Avalanche Forecast
Issued: Dec 19th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Avoid wind loaded areas where human triggering remains a concern. If winds pick up today, watch for wind transport creating fresh, reactive wind slabs.
A buried persistent weak layer continues to warrant careful terrain selection and diligent decision making.
Summary
Confidence
Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Sunday Overnight: High pressure will continue to strengthen into the evening. Light northerly winds and clear skies. Temperatures dropping to -15 C in the alpine.Â
Monday: Mainly clear skies with alpine temperatures around -12 C. Light west winds at ridgetop.
Tuesday: Overnight temperatures dropping to around -20 C. Mainly clear with moderate west winds at ridgetop. Temperatures rising with an alpine high of -12 C. Cloud cover increasing into the evening.
Wednesday: Mainly cloudy with flurries, 3-15 cm accumulation. Moderate to strong southwest winds at ridgetop. Alpine temperatures around -8 C.
Avalanche Summary
On Saturday, operators reported several natural and human triggered storm slab avalanches up to size 1 in the alpine and treeline.
Snowpack Summary
Saturday's storm brought 10-30 cm of new snow to the region. On Saturday afternoon, warm temperatures created a thin rain crust on the snow surface in the Nelson and Kootenay Pass area. 3-10 cm of snow overlies this thin crust. In wind exposed areas strong southwest wind has been the dominant feature, transported the new snow into wind slabs in lee features.Â
Below this new snow, last week's storm snow overlies a layer of more consolidated snow over a substantial crust that formed in early December. This crust is 10cm thick on average and is present across all aspects to at least 2300m. A layer of weak facets (sugary snow) has been reported above this crust in Kootenay Pass and the Whitewater backcountry, and likely exists in other areas. This problem is particularly hard to predict and tricky to manage. For this reason wide, conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog.Â
The lower snowpack is composed of several early season crusts. Snow depths at treeline average 150-200 cm. Below 1800m the snowpack remains relatively shallow with 80-120cm on average. The deepest snowpack can be found in the Kootenay Pass area.
Terrain and Travel
- Be careful as you transition into wind affected terrain.
- 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.
Problems
Wind Slabs
Saturday's storm brought 10-30cm of new snow to the region. Moderate southwest winds redistributed this new snow into wind slabs in the alpine and treeline. If the winds do pick up today, there is a lot of snow available for transport, and will create fresh, reactive wind slabs.
In the Whitewater area, surface hoar has been reported below the new snow. This will make slabs more widespread and increase the reactivity and propagation potential. Be suspicious of any areas treeline and below where a slab exists, especially in sheltered areas where this surface hoar may be preserved.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 50-120 cm over a crust that formed in early December. This layer is starting to produce avalanches across the province and this storm may be the tipping point to start seeing both natural and human triggered large destructive avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Dec 20th, 2021 4:00PM
