Bulletin d’avalanche

Northwest Inland

Jan 6, 2017Avalanche Canada
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Archivé · expiré 10 years ago

Danger d’avalanche

Fri
Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

Hard wind slabs over weak facetted snow continue to be a concern for human triggering.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2
    Wind slabs continue to be a concern for human triggering. Recent extreme winds have stripped some exposed north and east aspects and created variable depth deposits on south and west aspects.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3
    The lower snowpack is predominantly weak facetted crystals above a rain crust that developed in November. There are a couple of layers of concern in the mid snowpack, but I suspect that avalanches in motion may step down to the crust or smooth ground

Confidence

Moderate - Due to the number of field observations

Weather Forecast

FRIDAY: Cloudy with scattered flurries bringing around 5 cm of fresh snow, alpine temperature reaching -9 C, and light to moderate easterly ridgetop winds.SATURDAY: Mainly cloudy with scattered flurries bring another 3-5 cm, temperature around -17 C with an alpine temperature inversion, and moderate easterly ridgetop winds.SUNDAY: Sunny with cloudy periods, temperatures reaching -10 C with a strong alpine temperature inversion, and light southeasterly ridgetop winds.

Avalanche Summary

No new avalanches reported. In the north of the region near Ningunsaw there was a natural avalanche size 3.5 that released in the basal facets on Monday. This is a good reminder that large full depth avalanches are possible in shallow snowpack areas. A natural avalanche cycle with slides up to size 2 occurred Friday in the mountains near Smithers. This was in response to the strong northerly winds. Wind slabs will likely remain touchy throughout the forecast period, as sustained winds redistribute any loose surface snow. Deeper persistent weak layers will also remain a concern, it is possible to trigger large avalanches.

Snowpack Summary

Snow depth at treeline varies from about 1 m in most areas to 2 m at deeper snowpack areas in the south and west of the region, and up to 250 cm in the alpine. The shallow snowpack areas mostly consist of weak facetted or sugary grains beneath hard wind slabs. These wind slabs may produce surprisingly long fractures resulting in large avalanches, and in some instances they may step down to weak snow crystals near or at the ground. In addition to the facets, a thick layer of buried surface hoar may be found 20-30 cm below the surface. There is another persistent weakness that formed during the early December cold snap which is now about 40-60 cm deep. A crust from mid-November may be lurking close to the ground nestled in amongst the facets. We don't have a lot of information about these layers, but it's worth noting the weakness responsible for most of the large avalanches during the big storm just before Christmas was the mid-November rain crust.

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