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Avalanche Forecast

Archived

Dec 7th, 2024–Dec 8th, 2024

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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

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

Up to 25 cm of storm snow in the west, with only a few centimeters in the east, increases the reactivity of storm slabs. This will raise avalanche danger to high, and avoiding avalanche terrain is strongly recommended.

Confidence

Moderate

Avalanche Summary

Lake Louise reported triggering a few size 1 storm slabs with explosives, while Sunshine Patrol noted some size 1 ski cuts near treeline. Otherwise, observations were limited. Once skies clear, evidence of avalanches is expected.

Snowpack Summary

Up to 30 cm of storm snow by Sunday morning is expected to create fresh surface slabs, some of which may fail near the ground. The storm snow will bury a mix of sun crust, wind crust, and facets, sitting atop a faceted snowpack 40–90 cm deep. Two persistent weak layers near the base (the Oct 20 and Nov 9 crusts) continue to produce isolated avalanches and remain a key concern for deeper releases.

Weather Summary

Sunday’s temperatures are forecasted to be -5°C in the valley and -15°C at ridge tops. Up to 15 cm of additional storm snow is expected, bringing totals to around 30 cm on the western side of the region. Saturday’s strong winds will ease to moderate by Sunday, with a high-pressure system building in late Sunday into Monday.

Terrain and Travel Advice

  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.