Bulletin d’avalanche

South Coast Inland

Feb 28 – 29, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

Sun
Mon
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

Incoming snow and increasing wind are expected to complicate the existing wind slab problem. Caution around drifted slopes and roll-overs at upper elevations, especially where these slabs overly a weaker interface.

Problèmes avalancheux

  • Wind Slabs

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

    Southwest winds have drifted the previous 15-40 cm of snow into cohesive slabs onto lee terrain features at upper elevations. These wind slabs overly a variety of interfaces including surface hoar in sheltered areas and a melt freeze crust on steep, sunny slopes. Warming temperatures, 5-10 cm of new snow, and increasing southwest winds on Friday are expected to exacerbate this wind slab problem, especially where it overlies a weaker interface.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2.5–3.5

    In the north of the region (e.g. Duffey, Hurley, Goldbridge), a buried weak layer lingers at the base of the snowpack. This layer has been quiet, with no reports of avalanches on it since mid February. There is potential for it to wake up with rapid warming or significant loading by new snow.

Confidence

Moderate - Uncertainty is due to the timing of the incoming weather system.

Weather Forecast

Thursday night: Cloudy, scattered flurries bringing a trace of new snow, moderate southwest winds, freezing level dropping below 1000 m.

Friday: Mix of sun and cloud, 5-10 cm of snow, moderate southwest winds with strong gusts, freezing level 1600 m in the north, 2000 m in the south.

Saturday: Cloudy, 10-15 cm of snow, winds decreasing and shifting from strong southwest to light northwest, freezing level 1200 m.

Sunday: Mostly clear, light variable winds, freezing level 1200 m. 

Avalanche Summary

Some minor snowballing was reported on steep, sunny slopes Wednesday and Thursday across the region. On Monday and Tuesday, several small to large (size 1.5-2) natural and human-triggered wind slab avalanches were observed on northeast, northwest, and west aspects in the alpine breaking 10-50 cm deep. 

Snowpack Summary

15-40 cm of recent storm snow (closer to 50 cm in the Coquihalla) has been redistributed onto lee features in exposed areas near and above tree line. This snow may overly isolated patches of surface hoar in sheltered areas or sun crusts on solar aspects, and it may remain possible to human trigger. Warming temperatures, 5-10 cm of new snow, and increasing southwest winds on Friday are expected to exacerbate this wind slab problem, especially where it overlies a weaker interface.

In the north part of the region (ie. Duffey/Hurley/Goldbridge), a deep instability exists at the base of the snowpack. It has not produced recent avalanche activity, with the most recent event on February 17. Rapid warming or heavy loading by new snow/wind/rain events has the potential to re-awaken this layer.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.

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