Southern San Juan
AvalancheChris Bilbrey · Mar 28, 2023 · Southern San Juan
Weather
Following a frigid start, steady light to moderate southwest winds kept temperatures cool. Mostly sunny skies in the morning, then high clouds moved overhead in the afternoon. This helped the snow surface stay cool and dry on sunny slopes across elevation bands.
Snowpack
We found 6 to 8 inches of new snow that fell since the end of the last big storm cycle. The surface snow on northerly-facing slopes ranges F to 4F hardness, and sits above a generally 1F hard slab that formed during the 3/20-23 storm. Snowpits on a southeast and north-northwest aspect near treeline revealed between 70 and 90 cm of settled storm snow. Snowpack test produced overall stubborn result at a storm density change (CTRP 22/ Moderate force, shovel shear) around 50 cm deep, and at the new/ old snow faceted interface (CTRP 25). We also performed a deep tap test above a storm snow/ crust interface in our southeast-facing snowpit. This test produced DTSC 25 and failed below the crust in rounding facets/ re-frozen clustered grains. The reactive storm layer consisted of decomposing fragments and tiny faceted grains (0.3 to 0.5 mm), and was generally 4F hard. The buried faceted interface was about 4 to 5 cm thick (0.5 to 1 mm sized grains), and was generally 1F- hard. Cool temperatures recently has slowed down surface warming on sunny slopes, but a thin (2 to 3 cm) surface crust formed from the strong March sun. The crust was less robust on east and west-facing slopes below treeline, and less noticeable on the same aspects near and above treeline. Immediately below the crust is drier snow. We tried to initiate loose snow sluffs on steeper, easterly-facing test slopes in the afternoon without success. Seems like the snow surface needs the combination of abundant sunshine, less wind, and temperatures hovering around the freezing mark for loose wet activity to develop. Today's wind had more of a pressing affect to the snow surface versus slab forming. Isolated cracking made us think deeper drifts could remain slightly more reactive for a bit longer.
Avalanche
We triggered a couple of small, Loose Dry avalanches on northwest-facing slopes near treeline. These were confined to the most recent snowfall and occurred on slopes pushing slightly north of 35 degrees. None traveled far down the slope or entrained much additional snow volume.