Turnagain Pass

There were no recent avalanches observed or reported yesterday. We had good visibility for the first part of the day and saw evidence of recent wind transport on ridgelines but no fresh avalanches. The last known avalanche activity was a human triggered persistent slab in the Tincan Library which caught and carried two skiers last Sunday. See report here for more details.

This weekend looks like it will be cold with mostly clear skies and moderate NW outflow winds. We are expecting winds to reach 20-30 mph in areas that are favored by this NW wind direction like Turnagain Arm, Crow Pass, Portage, Seattle Ridge, and upper elevation ridgelines. Human triggered avalanches up to 1′ deep are likely in areas experiencing active wind loading. To identify areas harboring wind slabs you can look for signs of wind transport on the snow surface, step off the beaten path to feel for firm or hollow wind drifted snow, and use small test slopes to check for shooting cracks. To avoid this problem you can stick to treeline and below treeline areas which should be largely sheltered and are holding good snow conditions thanks to the last few cold storms.

Even though temperatures were cool with light winds yesterday we still saw sun crusts forming just underneath the surface on steeper south facing terrain features. This is not concerning from an avalanche perspective right now but is worth noting that snow conditions will become more aspect dependent moving forward. In areas with soft snow still on the surface and steeper terrain loose snow avalanches are possible today. Cornice fall is also more likely with sun shining so it is worthwhile to be aware of any large cornices overhead.

For the past week or so the persistent weak layers in the upper snowpack have been sending mixed signals. Other than the avalanche in the Tincan Library we do not know of any recent avalanche activity in the area and it seems like folks have been travelling all over the place. In our snow pit tests we have seen a few concerning results where the weak layer has shown the potential to propagate across the slope and create a larger avalanche, but we have also had a bunch of tests where these layers have not shown concerning results. This leaves us in a tricky place as far as deciding whether or not to be concerned about these weak layers.

On the one side, the presence of these weak layers in the upper snowpack and the few signs we have seen that they have the potential to produce larger avalanches could be enough to justify sticking to lower angle terrain. On the other side, the lack of recent avalanche activity is a strong sign that these weak layers might not be an issue until the next time we get a loading event. That new loading event could be today in areas getting wind loading, but in sheltered areas we will have to wait until the next storm to test whether these persistent weak layers will become more active. For now we continue to consider it possible for human triggered avalanches 1-3′ deep on these persistent weak layers, but with no new snow expected over the next few days the likelihood of triggering should be trending towards unlikely.

One of the persistent weak layers (2/5 facets) in the upper snowpack which failed in one extended column test and propagated across the column. Photo 2.24.23

Snowpack structure in treeline elevation band on S aspect of Tincan, concerning test result is highlighted in red but other test results are not very concerning. Photo 2.24.23

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.