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Avalanche Forecast

Archived

Feb 3rd, 2020–Feb 4th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Purcells.

Avalanche hazard exists where the wind has loaded cornices and drifted recent snow into wind slabs. Give cornices a wide berth and assess for wind slab conditions before committing to terrain.

Confidence

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

Weather Forecast

Monday night: Clear, light northwest winds, alpine temperature -18 C.

Tuesday: Increasing cloud, light west winds, alpine high temperature -11 C.

Wednesday: Cloudy, 2-5 cm of snow, light southwest winds gusting at ridge-top, alpine high temperature -8 C.

Thursday: Cloudy, scattered flurries with trace accumulations, light west winds, alpine high temperature -6 C.

Avalanche Summary

During the storm, numerous size 2-3.5 slab avalanches released naturally. A few were thought to have stepped down to deeper layers. These avalanches primarily occurred on leeward aspects 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, wet loose avalanches were releasing naturally during the warm temperatures on Saturday. 

With continuous stormy weather over the past week, there have been several deep persistent slab avalanches reported in the region. Most were triggered by explosives and one was remotely human-triggered near Golden. 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 wind slab avalanches or cornice fall may have the potential to step-down to this layer.

Snowpack Summary

There have been substantial changes to the snowpack over the past few days. 40-60 cm of snow fell during the weekend storm above 1900 m. Higher snow totals fell in the northern and western parts of the region. Extreme winds originating from the southwest and shifting to the northwest have created a tricky loading pattern at treeline and above and have elevated concern for cornice triggers. These winds have drifted the snow into slabs on leeward terrain features that may remain prone to human triggering. During a warming event Saturday night, rain saturated snow surfaces up to around 1900 m that have since formed a crust.

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. It remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall. 

Terrain and Travel

  • Be aware of highly variable recent wind loading patterns.
  • Stay off recently wind loaded slopes until they have had a chance to stabilize.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger 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.