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Avalanche Forecast

Archived

Feb 1st, 2020–Feb 2nd, 2020

Alpine
Natural avalanches possible, human triggered probable.
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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

While refrozen surfaces at lower elevations pose little avalanche hazard, large avalanches may be triggered in areas with wind-drifted new snow at higher elevations. Be prepared to assess conditions and adjust your travel as you gain elevation.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Saturday night: Decreasing cloud, scattered flurries with 2-5 cm of snow, moderate west winds, alpine temperature -10 C.

Sunday: Mostly clear, light northwest winds, alpine high temperature -8 C.

Monday: Partly cloudy, isolated flurries with trace accumulations, light northwest winds, alpine high temperatures -8 C.

Tuesday: Increasing cloud, light southwest wind, alpine high temperature -8 C.

Avalanche Summary

During the storm, numerous large (size 2-2.5) storm slab avalanches were reported in the region. They released naturally as well as from human and explosive triggers. These avalanches occurred on all aspects, mainly at treeline and alpine elevations. Reports indicate that cornices may be reaching their breaking point and may act as triggers for these avalanches. Below tree line, small wet loose avalanches were releasing naturally on Saturday. 

Over the past week, there have been several deep persistent slab avalanches reported in the region. Two were triggered by explosives and 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. Easier-to-trigger storm slab avalanches or cornice fall may have the potential to step-down to this layer.

Snowpack Summary

30-50 cm of storm snow has accumulated at upper elevations (generally above 1900 m). Higher snow totals fell in the northern and western parts of the region. Strong southwest winds have drifted the snow into deeper, stiffer slabs in wind-exposed areas and have rapidly loaded cornices. During a warming event Saturday night, rain saturated snow surfaces up to around 1900 m that have since refrozen with cooling temperatures.

A weak layer of surface hoar may still be found about 90 cm deep around Golden and Kimberley, 50 cm deep around Invermere, and 130 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. New snow, rain, and warming will collectively add considerable strain to these weak layers. Their potential to fail naturally and produce large, destructive avalanches will be significantly increased during the storm.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Remember that the snowpack will be significantly different at higher elevations than lower down.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.

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.