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Avalanche Forecast

Archived

Nov 26th, 2020–Nov 27th, 2020

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

Kootenay Boundary.

 Watch for reactive wind slabs at upper elevations, and be aware of the potential for larger avalanches due to a crust that was buried in early November. 

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Thursday night: Mostly cloudy, light to moderate northwest wind, freezing level 500 m.

Friday: Mostly cloudy, moderate southwest wind, freezing level 1000 m.

Saturday: Up to 5 cm new snow overnight then clearing, moderate southwest wind, freezing level 500-1000 m.

Sunday: Scattered cloud, light southwest wind, freezing level 700 m.

Avalanche Summary

Small loose avalanches were observed out of steep terrain on Wednesday.

Our eyes and ears in the mountains are limited at this time of year and may continue this winter due to fewer professional observations. If you see anything while out in the field, please consider sharing it with us and fellow recreationists via the Mountain Information Network (MIN). Even just a photo of where you went is helpful. A big thank you to those that have already shared their observations thus far.

Snowpack Summary

The snowpack is deepest in the north of the region and shallowest in the south. Expect to find around 100 to 150 cm at treeline in the north and 50 to 100 cm in the south. 

About 10 to 15 cm of recent snow may have been redistributed by the wind, forming deeper and cohesive deposits in lee terrain features at higher elevations. This recent snow may overly a layer of weak and feathery surface hoar that likely only exists in sheltered terrain features and perhaps only in the south of the region (e.g., Kootenay Pass). 

Melt-freeze crusts from mid- and early-November are generally found 30 cm below the snow surface and 30 cm up from the ground, respectively. Some reports suggest the snow is well-bonded to these crusts but other reports have found unstable conditions, where sugary faceted grains exist above the crust.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Be aware of the possibility for full depth avalanches due to deeply buried weak layers.
  • Be cautious of buried obstacles especially below treeline.

Problems

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.

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.