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Avalanche Forecast

Archived

Nov 29th, 2024–Nov 30th, 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.

Although we haven't seen the wind increase yet, they are still forecasted to increase to strong Friday night. This may create new windslabs and cause some loose dry avalanches.

The deep persistent problem remains the layer of greatest concern on large alpine slopes.

Confidence

Moderate

Avalanche Summary

Today, sunshine found thin windslabs in steep Northerly terrain that were reactive to explosives. Around Lake Louise, some loose dry avalanches were triggered by explosives in unworked terrain.

In the past week, we have seen several avalanches both natural and explosive triggered up to size 2 on the deep persistent layer. The common theme for these avalanches were North aspects in the alpine in steep or extreme terrain.

Snowpack Summary

10-20 cm of snow from last week lies on an early-season snowpack measuring 50-90 cm at treeline. The main layer of concern continues to be the October crust near the ground, where facets and depth hoar are developing. Overall the snowpack is losing its support/cohesion with facet development.

Weather Summary

Slightly warmer on Saturday with alpine temperatures around-10C. Westerly winds are forecast to increase to strong overnight Friday and into Saturday. Flurries are expected with the greatest amounts in the Northern part of the region (5-10 cm). See the image below for tables.

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.