When we think about avalanche conditions we often think about things like wind-loading, snow coverage, slope angle and temperature of snow as layers add up. One of the things we may not think about is the out-of-season factors that impact our slopes and the likelihood of an avalanche, one of which is the aftermath of forest fires that impact slopes and avalanche conditions once the snow begins to fall.
As we begin March with hopes of more snow to come, it’s important to think about out-of-season effects that may play a part in our backcountry adventures. The Exponent spoke with a retired Bridger Bowl Ski Patroller, Patrick Davidson, about current snow conditions and the impact of recent forest fires on pre-existing slope conditions.
Davidson was part of the ski patrol in the late 90s, and still regularly skis at Bridger Bowl and enjoys backcountry skiing at History Rock, among other local spots. Like many avid backcountry skiers, he takes pride in learning about avalanche conditions and safety when enjoying the surrounding mountains.
Davidson said the low levels of snowfall the region received this year may lower the probability of a slide. However, with unseasonably warm and frigid temperatures, we’ve seen inconsistent layering which could lead to a “wet slide” as the season continues. He also commented on the increase in wind over the last month saying that, “if it keeps blowing like this, the hills will be unstable till spring!”
When asked about out-of-season factors for avalanches, specifically wildfires, Davidson said, “wildfires, and the damage they cause to a slope, are often overlooked, but are still key factors to our snow conditions.” He explained that fire changes how snow sticks to and is layered on a recently burned slope.
According to Davidson, the base layer of snow on a slope is anchored by vegetation that grows low along the ground. When a wildfire sweeps over a mountain, low-growing plant life and root structure will not regrow to anchor the snow in the same way it had in the past. This loss of soil stability creates a smoother ground surface that is less likely to hold the snow in place. Going beyond ground-level vegetation, the loss of trees and aerial coverage can also change a slope’s conditions. Slopes that have been burned, resulting in less tree coverage, are more exposed to wind and heat from the sun, creating a snowpack with more or different layers than in years past.
Davidson included examples of the 2020 Bridger Foothills fire and the 2017 Rice Ridge, both of which caused conditions to change on the slopes they burned through. He said both resulted in massive loss of tree coverage and the respective slopes saw a visible change in how sun and wind impacted slope construction and conditions.
As we move into the back half of our ski season, it is important to think about the changing snow conditions and avalanche danger in areas we enjoy, even though we may not have to worry about a forest fire in the dead of winter.