Avalanche forecast

South Coast

Mar 20 – 21, 2015Avalanche Canada
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Avalanche danger

Sun
Mon
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

The current snowpack structure is atypical for this region, especially at this time of year. Check out this blog post for more details: http://www.avalanche.ca/blogs/VQxmdCUAAJZDmnXn/rainsnowwind

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–4
    In recent days, people have remotely triggered large persistent slab avalanches. The spotty nature of this interface makes it difficult to manage. New snow overloading this weak layer could cause surprisingly large avalanches.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    Recent snowfall has created potentially reactive new storm slabs. Watch for triggering in high elevation lee terrain.

Confidence

Fair - Due to the number of field observations

Weather Forecast

The region will see generally light precipitation on Saturday morning. A weak ridge will develop on Sunday before another system arrives on Monday.  Saturday: About 5cm of snow / Moderate southwest winds / Freezing level at 1500m  Sunday: Mix of sun and cloud / Moderate to strong south winds / Freezing level at 1600m    Monday: 5-10cm of snow / Light southwest winds / Freezing level at 1700m

Avalanche Summary

Over the past week, isolated slab avalanches to size 2 have occurred on persistent weaknesses buried on March 11th. In a few cases, avalanches failed with light inputs such as remote triggers. New snow and wind will create its own mix of reactive surface instabilities, but it will also add load to these deeper, more destructive layers. There's a fair bit of uncertainty as to how the March 11th interface will react to storm loading. That said, I'd resist heading into aggressive higher elevation as any releases on this layer would likely be destructive in nature.

Snowpack Summary

By Saturday morning I'd expect new storm slabs to have formed in response to steady wind, snowfall and warm temperatures prior to the weekend. Cornices may also be fragile. A crust/facet persistent weak layer, buried up to 60 cm down, has started to play up in isolated terrain (see avalanche summary). Avalanche problems associated with this layer may linger for a while with the potential for surprisingly large and destructive avalanches. Below this, the snowpack is reported to be generally well-settled and strong. At lower elevations, the diminishing snowpack is trending isothermal (same temperature throughout).

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