Northern San Juan

Avalanche

Colin Mitchell · Dec 18, 2020 · Northern San Juan

Weather

Clearing skies and warming temperatures today. Winds backed off with the departure of the storm and were calm at my profile site on the top of the pass. Radiation was strong and helped make it feel like a warm day.

Snowpack

Relatively simple structure in the study plot. The biggest changes from my 12.4 profile is that the snowpack has almost doubled in depth from 61 to 105, and, more significantly, a slab has formed over the late November/early December facet layer. ECT tests propagated with moderate taps on this layer, ECTP 17, ECTP 20. This structure has proven reactive to light loads with many natural and human-triggered avalanches occurring after relatively minor loading events. On Dec. 15th and today, we received 7" at our highway weather plot, and both times it was enough to initiate an avalanche cycle. The basal facet layer is solid at this elevation, and that does not appear to be changing. This layer got moist in November and re-froze in most areas, and has been the bed surface for the majority of our avalanches this season.

Avalanche

I saw several avalanches from Longfellow/Carbon Knob that came down near the county road. They are coded in separate observations.