Northern San Juan
AvalancheAmy Pertuz · Dec 28, 2022 · Northern San Juan
Weather
A mid afternoon lull in precipitation was followed by a snowy and blustery finish to the day, with precipitation S2-S4 in the end of the afternoon, and moderate blowing snow. Winds shifted towards west in the afternoon after being southwest most of the day.
Snowpack
The west and northwest-facing slopes were much more reactive than easterlies today. HN24 10" by end of the day, with drifts to 15" in areas travelled. Cracking was common on west and northwest aspects near and below treeline, but large-scale collapsing a little less so. It seems from the reactivity that the weak surface facets and possibly surface hoar were better preserved prior to the storm over in this area (Putney zone) though I could not find preserved buried surface hoar. A pit on a west aspect near treeline showed a concerning structure, with 8 taps required for propagating ECT results (ECTP) on a facet layer which sits just below a prominent mid-pack wind crust 50cm below the surface. The west aspects are mostly faceted, but this wind-stiffened layer provides just enough cohesion to allow the softer surface snows above it to still act as a slab. I would expect this aspect to become more reactive with ongoing storm snows and slab stiffening. On a NW aspect NTL, the HS was 85 cm, and largely faceted. Stiffer layers in the upper mid pack provide just enough supportability to travel on, but trap-door conditions can be found on northwest aspect below tree line where most of the snowpack is faceted and weak.
Avalanche
In a brief window of visibility in the afternoon, spotted two slides which appeared to have run early in the storm, and were likely the result of wind-drifting from SW winds. Both Trico Ridge area, ATL NE, appeared to involve storm snow only