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Avalanche Forecast

Archived

Nov 27th, 2024–Nov 28th, 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.

Wind slabs and a deep persistent slabs continue to be reactive to rider triggers. Start conservative and watch for signs of instability like cracking or whumpfing.

Confidence

Low

Avalanche Summary

The deep persistent slab was reactive to rider triggers up to size 1 on Tuesday below treeline.

Last weekend, numerous natural and human-triggered persistent slab avalanches (up to size 2.5) were observed near Invermere. These primarily occurred on north through southeast aspects at treeline and above.

Smaller wind slab avalanches could step-down to the basal facets, initiating a larger slab avalanche.

Snowpack Summary

Up to 15 cm of new snow fell over the weekend. In wind-exposed areas cracking and whumping have been reported.

Down 30 to 40 cm sits a layer of surface hoar primarily found on shaded slopes, or on a thin crust on sunny slopes.

A crust exists near the bottom of the snowpack. This crust may have weak, sugary facets above and below it. Large avalanches failed on this layer last weekend.

Snowpack depths are reported to be 50-70 cm at treeline elevation.

Weather Summary

Wednesday Night

Cloudy with isolated flurries. 15 to 35 km/h west ridgetop wind. Treeline temperature -10 °C.

Thursday

Mix of sun and cloud. 10 to 30 km/h west ridgetop wind. Treeline temperature -9 °C.

Friday

Mix of sun and cloud. 15 to 30 km/h west ridgetop wind. Treeline temperature -10 °C.

Saturday

Mix of sun and cloud. 20 to 30 km/h west ridgetop wind. Treeline temperature -10°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.
  • Be careful with wind-loaded pockets, especially near ridge crests and rollovers.
  • 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.