Vail & Summit County
SnowpackAndrew McWilliams · Nov 19, 2024 · Vail & Summit County
Weather
Snow fell all day averaging S1. Winds picked up in the afternoon from the northwest with temperatures in the single digits. There was about 2" of snow on my car when I returned.
Snowpack
Below 10,000 there was a single, thin layer of snow on the ground. Between about 10,000 and 11,000 feet, there were two layers in most places - accumulating storm snow and old snow. On sunny slopes, the old snow had a crust on top. There was about 30cm to 45cm of snow on the ground. Above 11,000 feet there were three layers in the snowpack on shaded slopes and one or two crust layers with old snow in-between on sunny slopes; the depth increased to 45cm to 60cm. Once I got to the upper end of the near treeline elevation band, I found drifted areas close to a meter, but there were still a lot of shallow areas. Below and at the lower end of near treeline there was no slab in the old or the new snow. Once I broke treeline, you could feel an old, dense slab from the strong southwest winds last week and in some drifted areas the storm snow was four-finger hard on the Hand Hardness Scale. I got some cracking on the low-angle north-facing slope where I dug a pit at about 11,800 feet. With poor visibility, I avoided steep slopes entirely, but I think you could have made a small avalanche on a steep, drifted slope. There was about 15cm to 25cm of storm snow that fell overnight and throughout the day resting on near-surface facets above the older wind-packed layer. Chunks of the storm snow easily fell off the skin track on my ascent and there were non-propagating fractures at that interface underneath my shovel in Extended Column Tests (ECTs). I got one propagating result in an ECT just below the older wind-packed layer in another layer of near-surface facets. These were likely buried around November 12. I attempted to repeat this result but was unable to in a subsequent test - that test had no results. In a snowpit on a similar aspect just below the treeline, I found a similar structure, but there was no slab and my ECTs had no result. I didn't see any failures at the basal facet interface in either snowpit, but I think the snow was too soft where I dug. If you found a slope where the November snow was a little harder and the facets a little weaker and thicker, I think you would see a result in a snowpit test. We'll see how this layer reacts to the new load and if there is another round of avalanches that break near the ground. Southerly-facing slopes had about two-thirds to half the snow of northerly-facing slopes. Most of these slopes lack sufficient snow for avalanches at the moment, but this new snow could change that. Moving forward, if weak snow develops on the surface and gets buried we could see the possible size and distribution of new snow avalanches increase; there is enough coverage now in north, northeast, and east-facing start zones near and above treeline. With a big enough storm, we could see our first CONSIDERABLE (Level 3 of 5) danger of the season due to easily triggered small to large new snow avalanches and/or an increase in sensitivity of our Persistent Slab avalanche problem. We'll need to investigate the recently buried near-surface facet layers to determine how widespread their distribution is and if there is a new Persistent Slab concern.