Steamboat & Flat Tops
SnowpackAndrew McWilliams · Dec 11, 2024 · Steamboat & Flat Tops
Weather
Moderate westerly winds, temperatures in the teens, and partly cloudy skies.
Snowpack
Below about 9,000 feet, there was little snow on the ground. Shaded slopes had about 10cm to 30cm and sunny slopes were bare ground. From about 9,000 feet to 11,000, there was snow on sunny slopes, but it was patchy and its depth and continuity depended heavily on slope angle and tree cover (fewer trees or more slope angle equals less snow). Snow cover was continuous on shaded slopes and I found 20cm to 60cm of snow on the ground. This snow was generally faceted and weak and even sunny slopes had only thin and easily breakable crusts on the surface. In isolated areas, there were sun crusts strong enough to support me where there were no trees. There were generally two layers in this elevation band. Old October and November snow forming basal facets and depth hoar and the snow from the Thanksgiving Week storm and the most recent storm which is nearly completely faceted as well. I dug snow pits on an easterly slope near treeline (just above 11,000 feet). I found a similar structure to what we've been seeing across the Northern Mountains region. Snow from October and early November forms the basal facet layer. There is a denser layer of wind-packed snow (or crusts on sunny slopes) just below the Thanksgiving Week snow. This thin layer is quickly faceting, but the interface with this layer and the basal facets is my primary weak layer of concern. Above the Thanksgiving Week storm snow was a few centimeters of near-surface facets below the most recent storm snow - my secondary layer of concern. The wind stiffened the most recent snow into slabs a few centimeters thick. I saw cracking in this wind-stiffened layer and on steep rollovers I could easily push small slabs of snow breaking on the near-surface facets. These slabs were isolated to leeward terrain features and not continuous across the slope. I traveled across the top of a southeast-facing slope (the aspect most likely to be loaded from the recent wind) and this layer did not extend across the slope. The snow depth and structure were variable too. Some areas were composed completely of facets. Others had the new drifted snow above a crust above older snow. Generally, the snow depth on sunny slopes near treeline was about half what I saw on shaded slopes at the same elevation. I did not experience any shooting cracks or collapses on my tour, but I did avoid a steep northeast-facing slope on my descent. My snowpit tests had non-propagating results on the layers of concern, but my intuition told me that I should stick to the lower-angle slopes nearby. I didn't travel above treeline, but those slopes look heavily wind-affected with snow pressed into the slope. The light was challenging, but I likely some some old slides from around Thanksgiving on east-facing slopes. From what I could see, there was no activity on north or southeast-facing slopes - however this far from the event any old slide could just be melted out, blown out, or reloaded.