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Avalanche Forecast

Archived

Nov 28th, 2024–Nov 29th, 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, South Rockies, East Purcell, Bull, Crowsnest North, Elkford East, Elkford West.

Weak layers in the snowpack warrant careful terrain choices and watching for signs signs of instability like cracking or whumpfing.

Confidence

Low

Avalanche Summary

A size 1 deep persistent slab, 30–40 cm thick, was human-triggered below treeline on Tuesday. Last weekend, several natural and human-triggered slab avalanches (size 1 to 2) occurred near Invermere, mainly on north aspects. These avalanches failed on weak facets near the base of the snowpack.

Observations from the South Rockies are limited.

Smaller wind slab avalanches could step down to basal facets, triggering larger avalanches.

Snowpack Summary

Up to 15 cm of new snow fell over the weekend. A surface hoar layer, 30 to 40 cm deep, is present on shaded slopes and atop a thin crust on sunny slopes. Near the base of the snowpack, a crust with weak sugary facets above and below caused large avalanches last weekend. Snowpack depths at treeline range from 50 to 70 cm.

Most observations are from the Invermere area, but similar conditions are likely in the South Rockies.

Weather Summary

Thursday Night

Mostly cloudy. 10 to 30 km/h west ridgetop wind. Treeline temperature -12 °C.

Friday

Mostly cloudy with up to 1 cm of snow. 30 to 40 km/h west ridgetop wind. Treeline temperature -10 °C.

Saturday

Mix of sun and cloud. 30 km/h west ridgetop wind. Treeline temperature -8 °C.

Sunday

Mostly cloudy with up to 1 cm of snow. 30 km/h west ridgetop wind. Treeline temperature -8 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep terrain, including convex rolls, or areas with a thin, rocky, or variable snowpack.
  • Be careful with wind-loaded pockets, especially near ridge crests and rollovers.
  • Use caution above cliffs and terrain traps where even small avalanches may have severe consequences.

Problems

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.

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.