Turnagain Pass

Solar radiation from yesterday’s sunshine initiated many wet loose avalanches on steep southerly facing terrain. These all appeared to be composed of Thursday’s 6-8″ of new snow. Human triggered sluffs on shaded aspects also were very common yesterday along with a few sluffs that pulled out small shallow storm snow slabs and one small human triggered slab. There were 2 larger avalanche events:

Tri Tip (NW aspect at 2,700′):  In the Summit Lake area there was a close call with a skier caught in a slab avalanche up to 20″ deep and 100′ wide. The skier was ascending when the slab released 50′ above them. The skier tried skinning out of the way and was able to remove one ski before being caught and carried for 250′. The skier was partially buried with head above the snow and uninjured. Thank you to the group for sharing their experience and we are very thankful everyone is OK. Please take a minute to read their report HERE.

Raggedtop (NE aspect 3,600′):  Natural avalanches were noted in the NE bowl of Raggedtop yesterday. One large avalanche appeared to be fresh and may have released yesterday morning with early sunshine triggering a loose snow avalanche off the rocks, which triggered a slab avalanche lower on the slope, and then stepped down to buried weak layers and triggered larger slabs. See photos below in Problem #2.

Skier triggered avalanche on Tri Tip, 2,700′ on a NW aspect in the Summit Lake area. Photo taken 3.26.21 by Mike Davidson from the highway below.

Closer view of Tri Tip avalanche taken from the party involved. 3.26.21.

Natural sluffs that occurred during Thursday’s new snow can be seen in the middle of the photo. Also note the small slab that released mid-slope in the shade by a skier. Skier was able to easily ski off the slab. 3.26.21 Ryan Smeeding.

Another northwest wind event is on the horizon. As has been the case this season, these winds are likely to impact areas south of Turnagain Pass the most, but looking at the models, Turnagain may not get so lucky this time. Expect the winds to be on the rise through the day and by 6pm could be averaging 25-30mph along the ridgelines at Turnagain Pass. This flow direction often channels through Turnagain from the south along the non-motorized ridges while it remains westerly along Seattle Ridge. The bottom line however is wind slabs are likely to form on a variety of aspects later today.

There is plenty of soft surface snow to blow around, especially on the shady aspects that were not hit by the sun yesterday. Any new slabs could be quite touchy and up to a foot thick or thicker in areas with sustained winds for several hours. How quickly the wind will start forming slabs is a bit of a question, but I’d bet by the early afternoon; especially in the Summit Lake area.

Watch for active wind loading, which should be easy today, and avoid any slope or cross-loaded gully with fresh wind deposited snow. Shooting cracks will be good clues as well as signs of stiffer snow over softer snow. New wind loading could also overload buried weak layers and create a larger avalanche, similar to the avalanche triggered yesterday in the Summit Lake area. Although sun crusts are likely to be found on southerly slopes, winds could still be strong enough to load these aspects.

Forecast NW winds around 3,000′ today at 6pm. Wind speeds are represented by colors. This is Windy.com’s display of the NAM (North American Mesoscale) weather modeled winds.

There is still a concern of finding a slope where old buried weak layers (facets and buried surface hoar) are still reactive. The natural avalanches on Raggedtop and the skier triggered slab on Tri Tip are unfortunately good examples of what we are talking about. These slabs appear to have all or parts of the avalanches breaking deeper into old weak layers. Girdwood Valley and Summit Lake seem to be the two places most suspect for this type of avalanche.

After some new snow on Thursday and winds today adding stress to these layers, there is still a possibility a person could trigger one of these persistent slab avalanches. Be on the lookout for areas that were previously wind loaded and those with any new wind loading. The most suspect terrain will likely be at upper and mid elevations, especially immediately below ridgelines, in cross-loaded gullies, and below convexities. As always, watch for signs of instability, use good travel protocol, and think about terrain consequences. This type of avalanche issue might allow you to get well out on the slope before the avalanche releases and it might not be the first person that triggers the avalanche.

Raggedtop natural avalanche. Note the point release sluffs off the rocks that in turn triggered several slabs, some of which look to have stepped down to old buried weak layers. 3.26.21 Ryan Smeeding.

Wider view of avalanche and debris. 3.26.21 Ryan Smeeding.