Avalanche forecast

South Coast

Feb 6 – 7, 2016Avalanche Canada
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Avalanche danger

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

The snowpack varies a great deal throughout the region. In the north, you'll likely encounter trickier conditions due to a buried persistent weak layer.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–4
    Cornices are huge and weak. They can be destructive by themselves, and may also become the trigger for a large slab avalanche on the slope below. Use extra caution around ridge crests.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    In the north of the region, persistent weaknesses continue to produce large and destructive avalanches. Conservative terrain selection is still critical.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–4
    Recently formed storm slabs may remain reactive to the weight of a skier in higher elevation lee terrain. At lower elevations where temperatures are expected to rise above freezing, loose wet avalanches are also possible.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Monday

Weather Forecast

On Sunday, expect up to 1-5mm of precipitation which should fall as rain at most elevations. On Monday and Tuesday the region will see increasingly clear skies as a dry ridge of high pressure develops. Freezing levels should rise from 500m to 2600m on Sunday, and then climb to 3600m for Monday and Tuesday. Ridgetop winds should remain moderate from the southwest on Sunday and Monday, and then become light on Tuesday.

Avalanche Summary

Storm slab avalanches to size 2 were observed on Friday in the north of the region in response to new snow and wind. Although observations were limited on Saturday, I'm sure there was evidence of fairly widespread storm slab activity.  Last week, a skier remotely triggered a size 3.0 slab avalanche from 20 metres away that released on the early January surface hoar. This avalanche happened at 2300 metres on a south-southeast aspect in the Duffey Lake area. The fracture propagated 350 metres and ran 750 metres to the valley bottom. Looking ahead, storm slabs may remain reactive to human triggering on Sunday. Also, forecast rising freezing levels and solar radiation should spark a round of loose wet avalanche activity on sun-exposed slopes. Warming will also increase the likelihood of triggering wet slabs and deep and destructive persistent slabs, especially in the north of the region.

Snowpack Summary

On Friday between 25-40cm of new snow fell. Strong southwest winds shifted these accumulations into deep and dense storm slabs. Cornices were already large before the storm, and new growth is expected to be fragile. About 50-80cm below the surface, you likely find a rain crust which formed on January 28th. This crust is widespread and exists up to about 1900m. Previous wet and heavy storms have likely flushed out the deeper mid-January surface hoar in the south of the region; however, this weakness which lies between 60 and 130cm below the surface is still reactive at higher elevations in the Duffey, Hurley and Birkenhead areas. This layer continues to produce sudden results in snowpack tests and has been responsible for recent destructive avalanches. 

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