Vail & Summit County

Avalanche

Konigsberg, Zarter, Simenhois · Dec 21, 2023 · Vail & Summit County

Weather

Mild with a low cloud deck sometimes obscuring near treeline terrain. Winds were calm. It felt moist at lower elevations near I-70.

Snowpack

In our first, and lowest-elevation snowpit at 9400 feet on an east-facing slope, we got propagating results in an Extended Column Test (ECTP20) in the basal facet layer 15 cm from the ground. The snow height in this pit was 60 cm. Although we got propagating results, we all agreed this was a false unstable result due to the slab characteristics. The slab is composed of faceted crystals and mostly four-finger hard on the Hand Hardness Scale. We also got a non-propagating result on surface hoar buried 15 cm from the snow surface. In these shallow and weak areas, the surface hoar is interesting to look at, but most avalanches would step down to near the ground making the surface hoar more of a distraction than a problem. About 1500 feet higher, also on an east aspect, the snowpack was only about 75 cm deep. The slab was more cohesive than lower down but still composed of faceted crystals. A couple of thin crusts surrounded by faceted layers were buried in the snowpack. Normally a crust-facet combination would be alarming, but as noted with surface hoar from our first snowpit, the crust-facet combo isn't that important as the whole snowpack is weak and prone to avalanches near the ground with loading. As we rounded the corner to a more northerly-facing slope, also at 11,000 feet, the snowpack was deeper (110 cm) with an even more cohesive slab. We did not get any propagating results in ECTs. We performed a Propagation Saw Test (PST) on a surface hoar layer buried 20 cm from the surface with a result of PST 25/100 (SF). We also got a result of PST 35/100 (End) in the basal facets. It's possible that surface hoar can be an issue in these deeper snowpack areas as an avalanche can break on this layer with a smaller load. The line between a small load and smaller avalanches, and a larger load and bigger avalanches breaking on basal facets is unknown so it is best to travel in deeper areas thinking about the larger, more deeply-buried, and more dangerous persistent layer near the ground.---Surface conditions are very weak on northerly and east-facing slopes. On southeast-facing slopes the surface crust is about an inch thick.

Avalanche

None observed and with flat light it was hard to see activity from early December.