Southern San Juan
AvalancheChris Bilbrey · Dec 12, 2023 · Southern San Juan
Weather
Grey-bird, overcast day and mild temperatures. It felt humid for southwest Colorado. Southerly wind were light along ridgelines with an occasional moderate gust.
Snowpack
Average height of snow ranged 30 to 60 cm, but overall snow depths trended more toward the upper end of the range. Below about 10,500 feet, northerly-facing slopes revealed a somewhat promising snowpack structure despite snow depths hovering around 45 cm. These lower elevations lacked early-season snow, and where faceted snow sits at the ground, it was 10 cm thick or less. Compression Test produced resistant planar results with moderate-hard force. As we moved up in elevation, two common themes emerged - 1) depth of surface faceting increased and 2) weak snow at the ground got progressively deeper (around 15 cm). The most recent dry spell helped erode/ weaken the snowpack as a whole, but the middle portion (around 10 to 15 cm worth) is still 1F- hard. As we climbed above 11,000 feet, surface faceting increased to 20 cm deep, but remained 4F hard. East and southeast-facing slopes harbor a thin, breakable crust capping weaker near-surface facet (NSF) grains (4F-) than on northerly aspects. The crust was robust across slopes, but seems suspect to support a larger snow load. Recent north winds wrecked havoc on near and above treeline slopes, a made a lot of variability in snow depths across start zones and areas close to ridgelines. Deeper spots with a hard, wind board on the surface reside adjacent to spots where the snowpack is around 30 to 45 cm deep. In the shallower areas, the snowpack is fully faceted. Digging on several northeast-facing slopes near treeline, we found two weak layers of concern. One is a 4F NSF layer that formed between the last two storms and easily identifiable in our pits. This layer did not fail in test and this result is likely due to the degree of faceting above. The second layer is larger, 4F faceted grains at the ground. This layer produced resistant planar results with moderate force in Compression Test, and non-propagating results in Extended Column Test. The high degree of snow depth variability at upper elevations will likely play a big part in future stability, and not knowing where shallow trigger spots are.
Avalanche
None observed