Southern San Juan
AvalancheChris Bilbrey · Dec 13, 2020 · Southern San Juan
Weather
Beautiful sunny day with single digit temps to start and calm winds at pass level. Winds increased slightly during our morning tour, mostly observed near treeline and higher.
Snowpack
We found around 12 inches of new snow from our recent storm cycle above 11,000 feet. New snow was bonding well to a firm crust buried below on east through south-facing slopes below treeline. Exiting an east-facing below treeline slope around mid-day, the new snow did not sluff above the crust with ski pressure. As we climbed higher into the near treeline band, we began to observed loud, audible collapses and shooting cracks. These obvious clues of instability we're most evident in thick, wind-drifted areas and some cracking traveled outward in spiderweb fashion. Recent north winds thickened the upper storm slab, formed a soft/ breakable 2 inch thick wind-board on the surface and made the storm slab feel upside down. Wind exposed slopes near treeline and in the alpine had lots of wind-scouring, depositing, and many surfaces where we traveled were punchy to skis. North-facing slopes below treeline are definitely becoming a growing concern as depth of overlying slab above weak unconsolidated facets incrementally grows, but we were unable to get any snow to move on steeper slopes. The biggest concern on shady, below treeline slopes appears to be kicking off a loose snow avalanche that entrains the facet train while moving downhill.
Avalanche
We observed one soft slab slide that looks to be skier-triggered from the day before. Crown face located on the downside of a steep convexity. Slide failed at new/ old snow interface and did not step down to deeper layering.