Turnagain Pass

No recent avalanches were observed yesterday due to very poor visibility. The last known cycle of avalanche activity was during and after the Easter storm when storm slabs and loose snow avalanches were occurring because the new snow did not bond well with the icy old snow surface.

Temperatures are expected to increase today, reaching close to freezing at upper elevations, which will cause the new snow from yesterday to start shedding off of steeper slopes later in the day. Loose wet avalanches are typically small, but on larger steep slopes they can entrain a lot of loose snow on their way down and produce enough debris to potentially bury a person. We saw lots of avalanche activity like this after the Easter storm and expect very similar conditions today. This type of avalanche activity typically starts in the early afternoon and can increase in size into the evening as more of the surface snow melts and becomes weak enough to slide off the mountainside.

These conditions develop throughout the day as the snow surface gradually melts. You can monitor conditions by paying attention to how deeply your skis or snowmachine are sinking into the surface snow and looking for roller balls or smaller wet loose avalanches. If your boots are sinking into wet snow over ankle deep that is a sign that larger wet loose avalanches are likely. Moving to higher elevations or a shadier aspect where the surface snow is less melted is recommended to avoid this hazard, but temperatures are going to be warm enough today that we expect loose wet avalanches on all aspects.

Lingering wind slabs around 1′ deep that formed yesterday could also be an issue along upper elevation ridgelines. To identify wind slabs look for areas with hollow feeling wind transported snow on the surface and use small test slopes to check for shooting cracks. In addition, cornices and glide cracks are more likely to fail during period of warmer temperatures especially if cornices are getting direct sunlight. This is the time of year when these behemoths start to naturally release and you definitely want to avoid being underneath when a big chunk falls off!

Examples of long running wet loose avalanches in Todd’s bowl on the N aspect of Tincan. Photo 4.13.23

A weak layer of facets buried about 3-6′ deep in the snowpack is still on our radar due to widespread very large avalanche activity on this layer in the second half of March. It has been two weeks since we have seen any avalanche activity on this layer and we think it is very unlikely for a human triggered or natural avalanche. However, due to the consequences of being involved with an avalanche this size we are still keeping track of it.

As the temperatures increase and more free water exists in the snowpack we expect that this weak layer could become active again and produce large wet slab avalanches.  The image below shows how melt water is percolating through the snowpack, with darker colors indicate melt water pooling in that layer. The 3.14 facet layer is indicated with a red popsicle stick and we can see a lot of melt water pooling in that layer, which is an early indication that this layer could be problematic as more melt water moves through the snowpack over the coming days or weeks.

Results of a percolation test from Tincan yesterday, with an alarming amount of the melt water pooling in the 3.14 facet layer. Photo Nancy Pfeiffer 4.14.23

Overview of general snowpack structure. The depth to the weak layer varies a lot across the forecast area from 3-6’+ deep. Photo 4.13.23