Northern San Juan

Avalanche

Chris Dickson · Dec 10, 2021 · Northern San Juan

Weather

15" of new snow at the trailhead, with storm totals increasing as we ascended (max est. HN24: 25"). There was light snowfall throughout our tour, with winds picking up and temperatures dropping while we were out there. WSW winds have built sensitive cornices on the east side of a ridge and drifting/wind compaction was observed NTL. At 11,000', 70cms (27") of new snow (from Monday until now) was measured, sitting on top of 5cms of meltforms on a slightly SE aspect.

Snowpack

We observed many red flag indicators of unstable snow: extensive cracking adjacent to the skintrack, a large collapse in an east-facing clearing, persistent slab avalanches remotely triggered on N-facing aspects as far as 50ft from the skintrack, and small natural D1 persistent slab avalanches on numerous NE aspects. Basically, wherever there was old faceted snow under the new snow, we saw reactivity on that old/new snow interface. On E and SE aspects, spot probing revealed that the new snow was sitting on previously bare ground and was far less reactive. The smallest change in aspect created drastic differences in reactivity. The most dangerous slopes were any that harbored old faceted snow, and the safest slopes were bare ground prior to this storm.

Avalanche

Avalanches observed include: 1. SS-N-R1-D1 at 10,800' (BTL) on a NE aspect 2. SS-ASr-R2-D2 at 11,280' (BTL) on N aspect 3. SS-ASu-R2-D2 at 11,200' (BTL) on a NE aspect 4. SS-ASu-R2-D2 at 11,400' (NTL) on a E aspect (wind loaded pocket below the ridgetop) I did not set off these slides, but am reporting them with permission from the parties that did. Stepping out of the skintrack, I did trigger a large collapse that created cracking in the new snow on an E aspect. The storm slab slid a few inches downhill then arrested (slope angle was 30*).