Avalanche Forecast
Issued: Dec 18th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
zryan,
Avalanche Canada
Saturday's storm created storm slabs in the alpine and treeline that will likely still be reactive to human triggering. Anticipate larger, more reactive slabs in wind loaded areas. Uncertainty exists around a buried persistent weak layer. Learn more about how to manage it here.
Summary
Confidence
Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
Saturday Overnight: Continued snowfall into the evening, another 10-25 cm of accumulation expected, tapering into the morning. Strong southwest winds easing into the morning and shifting west.
Sunday: Mainly clear with light to moderate northwest winds at ridgetop. Alpine temperatures around -11 C.Â
Monday: Partially cloudy with light flurries, trace to 3 cm of accumulation. Winds strengthening throughout the day, moderate west winds at ridgetop in the afternoon. Alpine temperatures around -10 C.
Tuesday: Increasing cloud cover in the afternoon, strengthening west winds, moderate to strong at ridgecrest. Alpine temperatures rising to -8 C.
Avalanche Summary
Natural avalanches releasing in the new snow are likely on Saturday evening, and potentially continuing into the day on Sunday. Storm slab avalanches are expected to be sensitive to human-triggers. Avalanches in the new snow have the potential to step-down to recently reactive weak layers, producing very large, destructive avalanches. Â
On Saturday, operators reported several natural and human triggered storm slab avalanches up to size 1 in the alpine and treeline.
Snowpack Summary
Yesterday's storm brought 20-50cm of new snow to region. Storm slabs are expected to be widespread across all aspects. In wind exposed areas strong southwest wind will have been the dominant feature, transported the new snow into deeper deposits 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. The lower snowpack is composed of several early season crusts.Â
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.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Problems
Storm Slabs
20-50 cm of new snow has fallen since Friday evening. The new snow will likely form a reactive storm slab problem in the alpine and treeline. Anticipate larger, more reactive slabs in wind-drifted areas.
Aspects: All aspects.
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 19th, 2021 4:00PM
