Turnagain Pass

We heard of one skier triggered slab avalanche yesterday. This was on Eddie’s Ridge. A skier reported to have triggered the slab on a lower SW facing steep roll, around 1,600′, and was able to ski off the slab. No photos or additional details. It’s most likely the avalanche failed around 16-20″ deep at the new/old snow interface from Feb 5th (12-18″ of snow fell on Feb 5 and 6). At these lower elevations a crust exists under this interface, which could be keeping that old storm snow from bonding in places.

As noted by the skier triggered avalanche yesterday on Eddies, there is still some funny business under the storm snow from last Sunday/Monday. With 4-6″ of new snow and light winds over the past 30 hours, the main concern will lie with this older storm interface. In general the Feb 5/6 storm snow has shown mostly signs of stabilizing, but not everywhere. At elevations below 2,000′ the storm snow fell on a layer of weak snow sitting on a crust that was formed in late January. This lower elevation setup is something to have on our radar as even a small slope could pop out and cause harm. These slabs are in the 1-2′ deep range and something we can look for with quick hand pits.

At the higher elevations there also could still be some slopes harboring surprises. These will most likely be associated with wind slabs (below in Problem 2), but other factors could be present. The sun created a crust on certain steep southerly slopes last week. New snow sitting on these crusts could be suspect for sliding. Once the skies clear enough for travel into the Alpine, we’ll need to be watching for all the red flags.

Another layer that we are still thinking about is the old 1/10 buried surface hoar that is 2-4′ deep in the snowpack. This layer has not caused an avalanche for 2.5 weeks and it’s not likely to cause one today. Yet, it’s good to know that layer is still under our feet, it can be quite easy to see in snow pits, and just more encouragement to always keep with our safe travel protocol.

New layers of surface hoar have been forming during short clear spells over the past week. One was on Saturday Feb 4th, another on Tuesday, Feb 7th, and this one photographed by Allen Dahl is from Thursday, Feb 9th. These layers are intermixed with new snow in the top foot of the snowpack and may not end up being a concern, but we’ll be looking for them just in case. 

Two days ago, on Friday, the region saw strong easterly winds. Since then the visibility has not been good enough to travel into the Alpine or even see into these upper elevations as to what the winds did and any avalanche activity associated with them. However, once the sky does clear, know that lingering wind slabs could be hiding under several inches of new snow that has been tricking in since the winds stopped.

Wind slabs could be sitting on various layers, one of which could be buried surface hoar and slabs may not be all that well bonded. They are likely to be in the 1-2′ deep range and along ridgelines and in cross-loaded gullies. As always, paying attention to areas winds have loaded slopes, feeling for stiffer snow over softer snow, and looking for cracking or collapsing in the snow under your feet/machine are key red flags.

Loose Snow Avalanches:  Sluffs are likely to be triggered on steep slopes due to several inches of new light snow on the surface.

In areas with a thin overall snowpack, such as Silvertip and south of Turnagain Pass, there are deeper weak layers near the base of the snowpack that are concerning. The most widespread weak layer is the Thanksgiving facet/crust combo but in some areas (Summit Lake for example) there is also a weak layer of basal facets. Triggering a large avalanche breaking in these layers is not necessarily likely, but also not out of the question. Additionally anytime we see active weather, it is possible they could become more reactive and catch us off guard.