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Avalanche Forecast

Archived

Dec 9th, 2021–Dec 10th, 2021

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

Regions

Glacier.

Skier triggering of slab and loose dry avalanches is possible. A cautious approach to large features and steep terrain is recommended.

Weather Forecast

Lingering flurries under a weak NW flow Friday will give way to a more organized system from the West into the weekend.

Friday: Flurries (up to 7 cm). Alpine High -11*C. Moderate SW ridgetop winds.

Saturday: Snow (up to 20cm). Low -13*C, High -8*C. Mod gusting Extreme SW wind.

Sunday: Flurries (up to 5cm). Low -15*C, High -11*C, Mod SW wind.

Snowpack Summary

Approximately 30 cm of new snow fell Wednesday with South winds, creating fresh slabs in exposed terrain features, and a loose dry avalanches problem in steep sheltered terrain. The Dec 1st rain crust is ~20cm thick, buried 40cm at 1300m/60cm at TL, and can be found up to 2300m. The mid and lower snowpack is generally well bonded and strong.

Avalanche Summary

On Thursday, a field team triggered two small slab avalanches on the Dec. 1st crust, these both occurred on steep slopes at treeline.

On Wednesday several large avalanches were observed above the highway. The majority of these were in very steep terrain off of Mt Macdonald and Tupper.

Confidence

Due to the number and quality of field observations

Problems

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.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.