Bulletin d’avalanche

South Columbia

Apr 5 – 6, 2017Avalanche Canada
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Archivé · expiré 9 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

Cornice falls have been responsible for most of the avalanches reported in the past few days. Storm slabs or cornices may trigger persistent weak layers resulting in large avalanches.

Problèmes avalancheux

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3
    Cornices are large and may fall off naturally due to loading from new snow, wind, or daytime warming. Cornice falls in motion may release persistent weak layers resulting in large avalanches.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–4
    A cornice fall or smaller slab avalanche could trigger large, destructive avalanches on deeply buried weak layers. The likelihood of this happening will increase as solar warming weakens unstable cornices and storm slabs over the course of the day.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–3
    New storm slabs are expected to develop due to forecast new snow and wind. These storm slabs may be very touchy where they are sitting on a recently buried layer of surface hoar. This is more likely on shaded slopes in the alpine.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

Overnight: 5-8 cm of new snow with moderate-strong southwest winds and freezing down to 1500 metres. Thursday: 10-15 cm of new snow above 1500 metres with strong southwest winds, and daytime freezing up to 1800 metres. Friday: Freezing down to 1000 metres before a mix of sun and cloud brings the freezing level back up to 2000 metres with light winds. Saturday: Overcast with 5-8 cm of new snow and light winds. A cooling trend should start to drop the daytime freezing levels.

Avalanche Summary

Several natural cornice falls up to size 3.5 were reported on Tuesday in the Monashees and the Selkikrks. Natural cornice and one persistent slab avalanche up to size 3.5 were reported from the Monashees on Monday. The persistent slab avalanche was triggered by a wind slab in steep terrain on a southwest aspect at 2400 metres. On Sunday natural cornice falls released up to size 2.5, and one pulled an unsupported slope resulting in a deep slab release. There were also several reports of skier controlled and accidentally triggered storm slabs up to size 1.0.

Snowpack Summary

New snow is forecast to develop new storm slabs in the alpine and at treeline. These new storm slabs are developing above a mix of old surfaces that include melt-freeze crusts on solar aspects in the alpine, and all aspects at treeline. In some areas the new snow may hide some lingering wind slabs that are left from the last stormy period. The biggest problem lately has been large and fragile cornices that have regularly fallen off naturally with loading from wind, or due to warming from direct sun or daytime heating. The February weak layers are down about 160-200 cm and the deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack. These deep weak layers have been released with large triggers like cornice falls, and they may be more likely to fail on southerly aspects during periods of strong solar radiation or from heavy loading from storm snow. Expect cornices to experience new fragile growth during the next few stormy days.

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