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Avalanche Forecast

Archived

Jan 17th, 2020–Jan 18th, 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.

Pay attention to wind affected snow in exposed terrain, where triggering avalanches is most likely.

Confidence

High -

Weather Forecast

FRIDAY NIGHT: Increasing clouds, light to moderate southwest wind, alpine temperature -15 C, freezing level below valley bottom.

SATURDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, moderate to strong southwest wind, alpine temperature -12 C, freezing level below valley bottom.

SUNDAY: Mix of sun and cloud with isolated flurries, accumulation 1 to 3 cm, moderate southwest wind, alpine temperature -7 C, freezing level 500 m.

MONDAY: Mix of sun and cloud with isolated flurries, accumulationg 1 to 3 cm, moderate southwest wind, alpine temperature -3 C, freezing level 1000 m.

Avalanche Summary

On Thursday and Friday, wind slab avalanches were triggered naturally, by skiers, and explosives. They occurred on north and east lee terrain features, generally at and above treeline. They were 10 to 30 cm deep.

The last deep persistent slabs were reported on Monday and Tuesday. They were large (size 2-3) and were triggered naturally and with explosives in steep alpine terrain. 

It has been over one week since any persistent slab avalanches on the December surface hoar layer have been reported, although there could still be lingering concerns about triggering that layer on isolated slopes in steep treeline clearings.

Snowpack Summary

Surface conditions are variable due to cold temperatures and shifting wind directions over the past few days, but the most recent fresh wind slabs can be found on north and east lee features. 

A layer of surface hoar that formed in late December appears to be less reactive than it was a week ago and 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.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • 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.