Avalanche forecast

Kootenay Boundary

Mar 18 – 19, 2012Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Danger ratings could be a notch higher is there is prolonged sunshine on Monday.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Fresh wind slabs are forming on lee and cross-loaded features in response to new snow and loading by SW winds. Old wind slabs are now buried but could enhance the size of potential releases on a variety of aspects in exposed areas.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–6
    Cornices are very large and may fail with daytime warming, especially with sunny breaks. There is potential for triggering deep slabs on underlying slopes.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–7
    The deep nature of the mid-February surface hoar layer makes potential avalanches triggered on this layer large and destructive.

Confidence

Fair - Forecast snowfall amounts are uncertain

Weather Forecast

Monday: Unsettled conditions with flurries or periods of snow, and possible sunny breaks (2-5cm). The freezing level should be around 1000-1200m. Winds will be moderate and gusty from the SW. Tuesday: Light to moderate snow - 5-15cm. The freezing level is around 1000m during the day and valley bottom overnight. Winds are moderate to strong from the SW. Wednesday: Unsettled conditions with cloudy skies and light flurries. The freezing level is around 800-1000m. Winds ease to light from the SW.

Avalanche Summary

Recent avalanche activity includes one Size 2 accidentally triggered avalanche. It occurred in relatively well-supported treed terrain on a north aspect. The skier triggered the avalanche in a shallow rocky area. There was also a report of a Size 3.5 avalanche on Saturday that was remotely triggered by a snowcat. This occurred just north of the region in the southern Purcells. It highlights the potential for triggered very large and destructive avalanches. Other observations on Saturday include several loose snow avalanches up to Size 2 on all aspects and skier controlled or explosive controlled avalanches up to Size 2 with 10-150cm deep crowns.

Snowpack Summary

Rain fell to around 2000 m on Thursday afternoon and froze into a crust on all aspects below this elevation. 10-30cm of new snow now sits above the crust. The previous storm snow overlies a sun crust on southern aspects and maybe a spotty 2-6mm surface hoar on north and east aspects, down around 60cm. Below that, the more significant early February surface hoar is down 80-140cm. Snowpack tests show moderate to hard forces generating sudden planar shears on this layer. Below the early February surface hoar layer, the snowpack is strong in most places. Cornices are growing and would act as a significant trigger for all the layers mentioned above if they drop.

Regions covered