Bulletin d’avalanche

Kootenay Boundary

Feb 4 – 5, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Sat
Sun
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

A weak layer of surface hoar has produced very large avalanches in recent days at treeline and below treeline. Stick to low angle terrain and exercise a high degree of caution around open glades.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    50-80 cm of snow sits on a persistent weak layer that was buried near the end of January. This layer consists of a melt-freeze crust in some areas, surface hoar in sheltered areas, and facets in some areas. This layer has been the most reactive at treeline and below treeline, where it exists as surface hoar.

    Another layer of surface hoar that was buried in mid-January may still be possible to trigger, and it is now down about 80-100 cm.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Storm slabs may continue to be reactive, especially in wind loaded areas at higher elevations.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy / moderate northwest wind / alpine low temperature near -11 

THURSDAY - Cloudy with sunny periods and isolated flurries / moderate to strong northwest wind / alpine high temperature near -10

FRIDAY - Cloudy with sunny periods and isolated flurries / moderate to strong northwest wind / alpine high temperature near -6 / freezing level 1500 m 

SATURDAY - Mainly cloudy with a few flurries / moderate west wind / alpine high temperature near -9

Avalanche Summary

There were numerous natural, human and explosives triggered avalanches reported on Tuesday, up to size 3.5. Most of these avalanches failed on the recently buried persistent weak layer. It is notable, however, that a size 3.5 was reported to have failed on a crust that was buried in early December. A smaller avalanche stepped down to this deeper layer, resulting in a very large and destructive avalanche.

There have been numerous reports of natural, human, and explosives triggered avalanches up to size 2.5 reported in the region since last Thursday. The majority of these avalanches failed on the recently buried persistent weak layer. Specifically, these avalanches mainly occurred in areas around treeline, where that layer exists as surface hoar.

Snowpack Summary

20-40 cm of snow sits on a freezing rain crust in some parts of the region. It is not known how widespread this layer is, but it may have the potential to produce avalanches where it exists.

There is now about 50-80 cm of recent storm snow sitting above a persistent weak layer that consists of facets in some areas, a melt-freeze crust in many areas, on a sun crust on steep south-facing slopes, and large surface hoar in sheltered areas. This layer has been the most reactive at treeline and below treeline, where it exists as surface hoar.

There are potentially several more layers of surface hoar in the upper snowpack, with the most notable one down about 80-120 cm. This layer was buried in early January. 

A crust surrounded by weak faceted grains is buried deep within the snowpack. It may be possible to trigger this layers with a large load.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Avoid freshly wind loaded terrain features.

Régions couvertes