Avalanche Forecast
Regions: Kootenay Boundary.
As storm snow settles, be cautious of deeper and more reactive pockets around lee features and open terrain.
Confidence
Moderate -
Weather Forecast
Sunday night: Unsettled with isolated flurries, 5 cm. Moderate and decreasing south wind. Overnight temperatures dropping to -22.
Monday: Cold and cloudy with sunny breaks. Light southwest wind and a high of -16.
Tuesday: Cold, mostly cloudy, and isolated flurries. Light north wind and a high temperature of -20.
Wednesday: Cold, mostly cloudy, and isolated flurries. Light north wind and a high temperature of -20.
Avalanche Summary
On Saturday, storm snow was touchy and reactive to skiers, easily triggering soft slabs 10-40 cm deep. In areas with more wind, slab reactivity and propagation increased through the day in leeward features. Several natural storm slab avalanches size 1-1.5 were also reported.
On Friday, small (size 1-1.5) slab avalanches were reactive to skiers. Explosives triggered larger (size 2.5) avalanches including 2 avalanches which failed on the early December crust with crowns 80-120 cm deep.
On Thursday, several natural and skier-controlled storm slab avalanches up to size 2 were reported, and explosives triggered slab avalanches to size 2.5; avalanches ranged from 20-60 cm deep.
Snowpack Summary
Recent storm totals reached over 100 cm! Cold temperatures will keep snow light and fluffy, but snow will be redistributed easily with any wind. The recent snow reportedly covered a thin freezing rain crust and a surface hoar interface, which has been responsible for recent storm slab avalanches. For now, we don't expect the new snow to bond well to the old interface. Sluffing is to be expected in steep terrain.
A crust from early December is now 50-120 cm below the surface, and is found up to 2300 m. A layer of weak facets (sugary snow) has been reported above and below this crust, and is the layer of concern in our persistent avalanche problem.
The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-300 cm.
Terrain and Travel
- Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
- Start with conservative lines and watch for clues of instability.
- Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
Avalanche Problems
Storm Slabs
Southwesterly winds in the storm created deeper and more reactive pockets in leeward features.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 1 - 2
Persistent Slabs
A crust from early December is now 50-120 cm below the surface, and found up to 2300 m. A layer of weak facets (sugary snow) has been reported above and below this crust. Explosives have triggered large (size 2.5) avalanches failing on this layer as recently as Friday, Dec 24. New snow and wind loading, or a heavy trigger such as a skier or snowmobile, may add enough stress to trigger a persistent slab.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Unlikely - Possible
Expected Size: 2 - 3