Avalanche Forecast

Archived

Jan 11th, 2021–Jan 12th, 2021

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Fresh snow with strong southwest wind likely means that fresh wind slabs are forming, and they may become increasingly reactive throughout the day.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

MONDAY NIGHT - Mainly cloudy with a few flurries, 5 cm / southwest wind 30-60 km/h / alpine low temperature near -6

TUESDAY - Flurries, 5-15 cm, with another 10-20 cm possible overnight / southwest wind 40-80 km/h / alpine high temperature near -2 / freezing level 1500 m

WEDNESDAY - Mainly cloudy with a few flurries, 5 cm / west wind 60-80 km/h / alpine high temperature near -2 / freezing level 2000 m

THURSDAY - A mix of sun and cloud / northwest wind 10-20 km/h / alpine high temperature near -10

Avalanche Summary

Fresh wind slabs are expected to form during the day on Tuesday may be reactive to human triggers at upper elevations.

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 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. View the MIN report HERE.

Snowpack Summary

Fresh snow and moderate to strong southwest wind may create fresh and reactive wind slabs in open areas.

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 has been sporadic, mostly triggered by large loads such as a wind slab avalanche, 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.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avoid exposure to slopes that have cornices overhead.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.