Turnagain Pass

After 8 days in a row of human-triggered avalanches failing on a layer of buried surface hoar, we finally got one day with no reported avalanches.

The weather is picking up, and it is going to make avalanche conditions more dangerous today. Winds have been ramping up since just after sunset last night, and are expected to blow 25-35 mph with gusts of 30-45 through today into tonight. These winds will be building touchy wind slabs, which will be an ever bigger problem than normal because they are forming on top of a snowpack with a reactive weak layer buried 2′ deep on average.

We can expect to see some avalanche activity today as the winds continue to ramp up. While the most dangerous slopes will be those getting loaded today, it is important to remember that the layer of buried surface hoar we are dealing with is likely to produce avalanches in sheltered terrain as well. We’ve seen avalanches triggered remotely on this layer (detail from my field day at Tincan two days ago), which means you can trigger an avalanche from low-angle terrain below or adjacent to steeper slopes. As the layer gets buried deeper, it is becoming more difficult to assess with common travel tests like hand pits and test slopes. It is also giving fewer warning signs like shooting cracks or collapses before producing big avalanches. With how widespread the layer is, we don’t need to rely on these travel tests to know that we’re traveling on a dangerous setup. The best option for now is to assume you are traveling over a dangerous snowpack with a weak layer that is waiting for a trigger. The tricky snowpack actually makes travel advice kind of easy- put the big (or even medium) objectives on hold for now, stick to low-angle terrain, and avoid spending any time under steep slopes.

Cornice fall: Strong winds will continue to build large cornices today, and it is likely we will see some natural cornice failures. These cornices could likely trigger avalanches on steep slopes below. They may be hard to spot from a distance if visibility is limited today, but this is another reason to avoid spending time below steep slopes.

Could you find this layer in a hand pit? It’s 2 feet deep and becoming harder to detect, but still producing avalanches. We don’t want to try to outsmart this one. Photo from Tincan, 01.22.2023

In addition to the problematic buried surface hoar layer mentioned above, we are still concerned with the possibility of triggering a massive avalanche on weak snow buried 4-8′ deep around the Thanksgiving crust. As time goes on it is becoming less likely to trigger something like this, but with another loading event underway, we still need to treat the layer with caution. Deep slab problems are possibly the most frustrating and challenging to deal with, since they can remain reactive to human triggers for weeks without giving any warning signs before big avalanches release. We don’t expect to see any red flags (shooting cracks, collapsing) and it is really hard to test even in a more thorough test pit, because stability tests are less reliable once a layer is buried deeper than about 3′ or so. For now, it is still possible to trigger an avalanche on this weak layer from a thin spot in the snowpack, and if an avalanche does release it is likely to propagate very long distances around multiple terrain features and aspects. This weak layer is just too big and too dangerous to mess with. Given the reactive layer mentioned in problem 1 above, this is just one more reason to stay on low angle terrain.

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