Bulletin d’avalanche

Sea To Sky

Mar 8 – 9, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Sat
Sun
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–5
    Recent variable winds have deposited fresh wind slabs in unusual places, but generally lurking below ridgecrests, behind terrain features and in gullies. Heavy loading is expected to cause large natural avalanches.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    3–8
    Heavy loading is expected reinvigorate the mid-February persistent weakness. The potential for remote triggering, step down avalanches, and wide propagations makes this persistent slab problem particularly tricky to manage.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–5
    Any new snow is expected to initially bond poorly, and deeper weaknesses within and under recent storm snow are expected to be overloaded.

Confidence

Fair - Intensity of incoming weather is uncertain for the entire period

Weather Forecast

Friday: Heavy snow and strong southwesterly winds. 30-40cm possible by the end of the day for immediate coastal areas, but expected to be dryer inland. Freezing levels are expected to drop to 1000m. Saturday and Sunday: Continued moderate snowfall and strong south to southwest winds with freezing levels remaining in the 500-1000m range.

Avalanche Summary

We received an initial report of an avalanche fatality in the Brandywine 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. More reports of last weekend's widespread large natural avalanche cycle are coming in with observations of Size 4.5 avalanches. Some of the larger slabs propagated 2-3Km along ridgelines and stepped down to the mid-February persistent weakness, and there's no reason why similar avalanches can't happen with this next round of loading.

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 release mid-slope, propagate into low angled terrain, and step-down to deeper weaknesses.

Régions couvertes