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Avalanche Forecast

Archived

Dec 21st, 2024–Dec 22nd, 2024

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

Regions

Purcells, East Purcell, West Purcell.

Choose sheltered, low-consequence terrain. Recently formed wind slabs in combination with buried weak layers necessitate a conservative approach.

Confidence

Moderate

Avalanche Summary

A natural avalanche cycle took place during the storm last Wednesday.

On Thursday, explosive control in the Invermere area produced two size 2 deep slab avalanches from east-facing treeline terrain.

On Friday, one size 1 natural slab avalanche was observed from afar on a north aspect at 2600 m.

Snowpack Summary

Light overnight falls atop 20 cm of recent storm snow with deeper deposits accumulating in lee-facing terrain at higher elevations due to southwest winds.

The mid-snowpack may hold a weak surface hoar or facets layer on shaded slopes and a sun crust on south-facing slopes, buried 20–40 cm deep.

Near Invermere, the snowpack base is weak, with faceted snow over an October crust. This layer likely exists region-wide but has only shown signs of instability near Invermere.

Weather Summary

Saturday Night

Cloudy with up to 5 cm of new snow. 10 to 40 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Sunday

Cloudy with up to 1 cm of new snow. 15 to 30 km/h southwest ridgetop wind. Treeline temperature -5 °C.

Monday

Cloudy with up to 3 cm of new snow. 15 to 30 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Tuesday

Cloudy with up to 2 cm of new snow. 20 to 50 km/h southwest ridgetop wind. Treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep, rocky, and wind-affected 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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.