Virginia Lakes

A persistent problem exists in some regions of the forecast area where weak, old, faceted snow buried on 11/23 lingers at the base of the snowpack. While it is possible to trigger an avalanche on this reactive layer, the problem appears isolated to pieces of northerly terrain. 

Collapsed a single ~25' radius when stepping out of skis to start digging on a N/NE slope at ~10200'. Whumpf was very audible; however, no cracking was observed. This occurrence was backed up by the results and structure in the adjacent snowpit (see snowpack observations below).

Near the trailhead, we found 10-20cm of snow on the ground. Cimbing the benches above Red Lake (9700'-9900'), we found an HS of 55cm on windward terrain and 100cm on the leeward sides. As we climbed higher, we found multiple 5-55cm wind slabs to be stubborn to unreactive (see photo). S-SE aspects were moistening throughout the day, with the base of the snowpack on these slopes also moist by mid-afternoon.

As we approached ~10,200', we felt weakness at the bottom of the snowpack in spatially variable locations while probing with the backs of our ski poles. We decided to dig in one location where we felt the weakness—a N/NE facing slope—and in another location 70' away on a due E slope where the weakness was not present. In the E-facing pit, we found weak faceted snow (FC) at the base of the 60cm snowpack, but we did not get any propagating results (ECTN22). Meanwhile, I collapsed a 25' radius around me while stepping out of my skis into the snowpack with a very audible whumpf. I also found weak facets (FC) at the bottom 5-7cm of the 71cm snowpack, however both my small and large column tests failed on isolation (ECTPV and CTV). These very different results just 70' apart paint the spatial variability of this isolated, reactive, persistent issue. 

While facets were present at the base of the snowpack throughout near-treeline terrain on E-N-NW aspects, the presence of an overlying slab to trigger on top of these weak grains was isolated to areas downwind of tree fences and mid-slope rollovers. This is where the soft slab rests over the weak layer and where smooth ground cover means that the facets arean't broken up by sage or rocks. In shallower areas, like our E-facing pit location, there is no slab present to trigger on top of the weak grains.