Cayoosh- Armchair and Lazyboy
5 days were spent in the Cayoosh Basin of Armchair and Lazyboy. ACMG guides present were Leslie Manley, Daniel Robb, and Sam McKoy.
Intense winds with minimal precip on the 14th redistributed snow extensively at alpine and treeline through the day and night. Natural avalanches could be heard and the next morning (15th) temperatures had cooled and the freezing level dropped. With this colder temp following warm storms the surface snow tightened. On the 15th we observed the remnants of a large natural cycle due to the wind loading. These wind-slabs ranged from size 1-3.5 and likely ran on the Dec 8th interface or within the storm snow. See photos.
On the 15th, numerous pits were dug and the Dec 8th interface was most prominent at treeline up to 2000m. Above 2000m, snow levels increased from 150cm to 200-300cm. Above this elevation and in wind exposed areas, the Nov crust was the most prominent weak layer. Due to the variability of the winds, shallower areas (~100cm) were reactive to compression test results (moderate sudden collapse). Propagation saw tests on this layer produced 60/100 END results on this layer. Wumphing was heard above 2000m in sheltered areas, which indicates potential surface hoar at the Dec 8th interface where the wind did not destroy these crystals.
At treeline and below, the December 8th surface hoar was highly reactive and ranged from 10-20mm, standing. These sat on top of a facetted crust and was highly reactive in lower elevations. At treeline elevations, this layer produced easy to moderate sudden collapse results and repeatable easy/moderate ECTP results. At this treeline elevation, a member of the public likely triggered a size 2 windslab that failed on this layer (see photos 1, 2 & 3 of 3). This avalanche covered some of the up-track.
The following days after this break on the 15th brought more precipitation, accompanied by moderate to extreme winds and added another 55+ cm to HST in area. Storm slab avalanches up to size 2 continued at treeline and size 3 in Alp.
By Dec 18th, the Dec 8th surface hoar and facets are down 120 and snow depth of approximately 205 at treeline
Overall, a lot of now and extensive change in the mountains over 5 days. We skied conservative terrain and observed as these changes were happening. These layers likely continue to get buried deeper.