Turnagain Pass

• Magnum – A large cornice fall in PMS bowl at 3400′ on the SW aspect of Magnum triggered a large avalanche on the slope below. Luckily, as far as we know, no one was travelling in the area and caught in the avalanche. You can see the gouge marks left by the cornice in the bed surface below, this is a very large trigger that appears to have released an avalanche on one of our deeper weak layers.

Cornice fall triggering a large slab avalanche that ran to the valley bottom on PMS bowl on Magnum. Photo Kellie Okonek 3.30.22

• Seattle Ridge – A glide crack released just south of the moto uptrack yesterday sometime while we were riding up on Seattle Ridge. This glide release was relatively small, but it still created a large debris pile and released down to the ground.

Glide avalanche on SE aspect at about 2000′ that released during the day yesterday. Photo 3.30.22

• Wet loose – Lots of wet loose avalanches on east, south, and west aspects yesterday, including some from within the past two days that triggered a slab avalanche on their way down (see ob here).

Wet loose avalanches on S face of Wolverine with a few larger debris piles that likely caused a slab avalanche to release on their way down. Photo 3.30.22

After a beautiful and clear day in the mountains yesterday we are transitioning back to stormier weather today, with snow showers possible and increasing wind. The wind is coming ahead of the precipitation for this storm which could be exactly what we need to help knock down a new layer of surface hoar that formed on top of a thin melt freeze crust above 1500′ in Turnagain Pass. Wind speeds are expected to be 15-30 mph today with gusts possible up to 50 mph. We observed that thin, breakable melt freeze crust on all aspects up to our high point at 3000′ yesterday which should limit the amount of snow available for transport. Somehow the wind always seems to find snow to move around, so wind slabs up to a foot deep are still the most likely avalanche to trigger today. Human triggered wind slabs are likely and natural triggered wind slabs are possible.

Wind slabs are most likely to be found at upper elevations along ridgelines, cross loaded gullies, and convex rolls. Keep an eye out for shooting cracks or hollow feeling pillows of snow to identify areas with fresh wind slabs. With a new layer of buried surface hoar and facets potentially underneath these wind slabs they could be easier to trigger than normal, release on lower angle slopes, and propagate widely. The bigger concern from a risk management perspective is the potential for triggering a very large avalanche on a deeply buried persistent weak layer, see problem 2 for that discussion.

Cornice: The recent cornice fall in PMS bowl on Magnum is a good reminder of the hazard that cornices can pose, especially on days where they are getting intense solar heating. Today might not have a ton of sunshine, but with moderate winds cornices will be building again and could release more easily where new snow has been added.

Glide: A glide avalanche released along Seattle Ridge yesterday, just south of the moto up track. We have received many observations of glide cracks opening up across the area and they are becoming more active as we move towards the spring. Try to avoid spending time underneath glides as they can release without warning and create large destructive avalanches.

New batch of surface hoar and surface facets above a thin, breakable melt freeze crust which we observed from roughly 1500′ up to our high point of 3000′. Photo 3.30.22

It is still possible to trigger a very large and destructive avalanche on a deeper weak layer. However, with the weak layers buried 3-6′ deep in Turnagain Pass underneath very strong and supportable snow from the past two storms the chances of finding the trigger location are getting lower. In our snowpit yesterday at 2000′ on a north aspect in main bowl off Seattle Ridge we were able to find the 3/22 and 3/16 buried surface hoar layers within the top 5′ of the snowpack. They did not show any signs of instability in our tests, but we don’t really expect them to now that they are buried so deeply. This is the trickiest part about deep persistent slabs, they tend to show no signs of instability until a trigger hits the sweet spot and they create a huge avalanche.

Unfortunately, that means we are stuck grappling with the question of how much are we willing to expose ourselves to this low likelihood but high consequence hazard. If you decide to venture into steep terrain make sure to follow safe travel protocols: only expose 1 person in avalanche terrain at a time, stop and group up in safe zones outside the runout, always spot your partners. Avoiding this issue is pretty simple, just stick to terrain less than 30 degrees and be aware of overhead hazards because there is the potential for remote triggering. Personally, after triggering two avalanches on the 3/16 buried surface hoar last week on Pete’s North, I am going to keep it conservative for awhile longer and let the snowpack have some extra time to bury those layers even deeper.

Snowpack structure from our pit in Main Bowl. Overall the upper snowpack is strong, but those buried persistent weak layers make for very concerning structure 3-6′ down. Photo 3.30.22