Southern San Juan
AvalancheChris Bilbrey · Jan 22, 2021 · Southern San Juan
Weather
Skies were mostly overcast with intermittent periods of obscured peaks. Light snow showers gave way to steady snowfall by 3 pm with light to moderate winds at treeline and higher. About 2 inches of new snow accumulated in the last 24 hours.
Snowpack
The snowpack on north and northwest-facing slopes near and below treeline is soft, unconsolidated, and includes several layers of weak faceted snow - topped off with a couple inches of goose down feather snow. Despite an overall weak structure, the missing ingredient is a cohesive slab. Compression test identified weak interfaces but Extended Column Test failed to produce propagating results. This may all change rather quick if the upcoming storm adds a large load. As we approached treeline and alpine slopes, the upper snowpack became more supportable and evidence of recent strong winds was obvious. Poking our poles in the snow helped identify areas with harder layers capping softer layers. The most concerning wind-drifted layer was about a foot below the surface with near-surface facets below. The overlying, soft slab was not enough of a load to contribute to propagating results in stability test or other signs of unstable snow. In our alpine snowpit, the 12/11 interface sat below about 70 cm's of snow, was starting to round, and unreactive in test with a thick, stiff (1F) slab above. The tricky part is the alpine boads the most variability in terms of snow depth and coverage. Knowing exactly where the concerning slab, weak layer combinations exist is difficult now that evidence of prior drifting is hidden by recent snowfall.
Avalanche
No recent slides observed. We did see 1 (assuming natural) older avalanche that probably ran sometime in early January during one of the strong wind events. The slide occurred on a northeast aspect in the alpine and looked to be confined to upper snow layers.