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Avalanche Forecast

Archived

Dec 4th, 2024–Dec 5th, 2024

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

Wind slabs may be reactive in leeward terrain features at higher elevations.

Lingering concern remains for a weak layer near the base of the snowpack which may still be reactive in some areas.

Confidence

Low

Avalanche Summary

On Tuesday, small loose avalanches were reported on steep south aspects.

Last week, several small (size 1 to 1.5) deep persistent slab avalanches were reported in the Invermere area. These 40 cm thick slabs were failing on weak basal snow and have been triggered by both riders and explosives.

Snowpack Summary

Treeline snow depths are generally 50 to 70 cm, with deeper wind-loaded pockets in the alpine. New surface hoar is growing on the surface in sheltered terrain and wind-affected surfaces are expected in exposed terrain at higher elevations. A new sun crust is likely forming on steep, sun-exposed slopes.

In the Invermere area, weak faceted snow at the base of the snowpack has caused several small but notable deep persistent slab avalanches.

Early-season hazards are present at all elevations. Stay alert and assess terrain carefully.

Weather Summary

Wednesday Night

Mainly clear. 10 to 20 km/h southwest ridgetop wind. Treeline temperature near 0 °C with a temperature inversion.

Thursday

Mainly sunny. 10 to 20 km/h southwest ridgetop wind. Treeline temperature near 0 °C with the temperature inversion breaking down through the day.

Friday

A mix of sun and cloud. 20 to 40 km/h southwest ridgetop wind. Treeline temperature -3 °C.

Saturday

Cloudy with snowfall up to 15 cm. 30 to 60 km/h southwest ridgetop wind. Treeline temperature -3 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Be careful with wind-loaded pockets, especially near ridge crests and rollovers.
  • Be mindful that deep instabilities are still present in the snowpack.
  • Triggering deep layers is more likely if the snow surface didn't freeze overnight.

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.