Bulletin d’avalanche

Northwest Coastal

Apr 6 – 7, 2014Avalanche Canada
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Archivé · expiré 12 years ago

Danger d’avalanche

Tue
Wed
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Points saillants

Monday's storm will pack a punch and is driving the Danger Ratings. The snowpack does not typically handle rapid change well and deeply buried persistent weak layers may re-awaken.

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–5
    New snow driven by strong ridge top winds will likely create touchy slabs at and above treeline. This snow adds to existing storm snow and is expected to be unstable initiating large-very large avalanches.

  • Wet Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–4
    At lower elevations the snowpack will likely become saturated and weak with heavy rainfall. Wet slab avalanches typically move slower, however they are very destructive and can mow down anything in their path.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3–7
    Two buried weak layers exist in the snowpack. These weak layers could be activated by cornice fall, a surface avalanche in motion, or intense loading from snow, rain and wind. Avalanches failing on these weak layers will be large and destructive.

Confidence

Good

Weather Forecast

Starting tonight an intense, direct frontal system will slam the North Coast bringing heavy precipitation, rising freezing levels and strong to extreme southerly winds.Sunday night: Freezing levels rising to 800 m and expecting 10-40 cm at higher elevations (higher value indicated for coastal areas). Ridgetop winds generally moderate from the south with strong gusts. Monday: Freezing levels rising to 1700 m and expecting up to 50 mm in coastal areas and up to 30 mm further north (Bear Pass, Stewart, etc.). Ridgetop winds strong from the south gusting to extreme values. Tuesday: Freezing levels falling to 800 m or lower. Precipitation amounts 10-20 mm in coastal areas with lower amounts near 10 mm as you move inland.Wednesday: Snow accumulations 10-20 cm. Ridgetop winds moderate from the west. Freezing levels near 1000 m.

Avalanche Summary

On Saturday, numerous loose wet avalanches occurred below 1200 m. Most operators had limited observations due to poor visibility. The recent storm snow has shown a fairly poor bond to the older snow surfaces. Natural loose dry and wet avalanche activity up to size 2 was reported on Friday. Expect a widespread natural avalanche cycle at all elevations on Monday. It will take a couple of days before things start to settle out. Travel in avalanche terrain is not recommended.

Snowpack Summary

An additional 10-40 cm of snow at upper elevations is forecast, followed by heavy precipitation on Monday. The snowpack will be under the influence of direct rapid change, and will become weak and unstable. This additional load will fall  onto a mix of surface hoar, facets, melt freeze crusts and firm wind pressed snow and will likely have a poor bond. Storm and wind slabs will form, especially at upper elevations. Lower elevations the snowpack will likely become saturated adding to the already isothermal conditions.Two persistent weak interfaces exist deeper in the snowpack. The early March layer can be found down 75 - 100cm and is composed of facets/surface hoar on shady aspects and facets/crust on southerly aspects. The early February crust/facet/surface hoar combo is down 150 - 200cm. This layer was responsible for a couple of unexpected large avalanches right at the end of March and the beginning of April. These layers should be on your radar and could become reactive with intense loading from rain/snow, warm temperatures and strong winds.

Régions couvertes