Colorado in uncharted avalanche territory as the climate changes

March 16, 2019

David O. Williams, The Gazette

VAIL • As snow scientists and highway officials literally and figuratively dig out from under a mountain of snow left by Wednesday’s bomb cyclone and a recent 5-foot-plus heavy, wet, avalanche-triggering snow cycle in the mountains, they’re collectively trying to grapple with what comes next and how it all connects to climate change in Colorado.

For the Colorado Department of Transportation, which has been dealing with historic avalanches along the Interstate 70 corridor into the mountains — along with stranded motorists scattered across the eastern plains by the bomb cyclone — that means coming up for air over the next week when milder weather is forecast and getting a handle on road repairs, melting and rock slides.

“It’s also really just about trying to get our folks rested,” said CDOT’s Tracy Trulove, who’s based in Glenwood Springs.

“We’re taking this break in the weather to try to repair some of the road damage. This kind of winter is really tough on us for potholes and sections of the roadway that get damaged. And our team will be taking advantage of this drier week to be sure we are well-stocked with what we need if we’re going into another cycle like this.”

Longer-term forecasts are calling for the return of this season’s consistent snowstorms this month, and avalanche experts and road crews are bracing for the worst. Part of the problem this season was above-average snowfall building up on steep mountain slopes without sliding. Then a very moist, Pacific storm cycle fell on top of it, triggering huge avalanches down to I-70.

It’s tough to connect one heavy, wet, Pacific storm cycle to climate change, said Brian Lazar, deputy director of the Colorado Avalanche Information Center, and he added such storms are not all that unusual in Colorado and climate change is playing a role.

“We often talk about things in terms of snow-water equivalent, and so we’re seeing these storms that are dropping 3 to 5 inches of water in a 24-hour period and that’s a significant and rapid load to the snowpack,” Lazar said, referring to the mountain storms this month that triggered huge avalanches along I-70 in Summit and Eagle counties.

“Maybe the number of them this year and just how wet and kind of juicy they’ve been is a little bit out of the normal,” Lazar added. “That’s not inconsistent with predictions of a warmer climate. That warm air can kind of just hold more moisture. Colorado is typically colder and drier, but if the air over Colorado were to get warmer, it can produce wetter storms.”

The Colorado Avalanche Information Center works with CDOT to predict avalanche paths along the state’s network of roads, with eight forecasters trying to figure out when and where avalanches will occur along the roads CDOT maintains. The avalanche center also has a team of backcountry forecasters.

“Avalanches were hitting along I-70 but look at other places that were also experiencing backcountry things — the (slide) in Hinsdale County that took out the sheriff’s house,” Trulove said, referring to a March 12 avalanche near Lake City. “Think about CAIC and how busy they stay with us, but they have that (backcountry) piece of what they do, too.”

During the March 13 bomb cyclone, while things were relatively quiet in the high country — just the usual spun-out semis and passenger vehicles shutting down mountain passes — Trulove said she was getting calls from Grand Junction media about rock slides. This was all just a few days after I-70 was shut down so crews could go up in helicopters and drop charges on slide paths.

CDOT has a specialty unit in its maintenance department of about 70 workers statewide who are trained in avalanche mitigation, including using explosives to set off controlled avalanches that can be cleared while the road is closed to vehicle traffic, which is what happened on March 10. Seven of those workers concentrate on Vail Pass and the west side of the Eisenhower Tunnel.

A week before that in an unplanned event on March 3, an avalanche in Summit County’s Ten Mile Canyon came all the way down to I-70, impacting vehicles but miraculously not causing injuries. That prompted CDOT mitigation in the area that hadn’t been necessary since the 1980s.

CDOT contracts helicopters, removes their doors and sends its avalanche experts up along with Colorado Avalanche Information Center forecasters to drop explosives on key “start zones” where a slide historically is most likely to trigger. Such flights are more common in the steeper, more remote reaches of the San Juan Mountains and much more rare along I-70, Trulove said.

Trulove said CDOT also has a relatively new administrative group focused on risk and resiliency along the I-70 corridor, factoring in climate issues. But trying to better predict avalanches by building climate change and warmer, wetter snowstorms into forecasting models will be difficult, experts say.

“This is what we would expect, that a warmer ocean and a warmer atmosphere mean that the atmosphere can hold more water and potentially rain or snow at greater intensity than in the past,” said Jeffrey Deems, a research scientist at the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder.

“One of the challenges is that the typical sort of climate standard and projection scale is a much longer timeframe than that over which avalanches operate,” Deems added. “What avalanches care about is this storm or this storm sequence and potentially this season as far as how weak layers develop and whatnot.”

Which means a much bigger sample size is needed to be able to say that climate change is making avalanches in Colorado’s high country more or less likely. The variability of snowstorms and water content will always make it tough to accurately forecast when and where slides occur.

What isn’t debatable is that Colorado is getting warmer and that previously unheard of midwinter rain events are becoming more common in the Colorado high country, said Lazar, who has a master’s degree in engineering focused on snow and ice mechanics.

“As avalanche professionals, the challenge for us is that we often draw on careers of observations and how we’ve seen storms play out in terms of avalanche cycles,” Lazar said.

“But we’re starting to see storm events that we haven’t quite seen before, and so our challenge is going to be going back to first principles and thinking about how avalanche cycles and avalanche conditions may change in a changing climate.”

Deems, who works for the National Snow and Ice Data Center and also does water assessment for the National Oceanic and Atmospheric Administration, concurs that Colorado is warming and that rain and wetter snow are therefore becoming more common. Known for its famed “cold smoke” powder storms, Colorado residents need to get used to more coastal conditions.

“The instrument record does bear that out, that we are seeing increased rain fraction and we are seeing higher snow lines in particular storms,” Deems said. “We’re seeing a shorter snow season, et cetera. Now making the leap from that to avalanche activity is where it gets a little more dodgy.”

Big and unexpected avalanches can occur in low snow years, he points out.

“You don’t need a big year to get a big avalanche cycle,” Deems said. “We can have a really crappy year with a ton of depth hoar and then get one of these atmospheric rivers on top of it.”

That’s what happened early in 2012, when there was very little snow deep into January and then a couple of big storms. Extremely rare inbounds avalanches at two Colorado ski areas — Vail and Winter Park’s Mary Jane — claimed the lives of two skiers on Jan. 22 that year.

Seven years before that, on May 20, 2005, water loading on the steep Pallavicini run at Arapahoe Basin caused a wet slab avalanche that killed a Boulder man in an inbounds slide. Wet slab avalanches move in one big concrete-like mass that can be slower but more destructive.

“That’s one of the other things that we should be looking towards with a warming climate is an increased frequency of wet-snow events and or wet-snow events earlier in the season than we typically see them,” Deems said.

And the idea of trying to base predictions on averages is becoming much more difficult, Lazar said, pointing to last season’s historically low snow totals followed by this season’s above-average snowfall.

At this point in the ski season last year, Vail and Beaver Creek needed a mid-April storm cycle just to get over the 200-inch seasonal total, which is well below the 330-inch seasonal average for the two resorts. This season, Vail has topped 300 inches, with more than a month to go in ski season, and Beaver Creek is just under 300.

“Talking about average is becoming more and more meaningless because we just have a lot more variability going on,” Lazar said.

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