Galena Summit & Eastern Mtns

You could trigger slab avalanches today, most likely where the wind has drifted recent snowfall. Picture where an avalanche would carry you—through trees, into creeks, etc—before skiing or riding steep slopes. You may be able to trigger avalanches remotely—from gentle or flat terrain above, below, or to the sides of steep slopes. 

How will the ugly layer of surface hoar buried 1-2 feet deep throughout the majority of the forecast area react to the 2-10” of snow that fell the past couple days? I’d love to give you a clear, one-sentence answer to that million-dollar question; sorry, but it’s not happening. 

Yesterday, I checked out the snowpack in the terrain just out of bounds on the north side of the Sun Valley Ski Area on Bald Mountain. The pretty grey stripe of surface hoar was there, a little over a foot down. It reacted poorly to snow stability tests, giving me results that screamed: “do not ski steep slopes with this snowpack setup.” While I was working, two younger skiers center punched the starting zone of an avalanche path where a serious injury occurred about 5 years ago. Skiing two at a time, no rescue gear. I immediately got nervous, worried about what would happen as they dropped over the rollover. I quickly filled in my pit, put my tools away, and headed over to get a look into the avalanche path they skied. Nothing, just two nice sets of tracks.

This story leads to two questions: 

1. Why are we getting mixed signals from the snowpack?
2. How do we make “good” decisions in times like this? 

The mixed signals question: Unfortunately, that is how persistent weak layers tend to behave. On Sunday, Sun Valley Heli Ski staff and guests skied great snow on several slopes without issue. However, the staff was still quite concerned about the buried surface hoar layer. They verified their concern when they triggered a sizable avalanche while testing the top of a slope. This avalanche failed on an E-NE facing slope at 8,600’. Although the angle of the path that failed was in the low 30 degree range, the slab pulled back into terrain above a rollover that was only 26 degrees. Recent winds had loaded this slope, increasing the stress on the weak layers in the snowpack. I also experienced the mixed signals yesterday when the two skiers in the Baldy sidecountry/out-of-bounds skied a slope without issue, even though my evaluation was clearly showing unstable conditions in wind-affected terrain. 

How to make “good” decisions: Both the Sun Valley Heli Ski and Baldy stories demonstrate the brutal feedback environment we’re currently facing. You can ski or ride many steep slopes without triggering an avalanche, but you could find the right spot to trigger a slide—possibly when you least expect it. One good way to mitigate your risk in times like this is to focus on the consequences of getting caught in a slide. It’s very difficult to accurately forecast whether a given slope will slide, but it’s simple to picture what will happen to you if it does slide. You can steer clear of avalanche paths that would drag you through trees, deposit you in creeks or terrain traps, or carry you over cliffs or into scree fields. 

Putting the bow on the Christmas present: we're going to be stuck with the surface hoar layer concerns for at least another storm cycle. We'll probably continue to experience obvious signs of instability like collapsing and cracking, people will ride and ski many avalanche-prone slopes without any issues, and we will likely receive reports of occasional human-triggered avalanches in the coming days. Since accurately predicting whether you will trigger a given slope is currently next to impossible (where the surface hoar is present), consider factoring the consequences of an avalanche more into your decision-making than usual.