Northern San Juan
AvalancheChris Bilbrey · Dec 11, 2023 · Northern San Juan
Weather
Abundant sunshine, light southwest wind, and temperatures in the mid 20s. Brief moments of harder wind gusts. Thin high clouds stayed to the north, but visible along ridgelines.
Snowpack
Average height of snow ranged 30 to 50 cm - drifts 60 to 70 cm deep. Steep, due south-facing slopes and terrain features that see brute force of winds were very thin or scoured to bare ground. Where snow depths were around 30 cm deep, the snowpack consisted of cohesionless, faceted snow (F to 4F) of varying grain size. Despite the weak top to bottom structure, the snowpack had just enough meat to keep us afloat. Where snow depths ranged 40 to 50 cm deep, we found an intact mid-pack slab (1F- to 1F). However, faceting is happening at the ground and on the surface in these spots. This setup was confined to elevation above 11,300 to 11,500 feet. Above treeline, the snow surface is a mix-bag of sastrugi, firm wind board, and shallower full-depth facet areas. Recent winds formed a 5 to 7 cm thick wind board on the surface that ranged P- to 1F hard, and small near-surface facets are developing below. The surface wind layer was breakable in spots, and we did not experience shooting cracks or collapses where we traveled. Probing across north and northwest-facing alpine slopes, old October snow and FC/ DH at the ground seemed variable in depth and distribution, and was generally 4F hard. Unable to determine the exact distribution of weaker snow below a cohesive slab, we avoided traveling on or directly below steeper terrain with a continuous slab connected across terrain features. Digging on an east-southeast-facing slope at 11,800 feet, we observed propagating results in Extended Column Test on 12 and 13 taps. Failures occurred in a 4F- layer of faceted snow grains (0.5 - 1.5 mm) below a thin, fragile crust. There is another easily identified NSF layer closer to the surface, but it did not produce propagating or non-propagating results.
Avalanche
None observed