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Avalanche Forecast

Archived

Nov 26th, 2019–Nov 27th, 2019

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

Regions

South Rockies.

Avalanche danger will increase as an intense winter storm hits the eastern slopes of the Rockies.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

TUESDAY NIGHT: Flurries with accumulations of 10-15 cm of snow on the Alberta side of the continental divide, less in BC, 50-70 km/h wind from the northeast, alpine temperatures drop to -17 C.

WEDNESDAY: Flurries continue throughout the day with another 10-30 cm of snow, 50-80 km/h wind from the northeast, alpine temperatures around -17 C.

THURSDAY: Flurries on Wednesday night bring another 5-20 cm of snow then flurries ease and skies clear by Thursday afternoon, 20-40 km/h wind from the northeast, alpine temperatures around -15 C.

FRIDAY: Sunny, light wind from the northeast, alpine temperatures around -12 C.

Avalanche Summary

The current storm will likely cause a cycle of natural avalanches on Wednesday and/or Thursday. The greatest danger will be in areas that receive the greatest accumulations of new snow, which will likely be the eastern slopes of the Rockies. Human triggering will also be very likely in these area.

Prior to the storm, no avalanches were reported in the South Rockies region, however small wind slab avalanches have been reported in the neighbouring Lizard Flathead, Kananaskis, and Banff regions (see this MIN report for an example).

Snowpack Summary

An intense storm will rapidly change the snowpack. 30-50 cm of new snow is possible by Wednesday afternoon. Strong wind will scour some terrain features down to rocks and old crusty snow while creating extra deep deposits on other terrain features. The new snow is falling on a highly variable early season snowpack. Some alpine terrain already has 50-100 cm of snow while other alpine terrain features and lower elevations have had no snow prior to this storm. In areas that had prior snow, there could be a crust in the snowpack that could act as a sliding layer for the snow above it. Because of the uncertainty about the snowpack structure it is best to avoid or be extremely cautious travelling in avalanche terrain during the storm.

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.