Southern San Juan
SnowpackChris Bilbrey · Feb 16, 2021 · Southern San Juan
Weather
Today's weather was a mix of broken skies and periods of sunshine followed by S2 snow showers. Wash and repeat. Snowfall today didn't amount to measurable accumulations. Moderate west-northwest winds along ridge tops built fresh drifts 18 to 24 inches thick.
Snowpack
New snow depths ranged from 4 inches along the valley bottom to around 8 inches at 10,000 feet and over a foot above 11,000 feet. Moderate west-northwest wind drifted recent storm snow into 18 to 24 inch drifts along ridge tops. As we climbed to about 11,200 feet, newly formed slabs remained soft and only minor cracking noted below skis. However, and while approaching a heavily wind-loaded southeast-facing slope, we remote triggered a large avalanche that failed above a melt-freeze crust. The firm bed surface formed during a 3-day warm, dry spell prior to the start of snowfall on February 10th. A snowpit on a north aspect and slightly higher in elevation to the triggered slide showed decent bonding between recent storm layers and the 1/19 near-surface facet layer. We observed non-propagating results in Extended Column Test in individual layers in the top meter of the snowpack, and Compression Test produced sudden planar failures at the 1/19 interface with moderate force. Snowfall since February 10th is close to 3 feet deep and triggering even a small slide in steeper terrain could be dangerous considering recent snow volume only.