Turnagain Pass

A snowmachine triggered two avalanches in Main Bowl yesterday. Details are sparse, but the avalanches look to have failed on slopes that were loaded with snow and wind during the recent storm. Nobody was caught or buried in the avalanches.

Across the highway on Eddie’s Ridge, a skier triggered an avalanche about 80′ wide and 2.5-3′ deep, running about 120 vertical feet. As far as we know nobody was caught or carried in the avalanche.

Two Snowmachinie-triggered avalanches in Main Bowl yesterday (Feb. 10). Nobody was caught or buried. Photo shared by Joseph Fiskeaux on social media, 02.10.2024.

Skier-triggered avalanche on Eddie’s Ridge. Photo: Rafael Pease, 02.10.2024

The weak layer of snow that formed during January’s dry spell remains our main concern today. Friday’s storm brought 1.5 to 2.5″ snow water equivalent (SWE) to the area, which is adding a lot of stress to a layer that had already produced avalanches before it started snowing. We expect this layer to remain sensitive to human triggers today. It is now buried 2 to 3 feet deep on wind-sheltered slopes, and could be up to 3 to 5 feet deep or deeper on slopes that have been loaded by the strong winds we’ve seen over the past two days. Although the weather is supposed to be relatively quiet today, avalanche conditions remain dangerous.

These persistent weak layers are difficult to assess, and can give you misleading feedback prior to triggering a big avalanche. Some of the techniques we use to assess new snow problems (hand pits, slope tests, etc.) are usually not reliable for these persistent slab problems. Any signs like shooting cracks or collapsing are clear signs of dangerous conditions, but we might not always see these even when conditions are ripe for triggering an avalanche. Stability tests may be able to tell you a little bit more, but ultimately we already know there is a widespread weak layer that just got buried by a heavy storm, and we expect that setup to produce avalanches today. Rather than trying to assess our way into steeper terrain, we’re going to be giving this layer some time to heal and stick to lower-angle terrain for now.

This poor structure was already showing signs for concern prior to the storm that just added a whole lot of stress. There is now 1-2 feet of snow on top of the slab pictured above. 02.08.2024

Strong easterly winds throughout the most recent storm event have made another generation of wind slabs that we expect to remain reactive today. These will become larger and more likely to encounter as you gain elevation and get into the terrain that has been hit hardest by the wind. The most common features to find a reactive wind slab are steep slopes just below ridgelines, convex rolls, and steep gullies. These fresh wind slabs will feel stiffer on the surface, and you may notice a hollow, punchy feeling slab of snow if you hop off your snowmachine or step off the skin track and poke around. While wind slabs may sometimes be easier to manage than other avalanche problems, the deeper weak snow discussed in problem 1 above makes the wind slab problem a bit more severe today. A relatively small avalanche triggered near the surface has the potential to step down to that deeper weak layer, making a much bigger avalanche. This complicated combination of two different avalanche problems is a good reason to keep your terrain choices safe and simple for now.

Multiple natural wind slab avalanches in the alpine on Tincan Ridge seen yesterday. Photo: Tony Naciuk, 02.10.2024

It seems like the glide avalanche cycle that was producing large avalanches in December and January has slowed down for now. However, these avalanches are impossible to predict so we are not forgetting about the problem just yet. Avoid traveling under slopes with open glide cracks whenever possible, and be aware of the potential for falling into older glide cracks that are really difficult to identify now that they have been covered by the recent storms.