Turnagain Pass

The storm impacting the area over the past 24 hours is following a familiar pattern, with underwhelming snowfall amounts in Turnagain Pass (2-4″), higher amounts in Girdwood (3-6″), and higher again in Portage and Placer (6-9″). Light to moderate snow is forecast to continue throughout the day today and should add another 1-2″ in Turnagain Pass and Girdwood and 3-6″ in Portage and Placer.  The winds have tapered off to 10-20 mph after strong gusts yesterday morning in the 30-50 mph range. Wind slabs at upper elevations are the primary avalanche problem today in areas that receive less than 9-12″ of storm snow. Wind slabs are possible for a person to trigger but unlikely for natural triggering now that the wind speeds have backed off. If you see active wind loading in the area you are travelling then natural avalanches are possible and you should be aware of overhead avalanche terrain.

In coastal areas that have received significantly higher snow totals and will continue to get new snow today there is the potential for storm slab avalanches in protected areas. A layer of surface hoar buried underneath the new snow could make those storm slabs easier to trigger and propagate more widely than typical. Keep an eye out for shooting cracks or collapsing (whumphs) and use test slopes to determine whether the new snow is bonding well to the old snow surface. On Tincan yesterday, the new snow was shearing off easily in hand pits on top of the upper layer of buried surface hoar but there was only about 4″ of new snow which was not enough to create storm slab conditions.

Glide Avalanches: Glide cracks have opened up across the forecast area including near the Seattle Ridge uptrack and on the south faces of Eddies and Tincan. With continued warm temperatures these cracks could potentially release, causing a very large and destructive avalanche. Minimize time spent underneath them to limit your exposure to this hazard.

Loose Avalanches: Both dry and wet loose avalanches are likely with the new snowfall. On southern aspects the combination of warm temperatures and sun was creating moist snow at the surface yesterday which could create wet loose avalanches on steeper terrain. On northern aspect dry loose avalanches are likely in the new snow on steeper terrain.

Small wind slabs naturally triggered by wind loading yesterday at 2300′ on the lower end of CFR on Tincan Common. Photo 3.16.22

Broken cloud cover interspersed with periods of obscured clouds and light snow in Turnagain Pass yesterday. Photo 3.16.22

A layer of buried surface hoar and near surface facets from 3/2 have been responsible for several human triggered avalanches in the forecast area and could become more active again with a fresh load of new snow. It can be difficult to spot this layer in a snowpit and performing an instability test, like an extended column test or compression test, can help identify the layer and give you a sense of how reactive it is in the area you are travelling. On Tincan yesterday, we found the 3/2 buried surface hoar down 16-20″ from the surface and had no propagation in our instability tests on the layer with consistently hard results in terms of number of taps to initiate the layer (ECT N 23, 26). In my pit there was a notable collapse in the weak layer when it failed in the ECT, which is a common characteristic of buried surface hoar. The distribution of this layer is variable but it seems to be most prevalent in Turnagain Pass, both on the skiers side and along Seattle Ridge.

Snowpit structure from 2400′ on NW aspect of Tincan. Photo 3.16.22