Bulletin d’avalanche

Purcells

Mar 20 – 21, 2016Avalanche Canada
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Archivé · expiré 11 years ago

Danger d’avalanche

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

Watch for fresh storm slab formation at upper elevations and continue to seek out conservative terrain in an effort to avoid tangling with the deeply buried persistent weak layers.

Problèmes avalancheux

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    3–5
    Large unstable cornices overhang countless ridge lines and many of these cornices are teetering on the brink of failure.  The weight of an approaching rider, a bit of wind or a period of sunshine could easily induce natural collapse.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3–6
    There are a few different persistent weak layers in the snowpack that are capable of producing large destructive avalanches.  While these interfaces are likely getting harder to trigger, they remain problematic.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1–2
    Sunday night's storm should produce 1 to 5 cm of new snow accompanied by moderate to strong southwest winds.  Watch for fresh slab formation in wind exposed features at and above treeline.

Confidence

Moderate

Weather Forecast

A weak upper low moves into the region Monday displacing the ridge that was in place over the weekend. With the ridge collapsed, the door is open to a series of fast moving storms interspersed by the odd ridge. SUNDAY NIGHT: Freezing level around 2000 m, 1 to 5 cm of snow above 2000 m, rain below, moderate SW wind. MONDAY: Freezing level around 1700 m, 1 to 3 cm of snow at and above treeline, light to moderate southwest wind. TUESDAY: Freezing level starting near valley bottom rising to about 1700 m, light northwest winds, no significant precipitation. WEDNESDAY: Freezing level starting near valley bottom rising to about 1600 m, trace of snow possible, light southwest wind.

Avalanche Summary

On Saturday several natural and explosive initiated cornice failures to size 2.5 were reported. In the north of the region on friday control work produced several size 2 to 3 persistent slab avalanches on high elevation north through east facing features. These avalanches were failing on the mid and early February persistent weak layers.

Snowpack Summary

At ridgetop, cornices are huge and remain weak. Old wind slabs still linger on lee features at treeline and in the alpine which may become more reactive with solar radiation. 40-90cm below the surface you'll find a persistent weak layer comprised of surface hoar, facets and/or a thick crust. This layer seems variably reactive. In other words, it's still reactive to human triggers in some places while in other spots it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. I'd continue to be suspicious of steep, unsupported features at treeline and in the alpine as this layer has the potential to produce large avalanches. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but still has the potential to produce very large avalanches in isolated locations with a heavy trigger or significant warming.

Régions couvertes