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Avalanche Forecast

Archived

Jan 24th, 2020–Jan 25th, 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.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Fresh wind slabs in exposed areas will be the primary concern for Saturday, so seek out sheltered low density snow. Recent snowfalls varied widely across the region, so make local observations of new snow depth to determine the scale of the wind slab problem in your area.

Confidence

Moderate -

Weather Forecast

Friday night: Cloudy with scattered flurries bringing up to 5 cm of new snow. Light west winds.

Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light southwest winds, becoming moderate at ridgetop. Alpine high temperatures around -5 with freezing levels to 1400 metres.

Sunday: Cloudy with light flurries beginning in the afternoon. Light to moderate southeast winds. Alpine high temperatures around -5.

Monday: Cloudy with isolated flurries and a trace of new snow. Light southwest winds. Alpine high temperatures around-5.

Avalanche Summary

Reports from Thursday showed ski cuts producing small (size 1) 20-25 cm-deep storm slab releases in the south of the region. Further north in the Golden area where less new snow exists, ski cuts produced numerous smaller 2-5 cm-deep wind slab releases.

On Wednesday, a few deep persistent slab avalanches were reported in the Purcells west of Invermere. These were triggered by skier traffic, ski cutting, and remotely from a group traveling nearby. They ranged from size 1-2, with the smaller example being a wind slab that reloaded the basal snowpack where it had already avalanched. The larger two had 100 cm-deep crown fractures.

Over the past week there have been a few other reports of natural and explosives triggered avalanches reaching size 3. A few of these were also deep persistent slab avalanches that failed near the base of the snowpack.

Snowpack Summary

Light snowfalls over the past week brought around 15-20 cm of snow to the region. Bouts of strong southwest wind over the same period formed new wind slabs on leeward slopes at higher elevations while warm temperatures caused surface snow to melt below about at least 1500 metres and in some areas created moist snow up to 2000 metres.

A layer of surface hoar that formed in late December appears to be gaining strength. It can be found 70 cm deep around Golden, 30 cm deep around Invermere, 70 cm deep around Kimberley, and 100 cm deep along Kootenay Lake.

As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives.

Terrain and Travel

  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.

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.