Turnagain Pass

Turnagain Pass

• Pete’s North – Two skier triggered avalanches on a layer of buried surface hoar from 3.16 about 12-16″ deep and 75-100′ wide. The first avalanche was triggered as we were preparing to dig snowpits in a forested clearing on relatively low slope angles. The second was intentionally triggered on our descent in a slightly more open area adjacent to the first avalanche. The buried surface hoar was 3-6 mm grain size and very thick on this relatively protected slope near the top of treeline (see on here for more details).

Skier triggered D 1.5 on a layer of buried surface hoar from 3.16. Avalanche triggered while preparing to dig snowpits in a forested clearing at 2000′ on a W aspect of Pete’s N. Photo 3.23.22

Skier triggered D2 soft slab on a layer of buried surface hoar from 3.16, on a W aspect at 2000′ on Pete’s N in Turnagain Pass. Photo 3.23.22 

• Tincan – Small storm slabs 8-10″ deep on steep rollover in Tincan trees. The new snow fell on top of surface hoar that was buried on 3.22 which is making storm slab more reactive than typical and possible to trigger on lower slope angles.

Small storm slabs in the 8-10″ of new snow that had fallen as of yesterday afternoon. Photo from Brooke Edwards 3.23.22

A powerful storm is impacting our area and has already deposited 10-16″ of snow, with another 30+” of snow possible in the next 24 hours. Strong winds averaging 25-50 mph with gusts up to 100 mph will accompany the snowfall and have been actively transporting snow into fresh wind slabs at upper elevations since yesterday morning. This is a massive load on top of a snowpack that contains three layers of buried surface hoar within the upper 2-3′ of the snowpack. Human triggered avalanches are very likely and natural avalanches are likely, and could step down to deeper weak layers to create very large avalanches (see problem 2 for more information). Travel in avalanche terrain is not recommended, including travelling on or underneath all slopes with 30 degree or higher slope angles. Avalanches from upper elevations could runout to valley bottoms so avoid travelling underneath any potential avalanche terrain.

The new snowfall will make storm slab avalanches in protected areas very likely for human triggering, especially since a layer of buried surface hoar exists just beneath the new snow which was buried on 3.22. In addition, wind slabs up to 2+’ deep are almost certain to be triggered in treeline and alpine elevation bands. We need to step back and give the mountains some breathing room as this storm impacts our region.

Active wind loading in treeline and alpine elevation bands throughout the day yesterday. Photo 3.23.22

There are three separate layers of buried surface hoar in our upper snowpack that have been responsible for numerous human triggered avalanches in the past few weeks. These layers were buried on 3.2, 3.16, and 3.22 respectively. The distribution is widespread in the Turnagain Pass and Seattle Ridge area including upper elevations. The weak layers have also been observed in Portage/Placer and Girdwood, but the distribution seems to be a little bit less widespread. Locating these layers of buried surface hoar can be tricky in a snowpit if they are not particularly well preserved. However, that does not mean you could not trigger an avalanche on these layers. Over the past two weeks many very experienced parties have been involved with human triggered avalanches on these weak layers which should be a reminder to give these weak layers a wide berth by sticking to lower angle terrain. With a massive new load of snow coming today it is likely that these older weak layers will reactivate and create very large avalanches up to 3+’ deep.

Yesterday on Pete’s N we triggered an avalanche on the 3.16 buried surface hoar while preparing to dig snowpits and evaluate stability. The avalanche propagated very widely and released the entire area of steeper terrain within a small opening in the trees. In our crown profile we found all three layers of buried surface hoar in the pit wall but only had propagating ECT results on the 3.16 layer that was also the weak layer for the avalanche. On our descent we were able to trigger another avalanche on the same layer on a similar feature that was in slightly more open terrain (see ob here). We recommend avoiding all avalanche terrain during the period of intense snowfall over the next 24-48 hours.

Buried surface hoar on the bed surface of a D 1.5 avalanche we triggered while preparing to dig snowpits at 2000′ on a W aspect of Pete’s N. Photo 3.23.22