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Avalanche Forecast

Archived

Dec 18th, 2024–Dec 19th, 2024

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
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, Dogtooth, East Purcell.

Buried weak layers may become more reactive with recent snow and wind loading. Allow some time for the snowpack to stabilize before entering consequential avalanche terrain.

Confidence

Moderate

Avalanche Summary

On Tuesday, a ski cut triggered a size 1 persistent slab avalanche at 2300 m in a deeper snowpack area near the Purcell Wilderness Conservancy. This failed on the early December surface hoar down 40 cm.

On Monday, a natural size 2 avalanche was reported on an east aspect at 2300 m near Bugaboo Provincial Park. In the Dogtooth, explosives triggered a size 1 avalanche on a north aspect in the alpine which is expected to have failed on the early December weak layer.

Snowpack Summary

Roughly 10 cm of new snow fell Wednesday morning, along with moderate alpine winds.

In the mid snowpack, a weak layer of surface hoar and/or small facets is buried on shaded slopes, while a buried sun crust is found on south-facing slopes. The depths of these layers range from 30 to 50 cm (with the south of the region seeing closer to 30 cm).

Particularly around Invermere, the base of the snowpack consists of weak, faceted snow over a crust formed in late October. This layer is likely present throughout the region, though it has not yet been reported as reactive outside the Invermere area.

Weather Summary

Wednesday Night

Mostly clear. 40 km/h west ridgetop wind. Treeline temperature -8 °C.

Thursday

Mostly sunny. 20 km/h southwest ridgetop wind. Treeline temperature -5 °C.

Friday

Mix of sun and cloud. 20 km/h southwest ridgetop wind. Treeline temperature -3 °C.

Saturday

Mostly sunny. 20 km/h south ridgetop wind. Treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and slopes above cliffs.

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.

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.