Vail & Summit County
AvalancheJason Konigsberg · Feb 6, 2018 · Vail & Summit County
Weather
Skies changed from scattered to obscured and snowing lightly in the late morning. Winds were generally light and no blowing snow was observed. On the drive home it seemed that the winds had increases as there was blowing snow across sections of highway.
Snowpack
No cracking or collapsing was observed and the new snow seemed to be bonded well to underlying snow surfaces. There wasn't much previous wind loading and the new snow seemed fairly evenly distributed.---Below treeline (below about 11k ft) the snowpack is mostly faceted with about a foot of right-side-up snow on top. HS (height of snow) is about 90 cms.---The snowpack is much deeper with many different layers at the near-treeline elevation band. HS is about 150 to 160 cms. The weakest layer, on northerly slopes, continues to be the top of the depth hoar layer that sits about 50 cms from the ground. I did not get any propagation in an ECT. When I removed some of the slab in a modified ECT test, the layer propagated a fracture. In these areas with a 4 to 5 foot snowpack, Persistent Slab avalanches will become hard to trigger. Conditions are much thinner and very different in the western part of the zone.---On southerly slopes the basal weak layers consist mostly of 1-2 mm facets, but there is well-developed depth hoar near the ground. Southerly, near-treeline slopes HS = ~115cms. There is a two inch thick melt-freeze crust below the last week's storm snow that is capable of supporting a load and preventing collapse of any deeper weak layers.
Avalanche
With decent visibility at times only one avalanche observed in the surrounding mountains. This avalanche may have been triggered by cornice fall.