Avalanche forecast

Sea To Sky

Mar 7 – 9, 2012Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–4
    Recent variable winds have deposited fresh wind slabs in unusual places, but generally lurking below ridgecrests, behind terrain features and in gullies. Cornices are expected to weaken with warm temperatures and could trigger large wind slabs below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    Warming temperatures combined with the potential for cornice triggers, remote triggering, step down avalanches, and wide propagations makes this persistent slab problem particularly tricky to manage.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–6
    Touchy weaknesses within and under the recent storm snow are expected to become more reactive with sun-exposure. Cohesionless low-density snow overlying a crust can produce very large loose-snow avalanches.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Thursday: Increasing clouds throughout the day and moderate snowfall starting in the evening. Light winds increasing to strong southeasterlies with the onset of the storm. Freezing levels rising as high as 2000m, or higher in southern areas, but dropping in the evening. Friday: Heavy snow and strong southwesterly winds tapering off in the morning with 30-40cm total possible by the end of the day. Freezing levels are expected to drop to 700m. Saturday: Continued moderate precipitation and strong winds with freezing levels remaining in the 500-700m range.

Avalanche Summary

We received an initial report of an avalanche fatality in the southern Pemberton Icecap area on Tuesday. So far we know that a single snowmobiler was buried and perished in a Size 3 avalanche. The avalanche occurred on an east aspect at approximately 1700m, the slab was estimated to be 1.5-2.0m thick and 400m wide and suspected to have stepped-down to the mid-February persistent weakness. We will provide more details as they come available.

Snowpack Summary

Strong and variable winds in exposed treeline and alpine areas has resulted in reverse loading, sastrugi, surface crusts, and looming undermined cornices. Dribs and drabs of new snow over the past couple of days adds to the approximately 50cm of recent low density storm snow. Loose surface snow, storm slabs, and/or weak wind slabs are bonding poorly to a variety of old snow surfaces, including crusts, faceted snow, and wind slabs, from last week. Recent winds and precipitation patterns have created a highly variable somewhat upside-down upper snowpack. Storm and wind slabs have shown propensity to propagate in low angled terrain and step-down to deeper weaknesses.

Regions covered