Southern San Juan

Avalanche

Chris Bilbrey · Jan 27, 2020 · Southern San Juan

Weather

Light to moderate snowfall in the morning with moderate winds and stronger gusts. Around 1:30 pm, winds shifted from west-southwest to northwest, skies cleared, and snowfall ended. We found around 2 inches of new snow below 10,000 feet and upwards of 5 to 6 inches at higher elevations. Drifting around 8 to 10 inches deep below ridges and in cross-loaded terrain features.

Snowpack

We found shallow but touchy wind-slabs along exposed ridge lines and in cross-loaded terrain features. Overall they were small, but if winds continue overnight, they could grow to around a foot or more deep. The snowpack on slopes facing east to south remains the most concerning and the weakest - mostly at higher elevations but growing weaker below treeline. Westerly and northwest-facing slopes remain shallow but lack a cohesive slab above weaker snow on majority of slopes. Warm temperatures over the past couple days formed an ice hard melt-freeze crust on southerly-facing slopes with recent storm and wind-drifted snow stacked above. We observed a propagating failure with isolation in near-surface facets below this crust. Near-surface facets buried 12 to 16 inches deep that formed in early-January remain reactive in Extended Column Test failing with moderate force. On wind-sheltered near and below treeline slopes, recent storm snow showed good bonding on north and northeast-facing slopes from ski pressure and while jumping on small, steep test slopes. Signs of instability were limited to short cracks in thicker drifts and no collapses observed. In the big picture, the step-down factor on southeast and south-facing slopes remains possible with shallow slides triggering larger, more dangerous slides.

Avalanche

We triggered numerous but shallow Wind Slab avalanches failing at the new snow/ old snow interface above a firm melt-freeze crust. None ran far, mostly triggered right below ridge tops, and were confined to the new snow.