Vail & Summit County
AvalancheAndrew McWilliams · Dec 21, 2023 · Vail & Summit County
Weather
Broken skies and temperatures near freezing. Moderate winds out of the northwest at ridgetop.
Snowpack
We observed a thin, weak snowpack less than a meter deep everywhere we traveled. There was some localized collapsing on east aspects below treeline, but nothing similar to the rumbling collapses we saw last week. While there is a midpack slab near and below treeline, at lower elevations and in protected areas, the slab was only four-finger hard on the Hand Hardness Scale. At higher elevations and areas with more exposure to wind this slab ranged from pencil to one-finger hard. Where we dug on the margin of a southeast-facing slope near treeline, the slab was between one-finger and four-finger hard and the height of snow ranged from about 40cm to 80cm. There were multiple crust facet combinations with thin weak crusts sandwiching fist-hard layers of faceted snow above the slab. Below the slab was a thin layer of depth hoar. The primary layer of concern is still the depth hoar interface with the slab and we saw propagating results after one tap from the elbow in an Extended Column Test. The snow above the slab is too weak to propagate a failure. We saw ski tracks on that slope and had no signs of instability like cracking or collapsing. It seems possible that our test results suggest the snowpack is more unstable than it actually is. Our pit location was in a thin area on the margin of the slope and while it was representative of the structure, it could have made it easier to affect the weak layer in snowpit tests. Regardless, while it has become harder to trigger an avalanche this weak, the current structure reads like a recipe for avalanches if we get additional snow, especially if it comes with strong westerly winds. It won't take much weight to reactivate the weak layer near the ground and the weak snow near the surface could become a new layer of concern.
Avalanche
An old avalanche on a southeast near treeline slope near Sts. John. This avalanche likely ran in early December, the last time there was significant snowfall.