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Avalanche Forecast

Archived

Dec 8th, 2019–Dec 9th, 2019

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

Regions

North Columbia.

There is uncertainty with the reactivity of several buried weak layers. Best to adopt a conservative approach while the snowpack adjusts to the increased load from recent snowfalls.

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

Sunday: Mainly clear with cloudy periods, alpine temperature -9, moderate northwest wind.

Monday: Mix of sun and clouds, alpine temperature -7, moderate north wind.

Tuesday: Mix of sun and cloud, alpine temperature -8, light northwest wind.

Wednesday: Cloudy with flurries, alpine temperature -8, light southwest wind.

Avalanche Summary

Reports from Friday and Saturday indicate skier triggered and natural storm slab avalanches size 1-2 on all aspects. There were also a few reports of persistent slab avalanches failing on a layer of surface hoar down 80-120 cm at treeline elevations over the past several days. At least one of these was remotely triggered (from a distance). Additionally there reports of explosive triggered avalanches to size 3 in the trans Canada highway corridor on Friday.

Snowpack Summary

30-60 cm of new snow from late last week has covered a layer of feathery surface hoar that has been found at all elevations. A thick layer of faceted crystals, previously wind-affected surfaces, and/or surface hoar in sheltered areas (around treeline and below) is now 50-90 cm below the surface.

An additional layer of surface hoar may be found in sheltered areas around treeline down 70-120 cm. In some areas this may sitting on a thin crust.

A variety of crusts from late October are buried deeper in the snowpack.

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.