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Avalanche Forecast

Archived

Dec 16th, 2020–Dec 17th, 2020

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

Regions

Banff Yoho Kootenay.

We are at a tipping point as far as avalanche danger, and if there is wind in your area Thursday, avalanche activity will increase. Factor this into the terrain you decide to go into.  Really good ski quality for this time of year.

Weather Forecast

Continued light snow Thursday (5-10cm) accompanied by moderate to strong south-westerly winds in the alpine. Valley bottom temperatures around -5 and ridge-top temperatures around -12 to -15. Continued winds increasing to extreme into the weekend including 20-40cm expected in some areas by the end of Sunday.

Snowpack Summary

The dominant issue in the snowpack is the 20-30 cm of low density storm snow and 20-25 cm of loose facets overtop of the Dec 7th layer of sun crust, facets or surface hoar. Continued winds are continuing to create fresh wind slabs in open terrain. Basal facets and crust are present and most pronounced in shallow areas.

Avalanche Summary

Lake Louise and Sunshine ski resorts report small ski-cut and explosive triggered wind slab and loose dry avalanches up to size 1.5. Lots of reports of alpine natural avalanches up to size 2.5 in the last 24 hours. A mix of wind slabs and loose dry avalanches likely triggered anytime the winds picked up. 

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Problems

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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.