Bulletin d’avalanche

South Columbia

Dec 19 – 20, 2011Avalanche Canada
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Archivé · expiré 15 years ago

Danger d’avalanche

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

New blog post discussing variability in the South Columbias

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–4
    Wind slabs are sliding easily on the recently buried surface hoar. Shifting winds have set up this problem on a variety of aspects, particularly north through south east.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    2–5
    Slab avalanches are now occurring on the mid-Dec surface hoar interface in northern parts of this region (think a band between the TransCanada and a line 50 km to the south). All aspects. Elevation from 1400m to 2300m. Remote triggering possible.

Confidence

Fair - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

Tuesday: 5-10 cm new snow expected with moderate to strong NW ridgetop winds. Alpine temperatures falling rapidly to around -15C by the afternoon. Wednesday: Mostly dry. Light northerly winds. Alpine temperatures around -18C. Thursday: Mostly dry. Winds becoming westerly. Remaining cold, but a mild inversion should elevate alpine temperatures to around -10C.

Avalanche Summary

Both natural and human-triggered avalanches up to size 2.5 were observed on Saturday and Sunday in the Monashees and Selkirks, releasing on the surface hoar layer from mid-December. Notable is the wide distribution, with avalanches reported on all aspects and elevations from 1400 to 2300 m. Most were 30-40 cm deep, although one was reported to have a fracture line up to 70 cm deep. Several remote-triggered avalanches occurred, where the avalanche was triggered by someone riding some distance from where the slide occurred. Sympathetic avalanches were also reported, where one slide initiated other avalanches. With further snowfall, the current pattern of avalanche activity will continue, but the size and destructive force will go up.

Snowpack Summary

A north-south split exists in this region at present as a result of the track of recent storms. Northern and western areas have seen up to 50 cm of recent storm snow, while areas further south have seen more like 20cm. This storm slab is reported to be upside-down, which means higher density snow sits on top of less dense snow. The storm slab sits above a well developed surface hoar layer from mid December, which has been reacting readily to snowpack tests and ski cutting. Additionally, remote-triggered avalanches have been reported on this layer, indicating it has a high potential for fracture propagation. All this info points to the same thing: Where the storm slab is sufficiently thick (in the order of 40 cm) and cohesive, conditions are ripe for slab avalanches. Lower in the snowpack, the mid-layers are well-consolidated and strong. Near the base of the snowpack there are a few layers that have the potential to wake up with a really big storm or very heavy loads (such as a sled airing off a cornice). These include a surface hoar layer from early November, a crust/facet combo from October and the interface on steep glaciated terrain with snow that did not melt over the summer.

Régions couvertes