Southern San Juan
AvalancheChris Bilbrey · Mar 11, 2021 · Southern San Juan
Weather
A mix of clouds, sun, and steady southwest winds. Blowing snow observed below treeline but winds did not have a stiffening affect to the snow surface until we climbed into near treeline elevations. We found 4 to 6 inches of new snow below treeline and up to 8 inches (20 cm's) at 11,600 feet.
Snowpack
Steady south-southwest winds are drifting and stiffening recent snowfall forming cohesive slabs near and above treeline. In more wind-protected areas, slab stiffening is less remarkable with generally good bonding between storm layers. A couple concerning layers of facets lurk in the upper snowpack. The upper most layer formed during a warm, dry spell about one week ago. This layer is slowly becoming more reactive as the overlying slab increases in depth and hardness. These near-surface facet grains appear more reactive in stability test and from ski pressure on slopes with a thin melt-freeze crust or wind-board above. On due north aspects, this same layer did not produce propagating results in test or give the same feedback on small test slopes. On those slopes, the new snow is accumulating directly above the facets. With additional snow and wind in the forecast, it will be important to evaluate sensitivity of buried weak snow before committing to bigger, steeper terrain. In addition, as surface slabs thicken in depth, the potential size of avalanches will increase too.
Avalanche
We observed several small, Wind-Slab avalanches near and above treeline that ran naturally in the last 24 to 36 hours. Also spotted a larger slide that we estimate ran in the last two days. It occurred on an east-facing slope in the alpine and looked similar to the slide observed near Snowdon Peak the day prior.