Bulletin d’avalanche

Sea To Sky

Dec 1 – 2, 2011Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Sat
Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Points saillants

New snow and sunshine will make the mountains very inviting over the next few days; however, the complex snowpack and potential for triggering large avalanches requires some patience and conservative terrain choices.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–4
    Gusty N-NW winds have formed stiff or hard wind slabs on south through east facing terrain (reverse loading pattern). Old buried wind slabs are still lurking on exposed northerly aspects.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    3–6
    Be particularly cautious in shallow or variable snowpack areas and on slopes that did not recently release. I'm thinking rocky alpine start zones and slopes that vary from thick pillows of snow to thin wind scoured areas in a short distance.

Confidence

Fair - Due to limited field observations

Weather Forecast

A weak cold front should cross the region overnight on Thursday bringing gusty NW winds and a chance of light precipitation. The freezing level should drop to around 300m. The ridge of high pressure rebounds on Friday bringing dry and mainly sunny conditions to the South Coast for the next few days. We could see a temperature inversion develop by the weekend with highs of 5 or 6 degrees between 1500 and 2500m on Saturday, and 1500 and 3000m on Sunday.

Avalanche Summary

There is a report of a Size 2 skier triggered avalanche near Whistler on Tuesday that resulted in minor injuries. Recent explosive control work produced mainly Size 1-2 slab avalanches or no results. This shows that avalanches may be harder to trigger, but the potential for isolated very large avalanches still exists. Careful terrain selection is the key this weekend.

Snowpack Summary

We are dealing with a complex and somewhat unusual snowpack for the South Coast. Around Whistler there are several different persistent weak layer deep in the snowpack including a layer of depth hoar right near the base of the snowpack and at least two distinct crust/facet combinations between 50-100cm above the ground. Recent storms have dumped up to 200cm of snow on top of the weak underlying snowpack. This new load resulted in many large avalanches during the storm and several large to very large human or explosive triggered avalanches shortly after the storm. Keep in mind that rain followed by cooler temperatures have helped to stabilize the snowpack at and below treeline. The greatest concern is with slopes above 1900m that have not recently avalanched. This is not the classic coastal instability where you can charge hard a few days after the storm. Be patient and realize that a large avalanche may become more difficult to trigger over time, but the consequences of a deep release could be devastating.

Régions couvertes