Turnagain Pass

There was a human triggered avalanche in the Tincan Library yesterday afternoon that caught two skiers and fully buried one of them. The fully buried individual was shallowly buried and able to dig themselves out. The second skier deployed their airbag and took a long ride with the avalanche but ended up on top of the debris. The avalanche was approximately 2′ deep and propagated across the gully feature that the group was skiing. We are still collecting information on this accident and want to extend our gratitude to the group involved who reached out to us to report the incident.

Otherwise we have not heard of any other large avalanches yesterday.

Photo of Tincan Library prior to the avalanche described above. You can see that even a small avalanche in this terrain can have high consequences. Photo 2.19.23 from Megan Guinn

Northwest outflow winds are expected to pick up during the day today with averages of 15-30 mph and stronger gusts. These winds will be transporting snow from a different direction than our last few easterly storms, which can make it difficult to read the wind loading patterns on the snow surface. This wind direction typically has the greatest impact along Turnagain Arm, Portage, Seattle Ridge, Crow Pass, and higher elevation ridgelines like Pastoral or Silvertip. Wind slabs 1-2′ deep are likely to be human triggered today, especially in those favored areas and along upper elevation ridgelines and cross loaded gullies. To identify terrain harboring wind slabs keep an eye out for active wind loading and step off the beaten track to check for firm or hollow feeling wind transported snow.

With mostly clear skies expected today the sun could also have an impact on the snow surface, especially in the afternoon when the solar intensity is highest. The winds might be enough to keep the snow surface cool, but in sheltered areas it is possible that sunny slopes could have natural loose snow avalanches and cornice fall is more likely with direct sunlight.

Active wind transport along the ridge of Pastoral yesterday. This will be more of a concern today as moderate to strong NW outflow winds impact the area. Photo 2.19.23 from Kit Barton & Sage Robine

We have a variety of potential weak layers in the snowpack right now which could produce larger and more connected avalanches. Within the upper 1-2′ of the snowpack there are several layers of buried surface hoar and facets that have developed between our recent storms. Over the past few days we have seen several avalanches that possibly involved one of these surface weak layers (Notch, Crow Creek, Tincan Library). The specific layers we are concerned about are the 2/5 storm interface, which is a 1.5-2.5′ deep layer of facets at upper elevations and a melt freeze crust with facets on top below 2000′, and the 2/15 surface hoar which was widespread in the forecast area before being buried 6-12″ deep. These weak layers may be more deeply buried in areas closer to Prince William Sound where there has been a lot more recent snowfall.

To determine whether these weak layers are an issue where you are travelling we recommend keeping a close eye out for any collapsing or shooting cracks, using small test slopes to check for unstable surface conditions, and digging hand pits or snow pits to look for the weak layers. Snow pits are the best way to test more deeply buried weak layers and get a sense of how sensitive they currently are. To avoid these avalanche problems you can always stick to lower angle terrain.

In addition to these weak layers in the upper snowpack there is also the 1/10 buried surface hoar that is closer to 2-4′ deep. This layer has been largely dormant for several weeks, but we continue to get unstable test results in isolated areas where the surface hoar layer is well preserved. This layer is unlikely to produce human triggered avalanches at this point in time, but if you find the wrong spot it could produce a very large avalanche. The likelihood is highest in areas with a thin overall snowpack like the southern end of Turnagain Pass and the Summit Lake area.

Example of the snowpack structure in Turnagain Pass with a variety of potential weak layers within the upper 3′. Photo 2.19.23 from Andy Moderow

In areas with a thin snowpack (i.e. Silvertip and the southern end of the forecast region to Summit Lake) there are various weak layers near the base of the snowpack that remain a concern. For these areas, triggering a larger avalanche is not totally out of the question and a more cautious mindset is recommended.