Turnagain Pass

With a long weekend beginning today and many folks looking forward to enjoying the high quality snow from last week’s Valentine’s Day Storm, it may be easy to forget there is a bad layer of snow just 2-3′ below the surface. This is a thin layer of buried surface hoar and near surface facets (seen in the video and photo below) that sit under the 2-3+’ of snow from last week. Observations from yesterday continue to confirm that the layer is very reactive and triggering a slab avalanche on the steeper slopes is likely. On Wednesday, there were several remotely triggered slabs on this layer in the Girdwood Valley. At Turnagain Pass, very few folks have been out to test the slopes. Visibility should be good enough today, and this weekend, for travel to the upper elevations. If this is the case, remember the snowpack is unstable. This could be a tricky situation since the pack may ‘seem like it feels fine’ and people could get away with riding/skiing steeper terrain before a slope breaks. Slopes that saw higher traffic last weekend could remain intact while an adjacent slope slides. 

What to keep in mind if headed to the mountains:

1. These slabs can be triggered remotely, from the ridge, the side or below
2. In terrain that saw high traffic last weekend, this layer will likely be more stubborn to trigger, but don’t let that lure you into thinking the pack has stabilized
3. No obvious signs on instability, or red flags, may be present before a slab is triggered
4. This is the kind of avalanche that could have several tracks on the slope before someone finds the right trigger point (thin areas of the slab). 

What can we do? Terrain management is the key for hedging our bets. This is simply sticking to lower angle slopes, under 35 degrees with nothing steeper above you.

If you did not see this video yesterday, take a look today. 

Solar effects from SUNSHINE??

If the sun shines and winds are calm, solar radiation can be significant this time of year. Wet/damp loose sluffs on steep South aspects are likely when we do get this first shot of warmth. Additionally, the warming surface snow can enhance the likelihood of triggering a slab. Avoiding sun baked slopes this weekend will be recommended. These Southerly aspects likely have a crust under the new storm snow with either buried surface hoar or near surface facets on top – creating a perfect slab/weak layer/bed surface set up.

Cornices have grown and changed shape following the Valentine’s Storm. These could be teetering on the balance and could break further back than expected. If one does fall it is likely to trigger a slab avalanche below, potentially creating a very dangerous situation if a person is involved. If the sun comes out today, or this weekend, warming can loosen these beasts and increase the potential for them to break.

Lurking at the bottom of the snowpack are various layers of facets with varying degrees of strength. In the Summit Lake zone and some areas in Girdwood Valley and Johnson Pass depth hoar has been found. Last week’s storm cycle tested these layers and only a few avalanches, that we know of, broke in the deeper layers (Girdwood Valley, Portage Valley and Summit Lake). These layers will be tough for people to trigger, but possible in shallow snowpack zones. More likely is the case where an avalanche occurring in the upper layers of the pack will have the potential to step down and release the entire snowpack. If this does happen the volume will be large and could run long distances. The possibility of these large avalanches is another reason for conservative terrain choices.