Bulletin d’avalanche

Sea To Sky

Mar 9 – 10, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Sun
Mon
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Avalanche conditions are very dangerous at this time.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    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
    Possible - Likely
    Taille
    4–8
    Heavy loading is expected reinvigorate this 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
    Possible - Likely
    Taille
    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

Good

Weather Forecast

Friday night: 5-10 cm new snow expected to fall, with freezing levels around 1000 m and SW winds gusting 60-80 km/h. Saturday: Light precipitation, ramping up in the afternoon, with 10-15 cm new snow anticipated by the end of the day. Moderate southwest winds are expected with freezing levels around 1000 m. Sunday: An additional 15-25 cm new snow is expected by the end of the day. Winds strong southwesterly. Freezing levels staying around 1000m. Monday: Another, more intense storm system arrives, bringing 40-50 cm new snow, temperatures cool enough for snow at most elevations and high winds.

Avalanche Summary

There have been at least two close calls involving snowbobile-triggered avalanches in the region over the last couple of days, one of which was triggered from 200m away from below. A size 2 natural avalanche was reported from Garibaldi Park at 1800m on a N aspect on Friday. There was 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. W. 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

New snow accompanied with strong southwest winds are setting up new storm slabs and wind slabs overlying a variable previous snow surface comprising crusts, moist snow and old wind slabs. Previous storm snow amounts were in the region of 50+ cm and this snow bonded poorly to the older surfaces below. The instabilities associated with both these storm slabs as well as deeper weak layers buried within the snowpack have given us a situation where avalanches could initiate in the upper storm snow and easily propagate to lower weaknesses in the snowpack. This dramatically increases the potential size of avalanche occurrences, which is pushing up into the size 3-4 category. There is also the possibility for avalanches to be remote-triggered, triggered mid-slope, and/or propagate into low-angled terrain.

Régions couvertes