Southern San Juan
AvalancheChris Bilbrey · Dec 14, 2021 · Southern San Juan
Weather
Mixture of obscured and broken skies with periods of light snowfall that may have added up to around an inch by mid-afternoon. Winds were efficient at moving snow onto leeward terrain features above treeline. No effects to the snow surface near and below treeline from today's winds.
Snowpack
Last weeks storm snow is quickly settling into a cohesive 4F to 1F- slab. No instability observed on east to south-facing slopes where storm snow fell onto bare ground. A completely different scenario plays out on northerly-facing slopes where last weeks storm fell onto facets, depth hoar and faceted crust. The snowpack below treeline remains thin, around 70 cm's deep, and holdover snow from the fall is more isolated below the upper slab. As you climb higher in elevation, holdover snow is deeper and found more consistently across slopes. We observed lots of cracking and collapsing with some cracks shooting outward around 100 feet. Despite the upper slab being more supportable to skis, we easily punched through to the ground once stepping off our skis. Elevated winds during the afternoon contributed to blowing and drifting snow mostly above treeline.
Avalanche
Widespread natural activity from last weeks storm on northerly-facing terrain near treeline. It appears that one or more slides originating from above treeline ran down into near treeline and sympathetically triggered many smaller slides. Some of the slides produced avalanche flow on slopes around 32 degrees and ran up to 300 feet down treed slopes. These slides seem to have run during the middle of our last storm cycle, and around a foot of new snow exist on the bed surface. These slides failed on faceted grains in the lower snowpack.