Southern San Juan
AvalancheChris Bilbrey · Dec 8, 2023 · Southern San Juan
Weather
Snowfall started around 10 AM and remained showery till late-afternoon. Periods of S2 snow followed by broken skies and pokes of sun delivered a couple inches of new snow. Moderate southwest wind along ridgetops contributed to light drifting onto leeward terrain.
Snowpack
Height of snow ranged 50 cm or less on southerly-facing slopes around 11,000 feet, and slightly higher. Those same aspects above the treeline were much thinner likely from wind-scouring and the recent warm-up aiding burnout. On west through north to east-facing slopes, height of snow ranged 60 to 80 cm. We found a robust, 1-inch thick crust on due south-facing slopes, but the same crust was thinner and more breakable on southeast and southwest-facing slopes. Regardless, near-surface facets linger below said crust, but we got the impression it needs a bigger new snow load to be a concern. Snow that fell today bonded well to the crust and did not sluff with ski pressure. Our snowpit on a west-facing slope near treeline yielded propagating failures in Extended Column Test (ECTP 22) and sudden planar failures in Compression Test (CT 15). Both tests failed in a 4F layer of 3 to 5 mm FC/ DH sandwiched between a pencil hard crust above, and a knife hard crust below. Our snowpit on a north-northwest-facing slope at treeline yielded propagating failures in ECTs (ECT 14) and sudden planar failures in CTs (CT 10). These test failed in the same weak layer as our west-facing snowpit, without the neighboring crust. The weak layer of concern on northerlies is thicker and more fragile - closer to 4F- hardness. An obvious near-surface facet layer lingers between the last two storm layers, is 1 to 2 mm in size, but did not produce failures in multiple tests. This layer provides a noticeable hardness change compared to the layer above and below, but by only one step.
Avalanche
Saw two old crowns from the last significant snowfall on November 30 to December 2. A little bit of fresh and drifted snow exist on the bed surface, but the crown and flanks still visible from the ridgeline above. Both slides traveled a good distance downhill (approx. 500 feet) given the shallow snow cover in the track. The avalanches failed in a 4F- layer of 3 to 5 mm FC/ DH at the ground.