Winds are strong and shifting direction as snow accumulates, creating a tricky pattern of wind slabs at upper elevations. Use caution around drifted slopes and convex roll-overs, especially where these slabs may overly a buried weak layer.
10-20 cm of new snow with strong winds changing in direction (from south to west to northwest) may form a complex pattern of reactive wind slabs on leeward terrain features at upper elevations. These areas of concern overlap with where cornices may also be reaching their breaking point.
A weak layer of near surface facets and surface hoar from February 22 may get buried down 40-70 cm. On solar aspects, these weak grains may be accompanied by a crust. As new snow and wind add to the slab above, there is concern for the size and consequences of avalanches on this persistent weak layer.
Friday night: Cloudy, 10-20 cm of snow, strong southwest winds, freezing level dropping to 500 m.
Saturday: Mostly cloudy, a trace of snow in the morning, northwest winds decreasing from moderate to light, freezing level 1000 m.
Sunday: Mostly clear, light variable winds, freezing level 1000 m.
Monday: Partly cloudy, isolated flurries with trace accumulations, light southwest winds, freezing level 1100 m.
By Friday afternoon, small (size 1-1.5) wind slabs were easily human-triggered on lee features in the alpine and upper treeline. These avalanches were breaking 20-30 cm deep.
On Wednesday, a large (size 2) human-triggered avalanche releasing on the February 22 surface hoar was reported.
Reports from earlier in the week include a natural storm and wind slab avalanche cycle up to size 2, primarily on northeast aspects in the alpine and upper treeline, releasing on the February 22 interface. This MIN post includes a photo of a skier triggered wind slab.
By Saturday afternoon, 10-20 cm of snow is forecast to accumulate as the freezing level drops below 500 m. Strong winds from the south are expected to switch to the northwest and decrease. This will likely create a complex pattern of reactive wind slabs on lee features at upper elevations and may bring cornices to their breaking point. Buried 40-70 cm deep, a weak layer of near surface facets or surface hoar from February 22 may persist and warrants careful evaluation.
Faceted snow and crusts exist near the base of the snowpack in much of the region. This layer is has been dormant recently.
