Southern San Juan
AvalancheAnonymous · Mar 27, 2020 · Southern San Juan
Weather
Intermittent snow squalls throughout the morning, showers became more intense and constant for most of the afternoon. For about an hour, around 4:00 pm, the clouds briefly broke and winds calmed before the next fairly intense wave of snow moved in and continued until at least 6:00 pm. Temperature dropped and winds picked up with each significant wave of snow if the afternoon. Winds were generally light below treeline, moderate near and above, and mostly SW. Snowfall rate reached S2 during the afternoon snowstorms but accumulation remained modest.
Snowpack
We found the same general snowpack structure that exists on many slopes in the La Plata mountains, a stiffening slab of varying size, comprised of our March snowfall events, overlying weaker, faceted grains. On southerly and some easterly slopes below treeline these facets simply make up the rest of the shallow snowpack to the ground; whereas on northeast, near treeline slopes, they are multiple layers of facets within the much deeper snowpack. New snow had accumulated to about 4” in sheltered areas near treeline and drifted up to 8” in spots below a ridge line, on a NE slope above treeline. It fell on top of a surface crust of varying thickness and strength on most aspects other than due north, shaded or protected features.
Avalanche
The new snow, with the help of consistent moderate winds was quick to become a very reactive small, soft slab; sliding easily on the old slippery snow surface, especially on steeper slopes. The terrain we were skiing (NE, near treeline) was generally less than 35 degrees with a few isolated terrain features that have increased steepness. We found one of these pockets on one of our runs, where it was steep enough for our slough to break into a larger slide. While the slide we triggered was certainly only D1 and confined to the very recent and modest snowfall, it did end up picking up a little bit more steam and running further out of the trees down the much lower angled apron than we expected. Also observed a natural avalanche than ran on the same newest snow/older surface interface on an above treeline, east facing, fairly cross-loaded gully, on the ridge between Gibbs and Burwell peaks (That is the slide shown in the picture).