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Avalanche Forecast

Archived

Jan 28th, 2020–Jan 29th, 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, 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

Purcells.

Wind slabs may be reactive at higher elevations. A deep persistent slab problem still exists at upper elevations and has been responsible for a few recent large avalanches.

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 / southwest wind, 20-30 km/h / alpine low temperature near -8

WEDNESDAY - Cloudy with sunny periods and isolated flurries, up to 5 cm / southwest wind, 40-60 km/h / alpine high temperature near -6 / freezing level 1200 m

THURSDAY - Flurries, 5-10 cm / southwest wind, 40-50 km/h / alpine high temperature near -4 / freezing level 1100 m

FRIDAY - Flurries, 10-15 cm / southwest wind, 20-40 km/h / alpine high temperature near -2 / freezing level 1700 m

Avalanche Summary

On Sunday there were three deep persistent slab avalanches reported in the region. Two were triggered by explosives, but one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer.

Since Thursday, there have been a few reports everyday of natural, human and explosives triggered storm slab and wind slab avalanches up to size 3, but mostly around size 2. These have occurred on all aspects, mainly at treeline and alpine elevations. The peak of this activity occurred on Saturday and has been tapering since. Wind loaded areas at treeline and in the alpine remain the most likely places to trigger an avalanche.

Snowpack Summary

About 5 cm of new snow on Wednesday will sit on the previous 15-30 cm of recent storm snow. Strong southwest winds and warm temperatures on Wednesday will continue to promote wind slab development. Below about 1500 m the snow surface may exist as either a melt-freeze crust, or wet snow.

A weak layer of surface hoar can be found about 70 cm deep around Golden and Kimberley, 30 cm deep around Invermere, 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.
  • Conditions may have improved, but be mindful that deep instabilities are still present.

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.