Carefully assess for the presence of a persistent weak layer before committing to a slope. If in doubt choose simple terrain.
30-50 cm of recent snow has been redistributed into wind slabs at upper elevations. variable winds over the past few days mean that wind slab could be found on all aspects. Previous strong south winds have formed large over hanging cornices that pose a significant hazard as well.
30-70 of recent snow sits over a facet-crust weak layer combination that is possible to human trigger. Recent observations demonstrate the potential for this problem to be triggered remotely and release sympathetic avalanches in adjacent terrain.
Wednesday night: light snow and moderate west winds. Low of -8 at 1400m.
Thursday: light flurries and light to moderate west winds. Freezing level rising to 1000m.
Friday: stormy with 10cm of new snow.Strong southwest winds with extreme gusts. Freezing level rising to 1400m.
Saturday: light flurries with moderate northwest winds. Freezing level rising to 1400m.
On Tuesday, we received report of a large (size 2.5) human-triggered avalanche near Rainbow Mountain that caught and carried a group of five skiers. The avalanche released on north aspect at 1900 m. It broke 40 cm deep and ran on the late January facet-crust layer. The avalanche propagated across adjacent roll-over features and triggered a sympathetic slide on a small feature 200 m away.
A skier remote size 2 was also observed on a northeast aspect at 1900m on Tuesday. This avalanche released on the same layer from late January.
On Monday, operators reported numerous large (size 2-2.5) human and explosive-triggered avalanches breaking 20-50 cm deep in the recent storm snow. In a few areas, these slabs broke 70-100 cm deep. In the backcountry, a group remotely triggered an avalanche from Panorama Ridge on a northeast aspect in the alpine. Near Gin Peak, a skier was caught and carried in a small avalanche that released on a steep, convex feature at treeline. On Sunday, a group also travelling near Gin Peak reported triggering a small (size 1.5) avalanche. The avalanche was triggered remotely from below and broke 50 cm deep.
Last week, explosive control work near Whistler produced a cornice fall that triggered a size 2.5 deep persistent slab on the weak faceted crystals above the early December crust. The slab broke 60-130cm deep. This indicates that while the weak layer is unlikely to be affected by skiers and riders, it could still be triggered by very large loads.
Winds have varied in direction over the past few days redistributing up to 50cm of recent storm snow into wind slabs on all aspects. The recent snow rests on a problematic layer combination. Weak sugary facets formed during a prolonged dry period over a thick melt-freeze crust. In sheltered areas at upper elevations, surface hoar may also be found on the crust. This late January facet-crust layer has demonstrated continuing reactivity in the aftermath of the weekend storm. Travelers have reported remote-triggered avalanche activity, widespread whumpfing on this layer (see this report from Paul Ridge), and reactivity in snowpack tests (see this report from Gin Peak).
Deeper in the snowpack, it is possible to find another crust layer buried down 100-200 cm with facets above it from December. This layer is most prominent between 1700-2100 m and is currently classified as dormant; although large loads such as a cornice failure or avalanches in motion may still be able to trigger avalanches on this layer.
