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Avalanche Forecast

Archived

Nov 30th, 2024–Dec 1st, 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.
Below Treeline
Natural avalanches unlikely.

Regions

Banff Yoho Kootenay, Little Yoho, Banff, East Side 93N, Kootenay, Lake Louise, LLSA, Sunshine, West Side 93N, Field.

Elevated winds and a weak faceted snowpack may increase loose dry avalanche activity in steep terrain.

The deep persistent layer remains a major concern on large alpine slopes

Confidence

Moderate

Avalanche Summary

On Saturday, we received several reports of reactive wind slabs forming on immediate lee slopes in the alpine. These small avalanches have been entraining the heavily faceted snowpack in steep terrain.

Over the past week, we've observed several avalanches, both natural and explosive-triggered, reaching up to size 2 on the deep persistent layer. The common factor among these avalanches has been their occurrence on north aspects in the alpine.

Snowpack Summary

In general, we are still dealing with an early-season snowpack, measuring 50-90 cm at treeline. Strong to extreme winds have created a heavily wind-affected upper snowpack in the alpine. The main layer of concern remains the October crust near the ground, where facets and depth hoar are developing. Overall, the snowpack is losing its support and cohesion due to facet development.

Weather Summary

A gradual warmup will persist into the start of the week, with daytime highs reaching -3°C in the alpine by Tuesday. Flurries Sunday will only amount to a trace of snow accumulation. Strong alpine winds are expected to continue Sunday.

Terrain and Travel Advice

  • Be aware of the possibility for full depth avalanches due to deeply buried weak layers.
  • Avoid freshly wind-loaded terrain features.

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.