Turnagain Pass

No recent avalanches were reported yesterday. We saw some older loose snow avalanches that were able to build up quite a bit of volume in steeper terrain on Tincan Proper and the Library. The last known avalanche on the 1/10 buried surface hoar was on Sunday Jan 22nd. The last known avalanche on the Thanksgiving facet/crust layer was on Saturday Jan 7th.

Loose snow avalanches that built up pretty large debris piles on the steep S face of Tincan Proper. Photo 1.27.23

It has been almost a week since the last known avalanche was triggered on the 1/10 buried surface hoar layer. This layer has caused a ton of human triggered and natural avalanches since it was buried and is widespread across the forecast area. It is encouraging that we are starting to see this layer gain strength and be less reactive in snow pit tests, but the potential for triggering an avalanche on it still exists above 2000′ and could result in a large 1-3′ deep avalanche with wide propagation. Based on the tracks in Turnagain Pass it looks like most folks have been keeping their terrain conservative over the past week, which is great, but also means we have limited information on how reactive this weak layer is. Due to the potential consequences of triggering an avalanche on this weak layer we are taking a very gradual approach to assessing it and just starting to tip toe into low angle alpine terrain.

To avoid this avalanche problem we recommend sticking to low angle slopes and being aware of the potential for remote triggering an avalanche onto adjacent steeper terrain. Any signs of collapsing or shooting cracks are a strong indication that the weak layer is still reactive in the area you are travelling, which is what Andrew found in upper Lynx Creek on Thursday. Snow pit tests, like a compression test or extended column test, are a good way to identify and test the weak layer. The unusually warm temperatures at upper elevations today could cause this layer to become more reactive, but there is a lot of uncertainty about whether the warm weather will make triggering an avalanche more likely.

Lingering wind slabs, loose snow avalanches (aka sluffs), and cornice fall are all additional concerns at upper elevations today. The combination of warm temperatures and hopefully sunshine will make loose snow avalanches and cornice fall more likely. Cornices have been steadily growing and are quite large along many upper elevation ridgelines. Be aware of the potential for cornice fall if you are travelling underneath a cornice receiving direct sun. Glide avalanches were observed in the Summit Lake area recently and the warm temperatures and sunshine could make them more likely to start popping up in our forecast area as well.

All our weak layers still exist in the snowpack but are gradually becoming less reactive in snow pit tests. Photo 1.27.23

Yup, very large avalanches 4-8′ deep on a layer of facets around the Thanksgiving crust are still the worst case scenario for our snowpack. At upper elevations on Sunburst yesterday this weak layer and crust combination was still very prominent in the snowpack and our snow pit tests indicate that it can still propagate to cause a very large avalanche. However, we had to hunt to find a thin area where we could dig down to this layer and the snowpack on top of the weak layer was very strong even in this thin spot. The most likely place to trigger an avalanche on this weak layer is from a thin spot in the snowpack, like where wind has scoured away most of the snow or where rocky outcrops are sticking through the snowpack. The above freezing temps at upper elevations today could cause this layer to be more sensitive.