Bulletin d’avalanche

Purcells

Mar 12 – 13, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

Wed
Thu
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

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Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–7
    Wind slabs can be found below ridge crests, behind terrain breaks, and in gullies. Wind slabs are overloading persistent weak layers and creating large avalanches.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    4–7
    Avalanches have been failing on buried surface hoar, creating surprisingly large avalanches. This problem is tricky to manage, as it could be triggered from afar, on low-angled slopes or by a surface avalanche.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–5
    Storm slabs are building up and are likely to be reactive on steep ground.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Overnight Monday: Heavy snowfall, especially for the southern part of the region. Up to 25-30cm is possible. Strong to extreme south-westerly winds. Freezing level around 1100 m. Tuesday: Heavy snowfall will continue in the morning but become lighter in the afternoon. Winds should also start to diminish. Freezing level should fall slightly. Wednesday: There may be a lull between storms, although snowfall is expected to start up again later in the day.Thursday: Another frontal system arrives in this region, bringing further heavy snowfall, strong south-westerly winds. Freezing level around 1200m.

Avalanche Summary

On Monday, several size 2-2.5 slabs released naturally (likely from wind-loading), which are suspected to have failed on the mid-February persistent weakness. A helicopter remotely triggered a size 1.5 slab, part of which stepped down to basal facets. A skier was also swept over a cliff in a size 1 slab which failed on the mid-Feb layer. On Sunday, a group of skiers triggered a size 3.5 slab 900m wide and 80-140cm deep on a north aspect in the southern Purcells. Late last week, large (size 2.5-3.5) human and explosive-triggered slabs were reported on all aspects, with crowns 40-120cm deep.

Snowpack Summary

Up to half a metre of recent storm snow, driven into wind slabs by moderate to strong southerly winds, overlies moist snow at low elevations or old hard wind slabs in the alpine. The early February surface hoar, about 1-1.6m deep, remains a key concern. Storm slabs, wind slabs or a light load can trigger surprisingly destructive avalanches on this layer. Basal facets have only been reactive on steep, shallow, and rocky slopes, but operators continue to monitor this layer.

Régions couvertes