With strong southwesterly winds overnight, which are forecasted to continue through today into tomorrow in the Alpine regions, and plenty of transportable snow, Wind Slabs will likely form on NW-N-NE-SE aspects near and above tree line, especially in favored locations (rocks, crossloaded gullies and chutes, leeward slopes, etc.) near tree line. Natural avalanches are possible, triggered releases are likely near tree line and above. There is the potential that a Wind Slab avalanche could trigger the deep weaknesses, discussed below, within the snowpack and the resulting avalanche could be large and destructive.
The latest discussion among local riders and snow nerds is the complexity of the snowpack, which isn’t typically for the Sierra, especially this late in the season. The snowpack complexity is a result of thin snow cover for a good portion of the winter, variable snow distribution, and cold temperatures, which allowed strong facet growth in the little snow cover available.
The wind slabs and storm slabs from last storm (3/1 – 3/3) have settled, but weak faceted layers that formed earlier in the season remain reactive deep in the snowpack. This is primarily confined to a narrow elevation band between ~9000’ to ~10500’, higher in some locations, and mostly on protected or sheltered NW-N-NE aspects where there has been enough snow all season to cover up bushes and other anchors that has the greatest potential for a large deep slab avalanches. With warmer temperatures, this deep weakness will gradually strengthen, but will likely remain a concern for at least the near future. In the upper elevations, deeper snow deposits and thick hard wind-slabs have helped to bridge over this weakness. In the Mammoth and June region the problem is most widespread due to greater snow coverage early season and more abundant protected and shelter slopes, less so in the Bishop and Virginia Lakes regions where snow lines were previously higher and sheltered snow coverage much more limited in distribution and depth.
* It’s that time of year where the snowpack is warming on most aspects but still cold on northerly shaded slopes, which can result in skins icing up in the soft snow after becoming saturated where the snow has become wet. Make sure to pack your skin wax or better yet pre-treat your skins before leaving for the field.
Caution – the lower elevation snow coverage remains thin with plenty of hazards lurking just below the snow surface (i.e. rocks, logs, and stumps). The snow is hiding plenty of hazards while providing little protection.