Strong winds and new snow will continue to build upon already reactive windslabs and maintain an elevated danger rating.
Adopt terrain travel strategies that avoid steep transitional 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 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.
On Tuesday, a small skier-triggered persistent slab avalanche was reported near Kispiox. This avalanche occurred at treeline and failed on a weak layer of surface hoar sitting on a firm wind-packed surface. Several natural wind slab avalanches were also observed throughout the region, mainly in the alpine (size 1-2).
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.
Thursday night
Mainly cloudy with light snowfall, trace amounts to 3 cm of accumulation. Alpine temperatures slowly rise to -8 °C. Ridgetop wind southwest maintains between 70 to 90 km/h. The freezing level rises to 500 m.
Friday
Cloudy with snowfall, 5 cm of accumulation. Alpine temperatures reach a high of -4 °C. Ridge wind southwest 30 km/h gusting to 75 km/h. Freezing level 400 m.
Saturday
Cloudy with snowfall, 5 to 10 cm of accumulation. Alpine temperatures reach a high of -2 °C. Ridgetop wind southwest 75 km/h gusting to 100 km/h. The freezing level is expected to rise to 1500 m.
Sunday
Cloudy with light snowfall, up to 5 cm of accumulation. Alpine temperatures cool to -9 °C. Ridgetop wind southwest easing to 30 km/h. Freezing level 500 m.
More details can be found in the Mountain Weather Forecast.
