Southern San Juan

Avalanche

Chris Bilbrey · Mar 15, 2021 · Southern San Juan

Weather

Sunny day with scattered clouds passing overhead. Light winds through mid-afternoon kept temperature cool, but winds became calm by 3 pm and felt like temperatures bumped upward a few degrees. Winds transitioned from northwest to west signaling the beginnings of our next storm system.

Snowpack

It is starting to feel more like spring in Southwest Colorado with the snowpack going through rapid changes each day, especially after new snow and sunny skies. We observed 4 to 6 inches of settlement in the new snow and southerly-facing slopes got heavy and moist by the afternoon forming a thin crust once the sun descended behind the ridge. Northerly-facing slopes at all elevations remained dry and soft but not the "cold smoke" snow as the day prior. Recent winds made the surface snow feel slabby once we climbed above 11,000 feet but no surface cracking noted. Near treeline slopes harbor a stiffer, 1F surface layer with F+ snow below. This harder layer was around 4 to 5 inches thick and didn't contribute to a change in stability test results where we dug. A concerning crust/ facet combo observed down 45 cm's from the surface on northeast and east-facing slopes that is most likely the same layer associated with recent natural activity. This layer failed with moderate force in Compression Test (SC failures) and Extended Column Test produced non-propagating results with 24 taps on the same layer. Another 4F facet layer observed around 60 cm's down and only produced dirty failures. Seems like the recent storm snow was not enough water weight to drive instability outside of wind-drifted areas. With more snow on the way, evaluating these weak layers in the upper snowpack is prudent before committing to steeper terrain.

Avalanche

We observed several crown lines below ridgelines on northeast, east, and southeast that most likely ran on 3/14. However, continued snowfall and drifting after they ran filled in most of the evidence making it difficult to accurately code individual slides. There was also evidence of numerous long-running Loose Dry avalanches that ran on 3/14 during the storm. Today's strong sun kicked off numerous but small Loose Wet avalanches mostly on south aspects in the alpine. They traveled far but didn't appear to entrain a lot of additional snow.