Assess how the new snow is bonding to underlying layers, especially in wind-loaded areas.
A buried persistent weak layer means avalanches could step down and become larger than expected.
New snow overlies a variety of surfaces, including surface hoar, facets, or a crust, which may make wind slabs more reactive and take longer to bond.
Several persistent weak layers exist, with the most problematic ones lying 30 to 60 cm deep. The greatest concern for triggering these layers lies in areas where a thick, supportive crust is absent near the surface.
Thurs: A naturally-triggered deep persistent slab occurred near Invermere, 30-100 cm deep.
Tues: Avalanche control produced large avalanches (up to size 3.5) in the central-western part of the region.
Mon: Extensive avalanche activity with storm and wind slabs, some notably stepping down to deeper persistent weak layers.
Looking forward: We expect both wind slabs and persistent slabs to remain triggerable over the following days.
Up to 25 cm of recent snow has formed fresh wind slabs near ridgetops on leeward north through east facing slopes, driven by southwest winds. The new snow sits on a sun crust on solar aspects, and surface hoar or facets in sheltered areas or north aspects. At lower elevations the snow surface may be moist or crusty. A few weak layers consisting of a crust, facets or surface hoar from February and January remain a concern, buried 30 to 60 cm. A layer of facets from early December is buried 70 to 120 cm. In many areas, facets or depth hoar make up the base of the snowpack.
Thursday Night
Partly cloudy with trace amounts of snow possible. 15 to 30 km/h southwest ridgetop winds. Treeline temperature -10 °C.
Friday
A mix of sun and clouds. 15 km/h southwest ridgetop winds. Treeline temperature -7 °C.
Saturday
A mix of sun and cloud, with isolated flurries up to 2 cm. 10 to 15 km/h south ridgetop winds. Treeline temperature -6 °C.
Sunday
A mix of sun and cloud. 10 to 15 km/h southwest ridgetop winds. Treeline temperature -5 °C.
More details can be found in the Mountain Weather Forecast.
