Avalanche Forecast

Issued: Jan 8th, 2021 4:00PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

JSmith, Avalanche Canada

South Rockies.

Sporadic large natural persistent slab avalanches have recently been reported in this region. This low likelihood, high consequence scenario is best avoided by choosing conservative terrain away from overhead hazard.

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

FRIDAY NIGHT: Clear / Light, southwest ridgetop wind / alpine low temperature -18 / Freezing level valley bottom.

SATURDAY: Mix of sun and cloud / Light, southwest ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

SUNDAY: Mix of sun and cloud / Moderate, west ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.

MONDAY: Mostly cloudy / Moderate, northwest ridgetop wind / alpine high temperature -6 / Freezing level 1200 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 ia an example of the "low probability; high consequence" scenario that persistent slab problems often create. MIN report HERE.

Explosive avalanche control produced a few size 2-3 wind slab avalanches on Tuesday. Last weekend there were numerous natural size 2-3 slab avalanches. Most of these were storm slab avalanches in alpine terrain, although some of the reports from the upper Elk Valley included avalanches at treeline elevations that likely failed on 60-100 cm deep surface hoar layers.

Snowpack Summary

Lingering wind slabs formed by recent snow and wind remain possible to human trigger in isolated areas. 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 occurring during natural avalanche cycles. However, this snowpack structure is always a concern for human triggering; especially on steep, rocky slopes with a shallow or thin to thick snowpack.

Terrain and Travel

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

Lingering wind slabs remain possible to human trigger in isolated areas. 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

Possible

Expected Size

1 - 2

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

Unlikely - Possible

Expected Size

2 - 3

Valid until: Jan 9th, 2021 4:00PM