Avalanche Forecast
Issued: Jan 10th, 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.
JSmith,
Avalanche Canada
Large naturally triggered persistent slab avalanches failing on a deeply buried crust have recently been reported. Human triggering of this layer is most likely on steep, rocky terrain with a shallow or thin to thick snowpack.
Summary
Confidence
Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.
Weather Forecast
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SUNDAY NIGHT: Mostly cloudy / Moderate, west ridgetop wind / alpine low temperature -13 / Freezing level valley bottom.
MONDAY: Cloudy with isolated flurries; 0-3 cm. / Strong, west ridgetop wind / alpine high temperature -6 / Freezing level 1400 m.
TUESDAY: Flurries; 3-5 cm. / Extreme, southwest ridgetop wind / alpine high temperature -2 / Freezing level rising to 1900 m.
WEDNESDAY: Snow; 5-10 cm. / Moderate, west ridgetop wind / alpine high temperature -5 / Freezing level 1500 m.
Avalanche Summary
A large (size three) cornice triggered persistent slab avalanche was reported on a large south facing alpine slope in the Crowsnest Pass area on Thursday. This avalanche failed on a weak facets overlying a hard crust deep in the snowpack and is an example of the "low probability; high consequence" scenario that persistent slab problems often create. MIN report HERE.
Snowpack Summary
Recent extreme westerly winds continue to build larger and more fragile cornices which have recently triggered large avalanches when they fail. Fresh wind slabs have also formed in open terrain at treeline and above that may be possible to human trigger. The upper snowpack consists of several layers of old wind slabs, while the lower snowpack consists of decomposing crusts and weak faceted snow. In the Elk Valley, a decomposing surface hoar layer can be found around one of these crusts 50-100 cm below the surface. Avalanche activity on these layers in the lower snowpack have been sporadic, mostly triggered by large loads such as a wind slab in motion or a cornice fall. These deeper weak layers are most likely to be human triggered on steep, rocky slopes with a shallow or thin to thick snowpack.
Terrain and Travel
- Be carefull around freshly wind loaded features.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
- Avoid exposure to slopes that have cornices overhead.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Wind Slabs
Strong winds may form fresh wind slabs throughout the day on lee features at treeline and above. Wind slabs in motion may step-down to deeper weak layers resulting in large avalanches.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Triggering large avalanches on weaknesses in the lower snowpack remains a possibility. In some areas the concern is weak snow around crusts 50 to 100 cm deep, while in others it's weak snow near the bottom of the snowpack. Human triggering of these layers are most likely in steep, rocky slopes with a shallow or thin to thick snowpack.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Jan 11th, 2021 4:00PM
