Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Jan 10th, 2021–Jan 11th, 2021

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
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.

Regions

South Rockies.

  

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.

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

  

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

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.