Density a factor; more to come, verging on a record
By Katherine Nettles
With more than six feet of snow—and counting—during the first two weeks of March in some areas across the state, Colorado has seen multiple fatalities, evacuations, road and ski area closures, damage to infrastructures, and even a town cut off from its southern access point.
The state’s significant snowfall and snow density have caused historic avalanche activity, with more than 550 avalanches across the Western Slope, and experts say there is more to come.
As Crested Butte Avalanche Center lead forecaster Steve Banks describes it, “We have seen other events that have been similar to this.” But not very often.
For example, Banks points out that the storm clusters in March’s first 11 days produced almost as much snowfall as the entire month of January 2017. “And January 2017 was when we coined the term ‘snowpocalypse,’” he adds.
Of at least equal importance to snowfall is the snow’s density, or water content—also referred to as Snow Water Equivalent, or SWE. As anyone who has shoveled their driveway or even their car in the past couple of weeks will know, the recent snowfall has been heavy. “We are looking at about [a total] of 310 mm of water, whereas we had 375 mm [total] in January 2017,” reports Banks.
The classic quote Banks recites is that abnormal or extreme weather events create abnormal or extreme avalanche events—both of which Colorado has seen as of late.
In Summit County, the heavy snow created five new avalanche paths.
Ski area Arapahoe Basin had to shut down for two days, while others had limited openings and myriad lift complications. Front range weather issues resulted in some flights into Gunnison being cancelled this week.
Interstate 70 west of Frisco remained closed for the day on March 7 due to avalanche activity taking out a gas line, and threatening the interstate and drivers.
Red Mountain Pass (Highway 550) near Ouray has been closed indefinitely since more than 20 avalanche paths left massive amounts of snow and debris in their wakes and closed off access to Ouray from everything to the south.
Breckenridge reported an in-bounds avalanche after opening an area to the public on March 9. In Aspen, a mile-wide avalanche, “probably the largest ever,” in Colorado according to Banks, occurred on that same day.
The backcountry and the urban interface have also proved dangerous in Crested Butte. Locally, a young man was killed in a roof slide in Crested Butte South over the weekend, while several other people were trapped or buried in similar roof slide situations. Crested Butte officials closed down Red Lady Avenue at Fourth Street and closed the area at First and Elk near the old Kebler Pass road last week to prevent accidental avalanches, even small ones, from surprising pedestrians or travelers. “There are common places where people might walk their dogs or go sledding, and not pay very much attention to it,” says Banks. The areas have since re-opened.
A natural avalanche coming off the eastern face of Gothic Mountain hit a cabin last week, reportedly knocking down some very large timber. Banks estimates that the slide took out approximately 100 aspen trees, “as if they were matchsticks.”
The northeast bowl of Gothic, which Banks says does slide fairly often, ran much larger than usual, spreading across the East River Valley and hitting the outhouses at the Judd Falls trailhead. “That’s a good indicator that we are going to see large avalanches,” he says.
billy barr, a long-time caretaker of the Rocky Mountain Biological Laboratory (RMBL) cabins and research facilities, wrote on Facebook that the “Bench” slide on Gothic was “the largest this has run in my 47 winters.”
A cabin in Taylor Canyon that sits in a fairly dense forest, next to a steep hillside and close to the road, was struck by an avalanche on March 8 as well. Nobody was there at the time.
In Lake City, the home of Hinsdale County sheriff Justin Casey and his two daughters was hit by an avalanche that destroyed the home and injured all three of them on Tuesday morning.
“We have seen large avalanches, bordering on historic size… but not as big as other areas,” says Banks. He credits this to the area around Gunnison County having had more consistent snowfall throughout the year, and in general a deeper snowpack is a more stable snowpack, he says. The Ruby Range and Paradise Divide are reportedly trending toward more stable.
“That said, we do have several persistent weak layers buried deep in the snowpack, near the ground. And we saw weak layers created with dry spells in January and February. It’s interesting to see which layers they fail on. The February 28 weak layer has failed, the January layers have failed, and others as far back as the October snowfall. There hasn’t been one weak layer that has been the culprit; there have been a variety.”
Banks repeats that a lot of the problems are due to the amount of snow and its density, which typically is 7 percent to 10 percent. “In these storms, we have seen 10 percent to 12 percent and even as high as 16 percent. So that means we have a lot of volume in the snowpack. That increases the potential for avalanches to be bigger and run farther down.
“That is why we are also seeing roof-alanches. That water leaches out and hits either the metal roof or a weak layer,” Banks explains.
As another storm comes through and a high pressure system awaits in the forecast, the Colorado Avalanche Information Center and the CBAC warn against anyone growing too comfortable.
“We’re pretty lucky here because we don’t have a lot of large vertical relief that threatens areas, homes, roads… but it’s not out of the question to have those problems. We have a lot of small but steep hillsides,” says Banks.
On that note, the CBAC warns residents and visitors alike to be careful and mindful at all times of their surroundings. Many condos are built on steep banks, which can avalanche. “It might seem like fun to play in a snow banks, but people need to be aware of what is above them and around them—even in the town limits,” Banks says.
Last, most backcountry travelers are more aware of the dangers and where they go. Yet, Banks warns that a period is likely to come with a combination of low avalanche likelihood and high consequence. “A threat is mostly on the eastern portion of our mountains, where we have had a shallower snowpack near Brush Creek and Cement Creek,” he summarizes, in addition to places that have avalanched already.
The forecasters, ski patrol and others involved in keeping up with these storm cycles are not ready to stand down. Banks says that while these prolonged cycles can get tiresome, with “a lot of early mornings, a lot of data to share with each other, other areas, and getting out to the public,” it’s also an amazing phenomenon to witness. “This is more interesting for us, and its more interesting than a two-week dry spell,” he says.
While he is still out in the field daily, Banks says he is “staying away from avalanche terrain, very cognizant of any paths near or above me. A good example of that is that Irwin ceased operations for two days, due to avalanche paths that threatened the roadway and the commute up to Irwin. That has only happened once in the past eight years” he says.