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Avalanche Forecast

Archived

Jan 22nd, 2020–Jan 23rd, 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.

Recent fresh snow has been redistributed into pockets of wind slab at tree line and in the alpine. Use caution in wind exposed terrain.

Confidence

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

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy with isolated flurries / southwest wind, 20-30 km/h / alpine low temperature near -8

THURSDAY - Cloudy with scattered flurries, up to 5 cm / southwest wind, 30-50 km/h / alpine high temperature near -3 / freezing level 1300 m

FRIDAY - Cloudy with scattered flurries, up to 5 cm / southwest wind, 20-30 km/h / alpine high temperature near -2 / freezing level 1500 m

SATURDAY - Mainly cloudy with scattered flurries / southwest wind, 20-30 km/h / alpine high temperature near -5 / freezing level 1400 m

Avalanche Summary

With strong winds and some fresh snow in the forecast, there could be new wind slabs forming on Thursday and they may become increasingly reactive throughout the day.

Over the past three days there have been a few reports of natural and explosives triggered avalanches up to size 3. A few of these were deep persistent slab avalanches that failed near the base of the snowpack.

There have been no reports of human triggered avalanches over the last three days.

Snowpack Summary

Around 15-20 cm of recent snow over the past week and strong southwest wind has produced wind slabs in lee terrain features. Strong southwest winds on Thursday may form fresh and potentially reactive wind slabs at upper elevations.

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

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • 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.