Turnagain Pass

• Wolverine – Andrew saw a couple large natural avalanches in a W facing bowl on Wolverine around 2500′ while driving down from the pass yesterday afternoon. Light was fading so he didn’t get a photo, but his best guess is that they were 3-4′ deep and the biggest one was 750′ wide. Due to limited visibility the last few days we have not been able to see much activity in upper elevations, so we don’t know how widespread this type of activity is.
• Tincan – Skier triggered pocket of storm slab at ~2000′ near Treeline. Avalanche was about 18″ deep and did not propagate very widely, skier was able to ride out of the avalanche.
• Front side of Seattle Ridge – Snowmachine triggered small storm slab at 1300′.

Small storm slab avalanche triggered by a snowmachine on 1.14.22 

It has been an active week for weather in the forecast area with 2-3′ of new snow in Turnagain Pass and 3-4′ in Girdwood over the course of the week. Strong east winds accompanied the recent snowfall and continued to transport snow at upper elevations with gusts up to 50 mph at ridgetops until yesterday afternoon. Cloud cover has obscured our ability to see recent avalanches at upper elevations all week, so we don’t have much information from above 2000′. We expect that the combination of lots of new snow and strong E winds have created large wind slabs 2-5′ deep at upper elevations which will be possible for a person to trigger.

Look for signs of recent wind transport on the snow surface, pillows of new snow on leeward aspects, and fresh cornices to identify wind loaded slopes. Due to the strength of the winds this week wind slabs could extend lower down onto a slope than normal. We recommend cautious route finding and assessing the snowpack and terrain carefully before exposing yourself to avalanche terrain today. Small test slopes are a very effective way to check how reactive wind slabs are before stepping into more consequential terrain. A few inches of new snow is supposed to fall with light winds today which could make identifying wind loaded areas much more difficult. If this is the case, feeling for hollow snow under your skis/board or sled track and stopping to dig hand pits or use a ski pole to test the surface layers of snow can be an effective way to identify wind loaded slopes.

Snowfall totals from this week have been variable across the forecast zone, with much higher totals observed in Girdwood compared to Turnagain Pass. We have no information from Placer and Portage but expect that they were on the high end of snowfall this week, with up to 4′ of new snow. If you venture into these areas today be aware that wind slabs could be on the deeper side of the 2-5′ range and that weak layers could be buried more deeply than we have seen in Turnagain Pass (see problem 2 for more details).

In addition to the wind slabs at upper elevations, there are a few potential persistent weak layers in the snowpack that have been showing signs of instability during our field tests this week. Both these layers are within the upper 3′ of the snowpack, but could be deeper in wind loaded areas, and are related to recently formed ice crusts. The most concerning layer is the New Years crust, which formed during a warm spell between Christmas and New Years and exists up to ~5000′ in elevation. Prior to the start of snowfall this week this layer had a mix of small facets and surface hoar on top of it which we expected would become a problem once a new load was applied to the snowpack. So far we have not observed widespread avalanche activity on this layer in the backcountry but have limited information due to lack of visibility. Yesterday at lower elevations on Tincan the New Years crust was buried about 2′ deep and showed signs of propagation potential in stability tests.

Another crust that exists between the two storm snow events from this week has been showing signs of propagation potential in some stability tests and is buried about 1-1.5′ deep at lower elevations. This crust formed at the end of the 1/10 snowfall event as wet snow fell up to about 2000′. The 1-2′ of new storm snow that fell on 1/13 has been showing signs that it is not bonding well with this icy surface and could be a weak layer for avalanches releasing underneath this most recent storm snow. We recommend evaluating the snowpack carefully before venturing into steep terrain today and being aware that the distribution of ice crusts varies with elevation, so it is important to assess the snowpack in an area that has similar aspect and elevation to where you want to enter avalanche terrain.

Stability tests showing propagation on ice crust underneath recent storm snow from front side of Seattle Ridge. Photo 1.14.22