Bulletin d’avalanche

South Coast Inland

Mar 6 – 7, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

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

Slabs formed from Thursday's snow may take some time to bond, particularly in wind-loaded terrain features. Intense sun could destabilize sun-exposed slopes and cornices will weaken.

Problèmes avalancheux

  • Wind Slabs

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

    Around 15 to 25 cm of snow fell across the region on Thursday with strong south to southwest wind. Wind slabs likely formed rapidly during the storm and they may remain touchy to human traffic on Friday. Sun-exposed slopes should be treated as suspect during periods of intense sun. Cornices have also likely grown large and could fail during sunny conditions or from the weight of a human.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    1.5–2.5

    A weak layer of feathery surface hoar may be found around 40 to 80 cm deep on northerly aspects around treeline and lower alpine elevations. This layer may be spotty and only found in sheltered terrain features. Assess the layer in the snowpack prior to committing to avalanche terrain or adopt a conservative mindset to avoid the problem.

    In the north of the region (e.g. Duffey, Hurley, Goldbridge), a persistent weak layer of faceted grains near the ground presents a lingering concern on steep, shallow slopes in the alpine.

Confidence

High - Confidence is due to a stable weather pattern with little change expected.

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall, accumulation 10 to 15 cm in the south of the region and 2 to 5 cm in the north, moderate southwest wind, alpine temperature -10 C.

FRIDAY: Mix of sun and cloud, light southwest wind, alpine temperature -10 C, freezing level 1000 m.

SATURDAY: Mix of sun and cloud with isolated flurries, light southwest wind, alpine temperature -10 C, freezing level 800 m.

SUNDAY: Early-morning snowfall then mix of sun and cloud, accumulation 2 to 5 cm, light west wind, alpine temperature -10 C, freezing level 900 m.

Avalanche Summary

A few small (size 1) wind slabs were triggered in the region on Wednesday. They released naturally and by humans. 

Although we do not have reports yet of avalanche activity from Thursday, it is suspected that many storm and wind slab avalanches were triggered naturally and by humans within the new storm snow. Natural avalanche activity should decrease on Friday, with the exception of sun-exposed slopes during intense sunny conditions. Human-triggering of avalanches may remain likely on Friday.

Snowpack Summary

Thursday's storm dropped around 15 to 25 cm of snow across the region. The snow fell with strong south to southwest wind, forming wind slabs in lee terrain features at treeline and alpine elevations.

A weak layer of surface hoar crystals and/or faceted grains may be found around 40 to 80 cm deep on northerly aspects at treeline and lower alpine elevations. The layer may have been destroyed by strong wind immediately before burial on February 22nd, but it may still exist in sheltered terrain features. Where it exists, it has been reactive in some snowpack tests but not others, suggesting spatial variation. This persistent weak layer warrants investigation and a conservative terrain use strategy. Check out the latest forecaster blog that offers a deeper dive into these conditions.

In the northern part of the region (i.e., Duffey/Hurley/Goldbridge), a deep instability exists at the base of the snowpack. It has not produced an avalanche since February 17th. Human-triggering is unlikely, though if one were to trigger the layer, it would likely be in a thin, shallow, rocky spot. A large load, such as from a cornice fall, or rapidly changing weather have the potential to trigger this layer.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Régions couvertes