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Avalanche Forecast

Archived

Feb 1st, 2020–Feb 2nd, 2020

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

Regions

Banff Yoho Kootenay.

Rapid loading has created fresh slabs and cornice growth and has overloaded the persistent and deep persistent layers at upper elevations while rain has weakened the snowpack at lower elevations. A widespread natural avalanche cycle has been observed

Weather Forecast

After 24hrs of rain to 2000m, temperatures have begun to drop late in the day Saturday and are expected to reach -10C in valley bottoms overnight. Mountain top winds will diminish to strong values while precipitation will fade to light flurries through mid day Monday before some clearing can be expected.

Snowpack Summary

Wind and storm slabs have developed with strong SW winds, 30 to 70 cm of snow above 2000m. Rain has soaked the snowpack at lower elevations.  The Dec 31 layer of facets, surface hoar and sun crust  is currently down 40-100 cm. The deep persistent basal layer sits 20 to 40 cm above the ground and is more developed in shallow snowpack areas.

Avalanche Summary

A widespread avalanche cycle to sz3.5 has been observed along the roadways of the 3 national parks today. Large wet piles of debris have bee observed to the tops of run outs and bottom of tracks. Although start zones have largely been obscured, involvement of the persistent and deep persistent layers has been seen along the flanks of several events

Confidence

Due to the number of field observations

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.

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.

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.