Vail & Summit County
AvalancheAndrew McWilliams Ryan Zarter · Dec 6, 2024 · Vail & Summit County
Weather
Clear skies and light winds. Single-digit morning temperatures warmed to near freezing.
Snowpack
In snowpits near and below treeline on a north-facing slope, we observed large surface hoar grains on top of a degrading slab from November storms resting on facets above depth hoar. Below treeline, we only found non-propagating results in Extended Column Tests (ECTs), suggesting the slab isn't propagating failures. These occurred at the interface between an old wind-pack layer and a facet layer. There was a similar ECT result in our near treeline pit. We also found a propagating result near treeline between the facet layer described above and the depth hoar on the ground. Both pits were remarkably similar in structure, hardness, and depth. I can say anecdotally, that I think a slight difference in slab thickness and density likely made the difference. Like most of the Thanksgiving Week storm cycle avalanche activity, the weak layer of concern here is the facet layer resting on the depth hoar. Avalanches breaking at the top or bottom of that layer won't be significantly different from each other. Although we observed no signs of instability like cracking or collapsing, we did some old avalanches on the easterly-facing ridge of Bald Mountain. I dug on a west-facing slope near treeline as well. I found a snow height that varied quickly over a short distance from about 30cm to 80cm. There was discontinuous 5cm layer of dense, wind-packed snow on the surface. Where this was present I got easy propagating results in ECTs. Where the snowpack was thin on this slope there was no slab or structure to the snowpack at all. Where I dug on the thicker side of the slope, there was a similar layer of faceting storm snow, but the middle, wind-packed layer that we found across the north-facing slope was discontinuous. Where I found it, I could get non-propagating ECTs, where the old storm snow was resting on just basal facets, I got no results in ECTs - the snowpack was too soft. Overall, while places where you can trigger an avalanche are becoming more isolated and less reactive, you could still find a place to trigger an avalanche big enough to bury or kill you. Below treeline, the slab was faceted enough that LOW (Level 1 of 5) danger fits, but there was enough of a slab to be supportable to skis. If the snow continues to lose cohesion at lower elevations, we might start to see a Loose Dry avalanche problem develop.
Avalanche
These avalanches all likely ran during or shortly after the Thanksgiving Week storm.