The weak layers deep in the snowpack awoke Monday night, resulting in very large avalanches in very skiable terrain.
Minimize your overhead exposure, especially during periods of direct sunshine on steep slopes above.
Multiple persistent weak layers in skiable terrain awoke with Monday's storm. The Jan 11 surface hoar, New Years facets, and the Dec 1 crust/facet combo all were active during rapid loading from winds and snowfall, resulting in very large avalanches.
40-50cm of snow with warm temps and strong, gusty winds built a storm slab. A natural cycle at all elevations started around noon Monday. In many cases on the W side of Rogers Pass, these slabs stepped down into deeper layers.
Some strong sun, some snow, then an alpine temp inversion for the weekend.
Tonight: Mainly clear, Alp low -10*C, light winds
Wed: Sun and cloud, Alp high -9*C, light SW winds
Thurs: Snow, 15cm, Alp high -6*C, strong gusty SW winds
Fri: Cloudy with isolated flurries, Alp high -7*C, light/mod W winds
40-50cm of new snow, warm temps, and strong S'ly winds built a widespread surface storm slab. This sits upon a surface hoar layer at and below treeline, ~50-80cm down, with sugary facets from Xmas below this. Under all this, the Dec 1 crust/facet combo lurks ~2-2.5m below the surface and was woken up by this last storm load.
A large avalanche cycle occurred in the Pass Monday. Numerous sz 4 avalanches, clearing mature timber, were observed on the W side of the Pass. Deep crown lines were observed Tues am, suggesting the deep persistent weak layer from Dec 1 finally couldn't hold the snowload. Fidelity, Camp West, McGill, Smart, Gunners all had big avalanches to sz 3-4.
