Regions
Kootenay Boundary.
Recently formed wind slabs are the main concern and are expected to be touchy on Wednesday. Loose dry avalanches are also a concern in steep terrain.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
Mostly cloudy conditions are expected on Wednesday with the potential for both light flurries and sunny breaks. Alpine wind is forecast to be moderate to strong from the west to northwest directions. Treeline temperatures are expected to be around -10C. The next storm front is forecast to arrive on Thursday morning. 5-10cm of snowfall is forecast by Thursday evening with another 5-10cm Thursday overnight. Alpine wind is expected to be strong from the southwest and treeline temperatures are forecast to be around -8C. Friday is currently forecast to be dry and sunny.
Avalanche Summary
On Tuesday, numerous natural slab avalanches up to size 2 were reported at treeline in the Whitewater area. Several natural loose dry avalanches up to size 1.5 were also observed on steep southerly aspects at 1700-2100 m elevation in the Kootenay Pass area. Explosives triggered storm slab avalanches up to size 2 at 1800-2100 m elevation which were reported as soft slabs and likely around 30cm thick. On Wednesday, wind slabs are expected to be the main concern. Ongoing strong southerly winds are redistributing the 20-30 cm of new snow from Tuesday. Where the new snow remains unconsolidated, loose dry avalanches from steep terrain are expected to be the main concern.
Snowpack Summary
30-40 cm of low density snow accumulated during the storm on Monday night. The new snow sits over wind scoured surfaces or old wind slabs in exposed terrain and surface hoar up to 5 mm in sheltered areas. In exposed terrain, strong southerly winds have redistributed the new snow and wind slabs exist in leeward terrain features. A freezing rain crust from last week is now down around 60 cm and reports suggest it is generally not creating an instability. The mid-December interface is now down 70-100 cm. While test results suggest it still may be reactive in isolated areas, the layer is generally considered dormant.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Loose Dry
Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.