Turnagain Pass

Despite the clearing skies, mild weather and fresh layer of new snow, approaching the mountains with extra caution is advised. Just before yesterday’s storm (more on that below), several slab avalanches were triggered that all failed in weak buried faceted snow 2-3′ below the surface. Some of these were very large and one, outside of our forecast zone sadly resulted in a fatality. These buried weak layers are now 2.5-4′ below the surface, depending on how much snow has fallen in what area. One thing we know for certain is these weak layers are a region-wide problem. How large the slab is above them and how likely the slab is for us to trigger, is the big question. The size of a potential avalanche is too big and the consequences are too high to forget we have these dragons lurking below. Hence, we need to be on our guard during this clear sky period regardless of where we travel. Sticking to lower angle terrain with nothing steep above you is a good way to manage this issue and have a safe day out in the backcountry.

Things to keep in mind with this Persistent Slab problem:

• Just because the surface snow ‘seems’ or ‘feels’ solid doesn’t mean the buried weak layers are
• No signs of instability may be present before a slope releases
• It could be the 2nd or 10th person on a slope before someone finds the trigger spot
• Large slabs could be triggered remotely: from the bottom of the slope, the top or to the side of the slope.

A cross section of the snowpack at 1,900′ showing facets and a crust 28″ (70cm) below the surface. This is just one of several weak layers that are causing so much grief in the snowpack structure.

Storm snow instabilities associated with yesterday’s new snow are something to keep your eye on. These include: wind slabs, storm slabs and loose snow avalanches. With such poor visibility yesterday, we have yet to get a handle on the natural avalanche activity that occurred during the storm. That said, reports from Sunburst point to the new snow beginning to bond, yet lower layers in the snowpack were showing some signs of reactivity.

Storm total (Tuesday night through Thursday morning):

Turnagain Pass:  16-18″ snow (1.3″ water equivalent)
Girdwood:  10-12″ snow (0.8″ water equivalent)
Summit lake:   5-7″ snow (0.4″ water equivalent)

Wind slabs are the most likely storm snow instability to be seen and the slowest to bond. In areas that saw wind loading from the strong easterly winds, these wind slabs (1-2′ thick) could still be touchy. Feel for stiff snow over softer snow and look for cracking in the snow around you. Soft storm slabs (around 1 foot thick) in areas out of the wind effect may also still be possible to trigger. Again, watch for signs of cracking in the new snow. Performing quick hand pits are good ways to see how the new snow is bonding with the older snow surface. On steep slopes, loose snow avalanches (sluffs) may be easy to trigger. Remember, avalanches in the storm snow could step down and trigger large slab as mentioned above.

Cornices:  These have grown over the past 36 hours and we can’t forget to give them a wide berth from above and limit time under them from below.

Very limited visibility was over the area yesterday. This photo is from Sunburst at Turnagain Pass.