Wind slabs load up tender snowpack, trigger natural avalanches near Steamboat Lake, Flat Tops
January 21, 2014
Steamboat Today reporter Ben Ingersoll audits the Colorado Mountain College course teaching snow safety in the backcountry. Find the story in Sunday’s Steamboat Pilot & Today.
Steamboat Springs — The recent cycle of frigid temperatures overnight and sunny, mild days has settled the upper levels of the snowpack in the mountains surrounding Steamboat Springs. But there recently have been strong signals in the form of natural avalanches, some of them very large, that the snowpack remains weak farther beneath the surface.
Retired avalanche forecaster Art Judson returned at midday Tuesday to Steamboat Springs from the Flat Tops Wilderness Area, where he reported spying the largest avalanche he has seen in that mountain range in more than 20 years, on 12,172-foot Dome Mountain. Looking through binoculars, he estimated it had a fracture line that was 12 to 15 feet deep across a half-mile distance.
Naturally triggered avalanches also were spotted northwest of Clark during the weekend.
Judson, a retired U.S. Forest Service avalanche forecaster with many years of field work, called the Flat Tops slide "absolutely massive." The big avalanche path was just one of 18 he saw on his automobile trip to South Routt.
"The Flat Tops avalanches were much larger than those north of Steamboat Lake," Judson said. "There was more snow, and the topography is conducive to blowing snow from long, upwind fetches above the avalanche starting zones. It's a very dangerous place when the snow is as unstable as it was leading up to this cycle."
North of Steamboat, another party saw more than one avalanche in the Willow Creek drainage between Steamboat Lake and Columbine during a ski tour Sunday.
Officially, the Colorado Avalanche Information Center is rating the danger in the Steamboat/Flat Tops zone as moderate at all elevations. However, avalanche forecaster Spencer Logan cautioned in his Tuesday morning report that the current weather pattern has done nothing to heal the problem with persistent slabs — buried layers of crust topped with hoar frost crystals — that can make the snowpack fragile in certain "weak spots."
Logan linked to a citizen report posted by touring skier Cody Perry, who was a member of the party that spotted avalanche paths and debris run-outs Saturday in the Willow Creek drainage.
In a phone interview Tuesday, Perry said it was plain to see that the gusty winds that blew through Routt County last week, creating wind slabs, played a role in the recent cycle.
"We saw up to five that failed on similar aspects, all ridge tops and with wind deposition," Perry said.
Logan said the current mixture of a relatively low probability of avalanches with the risk of significant consequences once a slide is triggered, poses tricky problems for backcountry travelers.
"Since we do not have magic weak-spot goggles, we have to think and evaluate the snowpack carefully," Logan wrote Tuesday. "Picking terrain with low consequences is the best strategy for handling the low-probability, but high-consequence nature of persistent slab avalanches."
Six days have passed since Steamboat received four-tenths of an inch of snow Jan. 15, ending a run that saw measurable snow fall on 13 of the first 15 days of the month.
Long-range snow forecasters said the next hope of freshening the ski slopes is a week away, when a mild storm front could bring light snow Jan. 29, but there also is a small chance of snow in the forecast for Wednesday night.
The National Weather Service was calling for increasing clouds Wednesday with a slight chance of snow between 1 and 4 a.m. Thursday.
Snow forecaster Joel Gratz, of Open Snow, wrote Tuesday that forecast models don't see the dominant high pressure system above the American West breaking down before the end of January.