Strong winds and new snow will continue to build upon already reactive wind slabs and maintain an elevated danger rating.
Adopt terrain travel strategies that avoid steep areas on north-aspect terrain that will certainly harbor new and existing reactive windslabs.
Continuing southerly winds and new snow will form fresh wind slabs in alpine and treeline lee aspect terrain. Watch for changing conditions with aspect and elevation and avoid wind-loaded areas.
Triggering persistent slab avalanches remains possible due to several weak layers in the top metre of the snowpack. Facet layers are the primary concern in alpine terrain, while preserved surface hoar layers are the concern in treeline terrain.
In the north of the region, the lower snowpack remains weak and heavily faceted. Large triggers such as cornice failure or smaller avalanches stepping down to this layer are possible.
Avalanches that start as wind slabs may step down to these deeper layers.
On Thursday, low visibility impeded visual observations., however, numerous audible avalanches have been reported. Additionally, observation of powder clouds pluming out of very steep extreme terrain was reported.
On Wednesday, professional operations reported a natural windslab avalanche cycle of large avalanches (size 3). These avalanches initiated in the alpine, on steep north aspect terrain near ridgetop. Moderate to strong southwest wind loading was the suspected trigger. Due to the size of these avalanches, it is suspected that they had stepped down to the lower/mid-pack PWLs.
The incoming storm events are forecast to bring to the area, strong southerly wind and light snowfall. Expect continued formation of fresh wind slabs. Avoid wind-loaded areas at upper elevations and keep in mind the potential for deeper instabilities to produce large and surprising avalanches.
At upper elevations, southerly winds have scoured windward areas and redistributed past storm snow into wind slabs in lee areas. Windslab depth has been reported up to 50 cm in depth.
Several persistent weak layers may be found in the top meter of the snowpack. Most prominently, a layer of surface hoar buried in early January is now 20-50 cm deep and is reactive to skier traffic. A weak layer of facets and/or surface hoar buried in late December is now down 70-110 cm.
In alpine terrain, triggering one of these layers is most likely on steep rocky slopes where they present as facets. In treeline terrain, the layers are most likely triggered on steep slopes in open trees where they present as preserved surface hoar.
In the north of the region, the lower snowpack remains weak and heavily faceted.
Friday night
Cloudy with snowfall, 5 cm of accumulation. Alpine temperatures reach a high of -2 °C. Ridge wind southwest 100 km/h easing to 40 km/h. Freezing level 1500 m.
Saturday
Cloudy with light snowfall, 1 to 5 cm of accumulation. Alpine temperatures are cooling to -10 °C. Ridgetop wind southwest 40 km/h gusting to 60 km/h. The freezing level is expected to fall to 200 m.
SundayCloudy with light snowfall, up to 5 cm of accumulation. Alpine temperatures -8 °C. Ridgetop wind northwest 60 km/h easing to 30 km/h. Freezing level 400 m.
MondayCloudy with snowfall, 5 cm of accumulation. Alpine temperatures reach a high of -6 °C. Ridge wind southwest 30 km/h gusting to 75 km/h. Freezing level 500 m.
More details can be found in the Mountain Weather Forecast.
