Southern San Juan
AvalancheChris Bilbrey · Feb 18, 2023 · Southern San Juan
Weather
High thin clouds kept temperatures on the cool side. A moderate southwest wind was drifting the recent storm snow back onto easterly-facing slopes. The wind was steady enough to start eroding a surface crust that formed the day prior on the west and southwest aspects from sunny skies and warm temperatures.
Snowpack
Lots of visible settlement in the latest storm snow - around 8 to 10 inches. Since our travels four days ago, trail breaking has gone from just over boot top to between 10 and 20 cm today depending on the aspect. Slopes that see direct sunshine below the treeline had a firm surface crust generally an inch thick. Similar surface conditions were found on the same aspects near the treeline but the crust was about half the thickness, with softer snow (decomposing fragments) below. The extent and thickness of the crust became less robust the higher we climbed in elevation. Shady slopes at all elevations still hold soft, cold snow on the surface and east and west-facing slopes above the treeline were softer versus crustier. Snowpits below and near the treeline on east-northeast aspects yielded a mostly 1F storm slab (65 cm and 88 cm respectively) above the Valentine's Day interface, and this persistent weak layer has transitioned into a 1F- hard layer of rounding facets. We observed dirty failures in CTs in upper storm layer density/ hardness changes and no results at the 2/14 interface in our below treeline pit. When prying the isolated column after completing the CTs, the block split at the 2/14 interface. There appears to be a lot of friction between the rounding facets and the dense storm layer above preventing failures in tests. In our near treeline snowpit, we found a thicker settled storm slab above the 2/14 interface with a similar grain form and size. This interface produced mixed results in CTs and an ECTX. These results suggest that finding an area of the slope where the slab is a bit shallower may be where a rider or machine could provoke a failure at the 2/14 interface. Additionally, areas that slid during the last storm cycle now have a much shallower, softer slab above the 2/14 interface. The PWLs there are weaker and more angular than where buried deeper but lack enough snow volume above at present to fail with ski pressure. Those places seem more likely to run again with additional snowfall next week.
Avalanche
We spotted numerous slides that likely ran during the latest storm cycle on February 15, 2023. Inspecting a few crown lines on our travels suggest these slides failed at the new/ old snow interface buried on Valentine's Day.