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Avalanche Forecast

Archived

Nov 18th, 2021–Nov 19th, 2021

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

Regions

Banff Yoho Kootenay.

The natural cycle has tapered off, but explosive work today triggered numerous avalanches to size 2.5.

Weather Forecast

For Friday expect a mix of sun and cloud, with no precipitation, light winds, and highs around -8C.  For the weekend, the forecast is for light precipitation 5-10 cm with gusty SW winds and highs around -10C.

Snowpack Summary

Several cm of fresh snow exist over a surface crust (below 2100m). Recent storm snow (5 day total of 65-90 cm) is settling. Wind slabs exist in alpine and down into tree-line elevations. A melt/freeze crust and/or facets exist near the ground (in some locations).  Snowpack depths at tree-line average 60-110 cm

Avalanche Summary

Explosive work around Lake Louise, Sunshine, and on Mt Bosworth produced numerous avalanches today to size 2,5.  Most avalanches were windslabs 20-40 cm thick and some failed on the basal facets. It remains likely a person could trigger  or remote trigger an avalanche on steeper slopes that have not yet slid.

Confidence

Due to the number and quality of field observations

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.