Steamboat & Flat Tops
AvalancheDylan Craaybeek, Andrew McWilliams · Jan 4, 2023 · Steamboat & Flat Tops
Weather
Temperatures fluctuating between 15-30F throughout the day with mostly Broken sky cover and intermittent snowfall never more than S2. Light wind with Moderate northwest gusts on top of the Flat Tops and Moderate snow transport all day.
Snowpack
Deep snowpack with the height of snow (HS) averaging between 160-190cm on northerly and easterly aspects and around 120-150cm on westerly and southerly aspects. Wind-loaded slopes were well over 2m deep. There were a number of potential weak layers in the new snow including two distinct melt-freeze crusts (MFcr), and a very thin layer of near-surface facets (FCsf) in the top meter of the snowpack. Small column snowpack tests showed unstable results with sudden collapse and sudden planar results on compression tests and numerous planar failures on shear tests but none of these layers showed any propagation potential on long-column tests including extended column tests and propagations saw tests. All slopes dug to to the base on still have very well-developed facets and depth hoar at the bottom 20-40cm of the snowpack. While no extended column tests failed on this layer propagation saw tests showed unstable results (PST END 39/120 and 34/150). All of this data indicates that there may be some new snow instabilities for the next few days to week in this area but for the most part the flattops moved into the low-probability, high-consequence deeply buried Persistent Slab avalanche problem with the basal facets being the layer of concern. Further evidence of this is discussing conditions with another group of snowmobilers they explained how they experience a "very scary and large collapse when three of us were stopped on a slope and a fourth snowmobiler came up and stopped next to us." It would seem the weight of four snowmobiles and their riders is enough to cause a failure in the weak layer buried around 150cm deep on most slopes.
Avalanche
Some cornice falls and loose dry avalanches were observed on steep slopes. Low visibility likely prevented us from seeing any other larger avalanches nearby. Evidence of previous avalanche activity may also have been obscured by additional snow and wind drifting.