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Avalanche Forecast

Archived

Jan 21st, 2020–Jan 22nd, 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.

Use caution as you transition into wind exposed terrain. Avalanches are possible where wind slabs have formed.

Confidence

Moderate - Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

TUESDAY NIGHT - Cloudy with clear periods and isolated flurries / southwest wind, 20-40 km/h / alpine low temperature near -8

WEDNESDAY - Cloudy with sunny periods and isolated flurries / southwest wind, 10-25 km/h / alpine high temperature near -8

THURSDAY - Cloudy with sunny periods and isolated flurries / southwest wind, 25-50 km/h / alpine high temperature near -2 / freezing level 1300 m

FRIDAY - Flurries, 5-10 cm / southwest wind, 20-40 km/h / alpine high temperature near -2 / freezing level 1500 m

Avalanche Summary

On Sunday and Monday there were a few natural and cornice triggered avalanches up to size 2.5.

Numerous large (size 2) wind slabs were triggered by humans and explosives on Saturday. They were generally 10 to 40 cm deep and occurred at treeline and alpine elevations.

A couple of deep persistent slabs were triggered by explosives. They were large (size 2) and occurred in the alpine, scrubbing to the ground.

Snowpack Summary

Around 15 cm of recent snow and strong southwest wind has produced wind slabs in lee terrain features, particularly near ridges.

A layer of surface hoar that formed in late December appears to be less reactive than it was a week ago and 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

  • Avoid freshly wind loaded terrain features.
  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.

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.