Southern San Juan
AvalancheChris Bilbrey · Mar 11, 2023 · Southern San Juan
Weather
A pacific northwest kind of day. Mild and damp with off and on snowfall above 9,000 feet, and shraining (looks like snow but feels like rain) below that to the valley bottom. Clouds broke around 11 am providing good views into alpine terrain. Heavy snowfall picked back up around 3 pm. Moderate winds with occasional strong gust along a treed ridgeline around 11,000 feet.
Snowpack
We found 20 to 30 cm of new snow from the valley bottom to around 9,500 feet. New snow depths ranged 45 to 60 cm from about 10,000 feet to above 11,000 feet. The new snow was very dense with a Styrofoam surface. Ski penetration was mostly 6 to 8 inches and slightly deeper on shady slopes. We easily punched through into weaker, facets below the storm snow on shady slopes once out of our skis. The storm snow felt more inverted on north through east-facing slopes, but we found the same softer layer midway down in the storm snow across all aspects. This storm layer/ density change consistently produced progressive and sudden collapse failures in CTs with around 10 taps, but no results observed in ECTs. A snowpit on an east-northeast aspect revealed a 20 cm layer of 4F faceted grains below the new snow. The overlying slab was 1F- to 1F (top to bottom), 60 cm deep, and multiple ECTs produced propagating failures with 11 taps. Slopes facing southeast through south to west had a firm crust below the new snow, with softer clustered rounds beneath. We observed fairly good bonding to the crust and mostly resistant planar failures with moderate force in CTs. These results suggest that you may be able to initiate a slide on steeper slopes where the new snow rest above a crust. No cracking or audible collapses throughout our travels. This storm arrived with plenty of warm, moist air and it appears liquid precipitation fell at various times below 9,000 feet. This contributed to many small loose wet slides originating on slopes around 35 degrees and from the base of cliffs or near exposed rocks. Very brief moments of sunshine today help the snow on sunny slopes set up quick and those same slopes developed a micro-thin crust once cloud cover returned.
Avalanche
Several size 2-2.5 natural avalanches in the Madden Creek drainage. All slides appeared to fail at the new/ old interface. None of them appeared to step down into deeper PWLs. A few of the slides propagated wide across the terrain.