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.
jleblanc,
Avalanche Canada
Don't let the desire for deep powder pull you into high consequence terrain. Keep making conservative choices at treeline, where a persistent slab problem still exists.
Summary
Confidence
Weather Forecast
An Arctic ridge of high pressure will continue to build into the Interior, bringing clear skies and cold conditions with outflow winds through Monday.
SUNDAY NIGHT: Clearing skies/ Light northwest wind / Low of -20
MONDAY: Sunny / Moderate northwest wind / High of -16
TUESDAY: Increasing cloudiness / Moderate to strong southwest wind / High of -15
WEDNESDAY: Snow 5-15 cm / Strong southwest wind / High -15
More details can be found on the Mountain Weather Forecast.
Avalanche Summary
A widespread natural cycle of storm slabs was observed at all elevations during Saturday's storm, including a few large loose dry avalanches (size 2) running fast. Poor visibility restricted avalanche observations during most of the storm.
A naturally triggered size 2.5 persistent slab avalanche was observed in the Monashees on Wednesday on a West aspect at 2150 m. This avalanche failed on the early December facet/crust combo. It was 100 cm deep, a good example of the high consequence of triggering this layer.
If you go out, make sure to report any observations on the Mountain Information Network.
Snowpack Summary
The storm brought around 30-40 cm of new snow in the region, favoring the southeast areas with up to 50 cm. Significant strong southerly winds have formed touchy storm slabs in alpine and treeline, especially in wind-affected terrain. Many sluffs were skiers triggered in low-density snow on steep slopes.
Below the new snow, the defining feature of the snowpack is a widespread crust that reaches as high as 2200m and now sits 80-150 cm below the surface.
In some places, overlying snow is well-bonded to the crust, but in others, weak faceted grains have been observed above it. The facets above the crust are most prominent at treeline where the crust is thinner.
The recent snow load has increased the likelihood of triggering this weak layer.
Terrain and Travel
- Don't let the desire for deep powder pull you into high consequence terrain.
- Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
- Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Wind Slabs
30-45 cm + of recent snow will be available for wind transport Monday. Northwest circulation will also bring cold temperatures and different wind patterns. Touchy wind slabs will build throughout the day on alpine features and open areas at treeline on slopes that have not seen developing slabs during the previous storm.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
A layer of weak facets (sugary snow) can be found down 80-150 cm near a crust layer that formed in early December. This persistent slab problem has recently been most reactive at TREELINE elevations and is possible to human trigger on some slopes. Avoid likely trigger spots such as steep, convex slopes, with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 20th, 2021 4:00PM
