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Avalanche Forecast

Archived

Feb 10th, 2020–Feb 11th, 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.

New snow has gradually accumulated over the past week and has been redistributed by winds blowing from a variety of directions. As a result, wind slabs at upper elevations are the main concern.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Monday Night: Cloudy with scattered flurries. Moderate west wind. Alpine high temperatures around -10.

Tuesday: Scattered flurries. Moderate west wind. Alpine high temperatures around -6. Freezing level 1000 m

Wednesday: Mix of sun and cloud and isolated flurries. Light west wind. Alpine high temperatures around -5. Freezing level 1100 m

Thursday: Flurries. Light to moderate southwest wind. Alpine high temperatures around -8.

Avalanche Summary

Sunday's reports showed a few windslab avalanches running to size 1.5 in alpine terrain from a variety of aspects. There was also a report of a natural failure on a northerly aspect at 2500 m in the north of the region.

On Saturday there was a report of remotely triggered (from a distance) wind slab avalanche size 2.5 avalanche at 2350 m on a southeast aspect. The details can be seen in this MIN post. There were also reports of numerous loose dry avalanches running in steep terrain size 1-1.5.

Snowpack Summary

20-40 cm of snow accumulating last week sits over older wind-affected snow at high elevations, or over a widespread melt-freeze or rain crust with a variable upper extent of 1800-2000 metres in elevation. The recent snow has mainly shown reactivity where winds have had a chance to redistribute it into new slabs. A few reports from adjacent regions have shown poor bonding with the buried crust where it exists.

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. Recent reports from the Golden area suggest a positive stabilizing trend. At lower elevations this layer has likely been bridged over by the above-mentioned crust.

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 careful as you transition into wind affected terrain.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.