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Avalanche Forecast

Archived

Dec 19th, 2024–Dec 20th, 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.

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

Confidence

Moderate

Avalanche Summary

On Wednesday after the storm, a few natural wind slabs were observed in the alpine (size 1-2). Observations were limited by poor visibility.

Looking forward to Friday, wind slabs may remain reactive to human triggering at upper elevations. Concern for buried weak layers continues to warrant conservative terrain selection. This means choosing small, low-consequence slopes.

Snowpack Summary

In the past few days, up to 20 cm of new snow fell, accompanied by southwest winds, creating wind slabs and scoured surfaces at alpine and treeline elevations.

The mid-snowpack may hold a weak layer of surface hoar or facets 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

Thursday Night

Cloudy with up to 3 cm of snow. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -7 °C.

Friday

Cloudy with up to 1 cm of snow. 30 to 50 km/h southwest ridgetop wind. Treeline temperature -4 °C.

Saturday

A mix of sun and cloud with isolated flurries. 10 to 30 km/h southwest ridgetop wind. Treeline temperature -3 °C.

Sunday

Mostly sunny. 10 to 40 km/h southwest ridgetop wind. Treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • 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.

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.