Northern San Juan
AvalancheColin Mitchell · Feb 26, 2020 · Northern San Juan
Weather
Cold and clear morning. Single digits at the trailhead, but temperatures warmed into the teens by midday. Moderate northwest winds slowed through the day. Some clouds rolled in late morning, and skies were scattered to broken in the afternoon.
Snowpack
Around 10" of storm snow fell in this area. Strong northwest winds during and after the storm stripped most northerly through westerly slopes, ridges, and mid-slope terrain features. More protected areas varied between 10-20" of 4F-hard wind-packed snow, and smooth, K-hard wind slabs. All this was topping old crust and facet layers on southerly-facing slopes and a deep, well-consolidated snowpack on northerlies. Southerly-facing slopes were clearly loaded from recent winds, and the drifting and slabs extended well down below ridgelines. We experienced several small to medium-sized collapses on these slopes during our ascent. While climbing the ridge between the Minnehaha and Bonita Peak drainages, I remote triggered a cornice drop, which triggered an avalanche on a south-southeast aspect. The slope was heavily wind-loaded. A natural avalanche had run in the past 48 hours just a few hundred feet away from today's slide. The snowpack at the trigger point, was several layers of very hard wind slabs and buried facets.
Avalanche
We spotted two avalanches which had run during recent storms or the wind event that followed, and remote-triggered one while climbing. All were on S-SE aspects just above treeline.