge the extent of a hazard.
Nicholson said the system will provide “avalanche size and distance, as well as shot placement for explosives,” which will combine to “greatly improve safety and reduce closure times.”
Published 6-7-13