Vail & Summit County
AvalancheAndrew McWilliams · Dec 27, 2023 · Vail & Summit County
Weather
Single-digit temperatures warmed into the low teens with mostly sunny skies and light winds.
Snowpack
Snow depth in this near treeline area was about 80-100cm on northerly and easterly aspects with deeper drifts up to about 150cm. The general structure is similar to other areas in this large zone which includes the Gore Range, Front Range, Sawatch, and Elk Mountains. There is weak snow near the ground that shows propagating results in snowpit tests, but only after blows from the shoulder. There is a mid-pack slab that ranges in hardness from four-finger to pencil hard on the Hand Hardness Scale and there is a newly drifted slab above. The new slab is resting on weak snow above the mid-pack slab. Within the new slab, there are some grain size and density changes, but it is generally four-finger to fist hard. On more southerly aspects, there are crust layers near the ground, above the mid-pack slab, and within the newer slab. Where I was able to dig safely, there were only non-propagating results in Extended Column Tests associated with the new slab, but these results were after taps from the wrist. Some failures were within the new slab and others were at the new/old interface. In either case, these failures were on faceted grains that formed during the early December dry period. I did not hear any collapses in the snowpack as I traveled and got some minor cracking on steep, test slopes. On a steep east to southeast-facing bowl feature near treeline, a small cornice drop triggered a small slide within the new slab. This slide stepped down to the interface of the mid-pack slab and the new slab. This small avalanche then triggered a sympathetic slide at the new/old interface just to the south but within the same bowl feature. This second slide was larger and ran nearly to the valley bottom. When I investigated the crown, the new slab was more dense in this area than where I dug my snowpits - about one-finger hard.
Avalanche
A small piece of cornice triggered a small slide that stepped down to the interface of the newly drifted snow and the older slab. This slide caused a collapse and a crack ran across the top of the bowl feature. A sympathetic, larger avalanche ran just to the south of the first slide, but within the same bowl feature.