How Avalanche Terrain Is Being Re-Rated in the Canadian Rockies

For decades, avalanche safety advice has often boiled down to a single number. Thirty degrees. Thirty-five. Stay below it and you are safe. Cross it and you are not.

The reality, avalanche experts say, has always been more complicated.

A new update to the Avalanche Terrain Exposure Scale, known as ATES 2.0, aims to reflect that complexity while making terrain risk easier to understand for everyday users. The system, used across Canada to classify avalanche terrain, now expands from three categories to five and introduces new ways to communicate risk for activities like waterfall ice climbing.

For mountain guide and avalanche forecaster Grant Statham, the update reflects two decades of change in how people use the mountains and what they need to know to stay safe.

“With respect to avalanche risk, ATES ratings help people understand the difference between a high-risk trip and a low-risk trip,” Statham said. “And now, with the updated system, a no-risk trip.”

Why the old system was no longer enough

ATES was first introduced in Canada in 2004 as a way to rate terrain based on exposure to avalanches, not on daily snow conditions. It classified trips as Simple, Challenging, or Complex. Almost immediately, Statham said, something was missing.

“It became clear right away that we needed a classification for no avalanche risk,” he said. “The majority of park visitors want to avoid avalanche risk altogether.”

At the same time, the upper end of the scale was also changing. Advances in equipment, mapping, and backcountry access have pushed more skiers and climbers into terrain that earlier generations rarely touched.

“High-level skiing has changed a lot,” Statham said. “Many people are venturing into more serious terrain than they used to. We needed a way to show another level at the top end.”

ATES 2.0 adds two new categories to address both gaps.

Class 0 describes terrain with no exposure to avalanches at all. Class 4, at the opposite end, captures what Statham calls “tiger country.”

“Big, steep, risky, high-frequency avalanche terrain,” he said.

Why slope angle alone can be misleading

Slope angle remains one of the most common decision tools used by recreational backcountry users. It is simple, measurable, and useful. But Statham says it tells only part of the story.

“Slope angle is a good basic choice for measuring the slope you are about to ride,” he said. “But it fails to capture adjacent slopes, slopes overhead, terrain traps, and other important subtleties.”

In practice, that means focusing only on the ground directly under your skis or boots can be misleading. A slope that feels safe because it is low-angled can still sit beneath much steeper terrain above it. If an avalanche releases higher up, it does not matter how gentle the slope below is.

That steeper terrain above is known as a starting zone, the place where avalanches typically begin. Once released, snow can travel far downslope into flatter areas known as runout zones, where people may feel falsely protected because the terrain no longer looks steep.

Other features can magnify the danger. Terrain traps, such as gullies, narrow creek beds, cliffs, or dense trees, can concentrate moving snow or increase the consequences of even a small slide. What might be survivable on an open slope can become deadly in confined terrain.

“Avalanches don’t care where a GPS line is drawn,” Statham said.

This is why ATES focuses on exposure, not just steepness. The updated system considers how all these elements interact: where avalanches are likely to start, where they might travel, how often they occur, and what happens if someone is caught in them.

Behind the scenes, ATES 2.0 evaluates factors such as starting zones, runout paths, terrain traps, slope shape, forest cover, and avalanche frequency. Those technical details are then translated into simple terrain classes designed to be understood at a glance, even by people without formal avalanche training.

What this means for the Bow Valley

While ATES is used across Canada, its relevance is particularly acute in places like Canmore and Banff, where communities sit directly beside large, steep mountain terrain and where recreational use continues to grow.

For local users, Statham says one of the biggest benefits of ATES 2.0 is clarity.

“It helps people completely avoid avalanche terrain if that’s their goal,” he said.

The update also pairs with emerging automated mapping tools known as Auto-ATES, which break terrain into smaller zones rather than assigning a single rating to an entire route.

“Once Auto-ATES has been fully implemented, people will have much higher-resolution terrain ratings,” Statham said. “You can see how the trip you’re planning is threatened, rather than just seeing one overall rating.”

That finer scale is illustrated in mapping examples from the Icefields Parkway and Bow Summit area, where different parts of the same landscape carry very different levels of exposure.

How ATES fits with avalanche forecasts

One common misunderstanding is that ATES replaces avalanche bulletins. It does not.

“ATES is only about terrain, not snow,” Statham said. “It tells you the severity of the terrain you’re choosing. The avalanche forecast is where you learn about the current snow and avalanche conditions.”

In Canada, that daily forecast is issued by Avalanche Canada, which publishes regional avalanche bulletins throughout the winter. Those bulletins describe how unstable the snowpack is on a given day and where avalanches are most likely to occur.

In practice, the two tools answer different questions. ATES asks where you are going. The avalanche bulletin explains what conditions you are likely to encounter that day.

Used together, they allow people to reduce risk by matching terrain choices to current conditions, choosing lower-exposure terrain on higher-danger days and understanding when and where even experienced users should dial things back.

A note on automated maps

Auto-ATES mapping is expanding rapidly, but Statham cautions against treating digital boundaries as exact.

In Alberta, automated ATES maps are already being used in places like Alberta Parks’ Auto-ATES mapping for Kananaskis, and similar approaches are increasingly informing trip-planning tools, GIS layers, and park management decisions. As the technology develops, higher-resolution terrain ratings are expected to appear more widely in public-facing maps.

“These are computer models and they come with error,” Statham said. “Do not consider the lines on the map to be exact. Think of them as a general representation of the terrain.”

Most importantly, he said, users should avoid making single-slope decisions based solely on an automated map. Auto-ATES is best used as a planning tool that highlights areas of concern, not as a substitute for on-the-ground judgment or situational awareness.

Practical takeaways

For people who want to enjoy winter travel without becoming avalanche experts, Statham’s advice is straightforward.

“Learn to use the ATES system and stick to Class 0 or Class 1 terrain,” he said. “Or go with experienced friends you trust, or a professional guide, if you’re heading into Class 2 and above.”

“There are many beautiful places to go in winter that don’t have avalanche risk,” he added. “But you need to know where those are.”

In the end, ATES 2.0 is less about adding complexity and more about making an invisible risk visible. In a mountain landscape where terrain never changes but people do, that clarity may be its most important update.

Resources

Avalanche Canada, Daily Avalanche Bulletins:
https://avalanche.ca

Avalanche Canada, Trip Planner (ATES + Forecasts): 
https://avalanche.ca/trip-planner

Parks Canada – Winter Safety and Avalanche Information:
https://parks.canada.ca/pn-np/mtn/securiteenmontagne-mountainsafety/avalanche/echelle-ratings