Northern San Juan

I travelled around the US Basin avalanches that were triggered remotely on Saturday, 2/21. The crown lines of the two largest avalanches were over a meter deep associated with heavy drifting onto north and northeast slopes by strong southwest winds. Below the drifted areas the flanks of the avalanche were much shallower. The bed surface suggested that the avalanches broke in very shallow, weak, and rocky areas just below steep convexities and gouged to the ground in places. The pit I dug on a northeast slope was near an old avalanche and likely consistent with the snowpack structure of the avalanched slopes.

Warm and muggy. A weak overnight freeze and overcast skies made today feel like a day of change for our mountains.

Around 40 cm of settled storm snow sits above a weak snowpack on sheltered slopes that tilt to the north. While southeast to south through west slopes have been cooked by recent sun and warm temperatures below 12,000 feet, slopes that tilt to the north maintain dry snow and a winter snowpack. These slopes that tilt north remain the most concerning slopes moving forward. The firm-over-weak structure will persist for some time, while audible and visual signs of instability will wane. Below treeline I received no propagating results on a north slope. Notably, this was an area where I had full snowpack boot penetration. In these areas, it seems as though the snowpack lacks the 1-Finger mid-pack slab that many of the propagating results have been failing below. I suspect areas below treeline that carry a firmer mid-pack slab to be more prone to avalanches (and propagating test results). These areas are likely trigger points like convex rolls on steep open slopes. Near treeline I was able to find a 1 Finger mid-pack slab on many open slopes. This mid-pack slab corresponded to a layer about 30cm down that was supportable to boot penetration. I received moderate propagating failures on northwest and northeast slopes below this 1-Finger layer.