Bulletin d’avalanche

South Columbia

Mar 3 – 4, 2013Avalanche Canada
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Archivé · expiré 14 years ago

Danger d’avalanche

Tue
Wed
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Problèmes avalancheux

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–4
    The storm has left many large cornices in it's wake on lee slopes, many of which are teetering on the brink of failure.  Cornice fall has the potential to initiate large destructive avalanches.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    3–7
    A weak layer of surface hoar and/or a crust is now down 100 cm or more. This weakness has been susceptible to remote triggering and has been reported from all elevations and aspects.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–7
    We may see another round of natural avalanche activity when slopes start receiving direct sun.  Human triggering remains a concern as the snowpack adjusts to it's new load and storm slab avalanches may step down to the buried surface hoar.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Synopsis:  The pineapple express is being replaced with a ridge of high pressure that should remain in place through Monday.  A weak frontal wave makes it’s way inland Tuesday, but confidence in the exact timing and intensity are poor on Tuesday. Monday: Freezing level at 1000m.  No precip.  Increasing cloud cover.  Light South wind.Tuesday: Freezing level remaining near 1000m.  Light SW wind.  Isolated flurries with no significant accumulation.  Wednesday: Freezing level once again at 1000m.  Light SW wind.  Isolated flurries with no significant accumulation.

Avalanche Summary

Our office continues to learn about the wild widespread avalanche cycle that occurred on March 1st.  Avalanche size during the storm averaged size 3 but the occasional size 4 has been reported too.  I suspect more details will trickle in as visibility improves.

Snowpack Summary

The moisture laden storm has brought the two week total up to 120 - 150cm.  The recent storm was very warm and as a result rain fell as high as 1900m.  I suspect a crust now rests on the surface below 1900m as temperatures have dropped back down below freezing.Below the storm snow lies a highly reactive weak layer of surface hoar (and/or a crust) which was buried on February 12th. Strong southwest winds have redistributed the new snow into deep wind slabs on exposed lee slopes and cross-loaded gully features. The February 12 layer is primed for triggering and has been reacting readily to both natural and human triggers on all aspects and a wide range of elevations. Deeper persistent weak layers from early February and late January continue to show planar failures when moderate to hard forces are applied in snow pack tests. In particular, in the Monashees, a rain crust buried down 150 cm has been responsible for a couple of recent large, surprising avalanches. Immediately following the current storm, the presence of this deeper weak layer could further increase the potential size of avalanche events.

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