Avalanche forecast

South Columbia

Mar 9 – 10, 2016Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
4 · High
Treeline
4 · High
Below
2 · Moderate
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Highlights

A storm will bring high avalanche danger to the South Columbia.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    2–5
    A crust/surface hoar layer buried approximately 70 cm below the surface is triggerable by people on sleds or on skis. This layer could also avalanche naturally during stormy weather and produce large avalanches.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely - Certain
    Size
    1–4
    Avalanches are expected to run in response to loading from new snow and wind, especially on north through east aspects.

Confidence

High

Weather Forecast

Thursday: 15-20 cm new snow expected with the heaviest amounts likely to be in the south of the region. Strong southwest winds up to 80 km/h expected at ridgetop. Freezing levels expected to rise to 1800 m near noon.  Friday: mostly dry with some lingering flurries. Some clearing expected. Winds becoming light southeasterly. Freezing level around 1700 m. Saturday: 5-10 cm new snow, with moderate southwesterly winds and freezing level remaining around 1700 m.

Avalanche Summary

On Tuesday, several slab avalanches were noted on solar aspects in recent storm snow, including one very large size 3 that started on a hanging convex feature at 2400 m and ran all the way to valley bottom. The previous two days before that (Sunday and Monday) had seen an avalanche cycle mostly on northwest to northeast aspects above 1800 m with sizes averaging size 2 and crown depths averaging 50 cm. Most of these avalanches appeared to be initiating in a layer of surface hoar buried on Feb-27. On Sunday, there was a fatal avalanche near Sicamous that occurred on a north aspect at 2025 m that most likely ran on the Feb-27 surface hoar layer.

Snowpack Summary

A surface crust that formed on all aspects up to at least 1700 m is expected to get buried by new snow. In the Monashees, you may find an additional thin crust (from Mar-5) in the top 40 cm of snow that was reactive up to size 2 on Sunday. Approximately 70 cm below the surface lies a variable interface that comprises surface hoar, facets, a crust, or some combination of all three. This layer was buried on or around Feb-27 and has been very active since the weekend. I anticipate this layer will continue to be reactive to sled or skier traffic and/or additional loading from new snow. A previous surface hoar/crust layer buried Feb-10 is now down over a metre. This layer has become less likely to trigger, but continues to be discussed as a possible failure plane by commercial operations. It's presence keeps open the possibility of very large avalanches, as a small surface slide could step down into this deeper layer.

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