Southern San Juan
AvalancheAnonymous · Jan 2, 2021 · Southern San Juan
Weather
Mildly cool ambient temps, mostly clear skies. Winds remained light with moderate gusts in many areas we traveled near and below treeline but looked to be strong in the alpine, picking up plenty of snow.
Snowpack
On E-NE-N aspect below and near treeline we found varying snow depths with an unconsolidated snowpack in shallow areas. We experienced a couple of small, localized whumphs on more easterly and wind loaded slopes. The snowpack on these aspects consisted of a F-4F slab of the new storm snow since mid-December with a very thin layer of facets in the middle; capping plenty of larger grain facets below, though they appear to be slowing gaining strength. Stability tests on more due northerly, protected slopes near treeline still produced failures with moderate force on the interface between the layers of new storm snow but was much more stubborn to initiate failures lower down in the snowpack, and the fractures there were very non-planar. None of our tests produced propagating results.
Avalanche
We observed a large natural avalanche on an east aspect at about 11,400 feet near Star peak. The avalanche broke just about at treeline, and the crown spanned almost the entire width of the path and ran through sparse trees to the deeper gully below. The path is very susceptible to cross-loading from southwest then northwest winds. It appeared to have only broken on the interface between our recent storm snow but still propagated wide and ran far into a nasty terrain trap.