Bulletin d’avalanche

Purcells

Jan 20 – 21, 2012Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

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

Danger ratings are based on an expected 40cm of snowfall through Friday and Saturday, coupled with warming and strong winds. However, the weather forecast is uncertain. If less severe weather arrives, danger may be lower than forecast.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–5
    Strong winds will shift available snow into wind slabs on downwind slopes. Older buried wind slabs also exist.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    4–7
    Two layers to watch: 1. Buried surface hoar, most likely triggered on steep, unsupported slopes amongst the trees. 2. Basal facets, triggerable from thin snowpack areas or by a very heavy load (cornice fall, airborne sled). Avalanches could be large.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–5
    A classic recipe for storm slabs is evolving: new snow falling with rising temperatures onto loose dry snow. Storm slab avalanches are likely, especially in steep or convex terrain.

Weather Forecast

Friday night: Moderate snow. Strong south-westerly winds. Alpine temperatures rising to -7C.Saturday: Moderate snow. Strong south-westerly winds. Alpine temperatures rising to -4C in the morning. Sunday: Cloud and flurries. Cooler temperatures. Moderate westerly winds. Monday: Flurries or light snow. Moderate to strong westerlies.

Avalanche Summary

Recent observations include a few cornice failures and isolated skier-triggered wind slabs in the size 1-2 range. Explosives testing released storm slabs, with little in the way of recent deep releases. Avalanche activity slowed down towards the end of the week, but is expected to increase again during the weekend.

Confidence

Fair - Forecast snowfall amounts are uncertain on Saturday

Snowpack Summary

New storm snow is building up over wind slabs in exposed features and over loose dry snow in sheltered areas. Strong winds and warming temperatures forecast to accompany Friday night/Saturday's snowfall are likely to create a more widespread wind slab and storm slab problem. The mid-December surface hoar/facet persistent weakness, now down around 50cm on the eastern side of the range and as deep as 180cm on the western side, is still causing operators concern, especially in shallow snowpack areas. Recent snowpack tests show moderate to hard, sudden planar results on this layer. The consequences of a failure on this layer would be large. Facets and depth hoar exist at the base of the snowpack. Cornices are large and weak in some areas.

Régions couvertes