My ski partner and I stood on the broad, wind-worn cap of Scarp Ridge, a rim that balloons and narrows as it oscillates between Garfield Peak and Mount Emmons. The snowpack was fairly unremarkable for a sunny day in mid-December, and we were content with the coverage. “This escarpment is one of my favorite summer hikes — it’s incredible to see from this vantage point with snow,” I said to friend Billy Rankin, owner of Intuition Consulting and an Irwin Guides ski guide, as we snacked and looked southeast toward the vertical, north-facing precipice.
Our tour’s approach skirted two and a half miles above Lake Irwin to the summit of Mount Emmons — colloquially known as Red Lady — where, overlooking Crested Butte, we’d choose our descent. Aside from touring, our main aim was to field test a new digital tool in the GPS navigation app, onX Backcountry. Catalyzed by experts in Crested Butte, the app’s new layer, ATES (Avalanche Terrain Exposure Scale), is a system used by backcountry users to assess the risks of a given run by showing the level of avalanche exposure in the terrain, a key variable in addition to the snowpack. With the help of local avalanche experts, onX Backcountry became the first navigation app in the United States to integrate the ATES classification system. The mechanism had just launched 11 days earlier, and we were excited to test it out.
“This is one of my favorite ridges to ski!” Rankin exclaimed, which carried weight coming from a skier who’s worked in the Crested Butte backcountry for nearly three decades. Throughout that time, he’s seen the industry advance through knowledge and technology to help manage avalanche risk — including the ATES scale.
Rankin’s first ski guiding job in Crested Butte began in 1998 for the old Irwin Lodge, a 20,000-square-foot structure we’d passed on our snowmobile ride up to Scarp Ridge. Inventor Dan Thurman had purchased 100 acres of mining claims in 1977, built the snowbound lodge and leased surrounding Forest Service land to offer snowcat skiing to lodge guests. A larger, commercial cat-skiing operation opened in 1997. After it shut down in 2002, Rankin joined the Crested Butte Ski Patrol and forecasted for the newly founded Crested Butte Avalanche Center. When Irwin Guides and Eleven Experience resurrected the snowcat operation in 2009, Rankin jumped on board, and he’s worked there ever since.
“For years, we’ve heard wise avalanche gurus say, ‘There’s always terrain to ski every day.’ ‘If the snowpack is the problem, the terrain is the answer.’ ‘The more uncertainty there is, pick more conservative terrain.’ We put so much emphasis on terrain, but I feel most recreation users don’t have the tools to adequately categorize terrain in go or no-go decisions — a task professionals are challenged by daily,” said Rankin as we crested a high point near Scarp’s rim and pulled out our phones to open onX Backcountry.
“This is where ATES comes in. When a group goes through their planning process, they open their app with the ATES layer and see all the terrain categorized by simple, challenging, complex, and extreme,” explained Rankin, who became familiar with the app after Irwin Guides recently partnered with the Natural Selection Tour to host a snowboard competition at their backcountry operations, where Rankin guides.
“Well, that checks out,” I said, zooming into the ATES terrain shading, which classified our traverse along the southerly portion of the ridge as “low-risk terrain.” The north side of Scarp — which is flanked by severe, non-skiable cliffs — was rated complex and extreme. The shading even showed where the cliff bands receded at the top of routes. “I could see this layer being useful if you were studying a new zone and weighing risk,” I speculated.
Danger ratings for terrain aren’t new. Whitewater kayakers and rafters utilize rapid classification from I to VI. For North American rock climbs, you’ve probably seen labels like “class 1” or “5.13” from the Yosemite Decimal System. But a rating system isn’t common for backcountry skiing. According to Rankin’s mentor, avalanche expert Grant Statham, the first-ever terrain rating sequence for the sport was innovated by heli-ski operator Canadian Mountain Holidays (CMH) in 1993. Back then, CMH established three categories — A, B, C — for the zones where they dropped clients by chopper. Several years later, snow safety researchers Dick Penniman and Rene Boisselle proposed the Avalanche Terrain Risk scale with five tiers inspired by river ratings. Ultimately, Parks Canada pioneered the ATES system, Rankin explained. Statham was hired to lead the project in the wake of a significant avalanche in Glacier National Park in 2003, which buried 17 high school students, resulting in seven fatalities. Today, most trailhead maps in Canada display the area’s ATES ratings, helping to avoid similar tragedies.
The classification system goes from 0 — non-avalanche terrain like low-angle and densely forested slopes away from avalanche paths — to 5, which is extreme terrain with very steep faces, cliffs, spines, couloirs, crevasses, or sustained overhead hazard.
On the back end, ATES determines avalanche terrain exposure using 11 variables: slope angle and shape, forest density, terrain traps, avalanche frequency, runout zone characteristics, start zone density, exposure time, glaciation, route options, and interaction with avalanche paths. Now, backed by 20 years of scientific data, ATES iterations have since launched in Norway (where it’s called KAST), as well as New Zealand, Switzerland, France, and Austria. While Rankin and I are backcountry skiers, the ATES rating can be used for other snow travelers like Nordic skiers, snowshoers, snowmobilers, and snow bikers.
After visiting the prayer flags on Red Lady, Rankin and I skated to the top of our selected ski line, and I opened onX Backcountry to double-check the shading. “Our route is nearly entirely green,” I said as we prepared for the descent. After clicking on our radios, Rankin dropped first, yelling, “Have fun and find the goods!”
A few months later, I pulled on my pack at the base of Ruby Peak alongside ski partners Eric Phillips and Andy Sovick, the founder of Beacon Guidebooks. When onX Backcountry first approached Sovick in 2020 about digitizing the ski routes across the company’s 16 published ski atlases, Sovick celebrated. Uploading the routes into a user-friendly app would help skiers access information in the field, Sovick explained as our trio skinned across the wide-open approach. And computerizing ATES with an algorithm would help the rating system become more widely available to a burgeoning population of backcountry enthusiasts. Today, more than five million backcountry skiers and splitboarders venture out nationwide, a population that nearly doubled during the pandemic, according to the Snowsports Industries America 2022-23 Participation Report. To actualize his vision, Sovick joined onX Backcountry as senior content manager in 2023.
Sovick’s passion for guidebook creation started decades ago. While attending Fort Lewis College in 2000, he and his tour partners carried disposable cameras and compiled photos into binders, highlighting routes in the San Juan Mountains. Sovick started exploring the Crested Butte backcountry on skis in 2005. By 2013, he settled in the Gunnison Valley and published Backcountry Skiing Crested Butte, Colorado, a 36-page backcountry ski guidebook with 11 zones and 50 descents. Met with popularity, there was a demand for more guidebooks, and Sovick launched the publishing company Off Piste Ski Atlas (now Beacon Guidebooks) that same year. Since then, the company has produced guides in five states, 13 maps, an avalanche rescue field guide, and a children’s book, Squeak Goes Backcountry Skiing.
As soon as I reviewed the research and applied the scale to terrain, I got excited — ATES really clicked for me
All the while, Sovick was trying to solve a problem. “We were describing the terrain that people often skied using objective, ambiguous words like ‘frequent slider’ and ‘sketchy’ — terms that weren’t backed by science and standardized. I wanted to discuss terrain in a more objective, understandable way,” he explained as we reached the southeast ridge and kicked into the slope where we’d transition to bootpack.
As I’d learned in my own education, Level 1 and 2 Avalanche Training courses teach students that terrain is a critical variable to consider alongside weather and snowpack, which are dynamic. Terrain is static, which is why ATES ratings are fixed and based on constant parameters. “A lot of people leave that early education of avalanche safety feeling confused and uncertain about how to know their terrain and explore without getting in over their heads,” said Sovick as we turned and started booting up the steep face.
In 2014, Beacon Guidebooks author Matt Schonwald, who penned the atlases for Mount Baker and Snoqualmie Pass, brought the concept of ATES to the table, which he’d seen in a Parks Canada article. “As soon as I reviewed the research and applied the scale to terrain, I got excited — ATES really clicked for me,” said Sovick, who integrated the system into Beacon Guidebooks in 2016. Each table of contents outlines the five levels of terrain complexity, and every route is labeled with a corresponding number from that spectrum. The gradation helps users select less complex terrain, notice hazards, and filter out subjectivity when route planning with ski partners.
A virtual version was the next step. Employing an algorithm called autoATES, developed by Alaska-based researcher John Sykes, the onX Backcountry program processes terrain characteristics using satellite imagery like slope angle, forest density, start zone density, and runout zone characteristics. To dial in the rating, local avalanche professionals validate the results and check the remaining six variables such as avalanche frequency and magnitude. “We need help from forecasters who’ve watched avalanches over a long time — satellites and algorithms can’t do that for us. We have to use the human brain,” said Sovick as we looked over at Mount Owen and took our closing steps onto Ruby Peak’s summit.
Crested Butte Avalanche Center’s (CBAC) Lead Forecaster, Zach Guy, was “heavily involved in the ground-truthing of the layer,” he shared in an interview. It was a CBAC goal to create an ATES map for backcountry travelers “to visually show the severity of avalanche terrain,” explained Guy. Partnering with Sovick and onX Backcountry was a natural fit.
During the fact check process, they identified discrepancies. For instance, if “the ATES layer was missing a runout zone based on historical avalanche data, and I knew based on my 10 years of field experience that one existed, we’d figure out why and tweak the parameters,” explained Guy, who spent a year reviewing the layer alongside Sovick, before wrapping up the project in November 2023. Ultimately, Guy and Sovick designed a four-tier scale for the app. It was too difficult to confidently determine boundaries for level 0 — as in, no avalanche terrain — like in Gothic, for instance, where runout zones can be historic. So far, the app’s ATES layer is live in 16 backcountry ski zones across Colorado, Utah, and Montana.
As with any tool used for travel in avalanche country, there’s no silver bullet. The autoATES algorithm creates a model and, like weather forecasts, is imperfect.
“There are limitations with input like the tree cover and slope angle. The data derived from satellite imagery is not a perfect representation — trees are missing or rollovers in a slope aren’t captured at scale,” said Guy, adding, “We’re drawing boundaries and in reality, nature is fuzzier.”
While Sovick, Phillips, and I waited for the snow to warm up on the 12,641-foot summit, I checked the onX Backcountry app to see how ATES graded our route. After our “challenging” Level 2 approach, the landscape had transitioned into a “complex” Level 3 zone with a “large expanse of steep, open terrain.” Thinking back to our climb, that transition was exactly where I had paused and slid on a binding crampon for the steep traverse across the solid face. While the app’s definitions are vague, as Guy had pointed out, I could see how this tool could support group communication and planning — as long as it’s not replacing other foundational safety steps.
“We should be open to any little tool that helps us stay safer and make better decisions — especially if it helps save our lives — but only if we apply our own experience. Regardless of the technology, we have to pick our heads up, look around, and use our own brains,” said Sovick, before dropping into Ruby Peak’s southeast bowl, leaving behind a sweeping carve in the corn.