Bulletin d’avalanche

Kootenay Boundary

Feb 24 – 25, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

Wed
Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

The new snow rests on a weak layer so it may take longer than usual to bond to old surfaces and will likely remain reactive to human traffic. Uncertainty about reactivity of buried weak layers is best managed through conservative terrain choices at this time.

Problèmes avalancheux

  • Persistent Slabs

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

    A layer of weak and feathery surface hoar crystals was buried mid-February and now sits 30-50 cm deep. It has been reactive to human triggering in the past week, typically in open trees in the east of the region. The problem layer may be spottier in the west of the region.

    There is uncertainty around how this layer will react to new snow loads from the present storm. In the long term, more load will help the interface to bond over time. But in the mean time, burying it deeper could make human triggering more difficult but higher consequence as it will produce larger avalanches. Rapid loading could also cause the layer to fail and induce natural activity. Uncertainty about deep weaknesses is best managed through conservative terrain selection.

  • Storm Slabs

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

    10-20 cm of recent snow sits over a weak interface consisting of surface facets, surface hoar or sun crusts (aspect/elevation dependent). Loose dry and small soft slab avalanche activity Sunday has demonstrated that this interface is weak but the overlying snow lacks slab character and propagation propensity. As the storm snow settles into a slab, potential size will increase as reactivity persists. Storm slabs will be deepest where strong winds have loaded lee terrain features in alpine and exposed treeline areas. A forecast switch in wind direction from south to northwest Monday will mean wind loading on a variety of aspects.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Sunday night: Flurries bringing up to 10 cm. Moderate northwest wind. Freezing level 800 m.

Monday: Morning flurries bringing a trace of new snow. Moderate northwest wind. Freezing level 1200 m.

Tuesday: Mix of sun and cloud. Light to moderate northwest wind. Freezing level 1200 m.

Wednesday: Mix of sun and cloud. Light to moderate northwest wind. Freezing level 1500 m.

Avalanche Summary

Reports from Sunday consisted of loose dry sluffs and soft slab avalanches limited to size 1 easily triggered by skier traffic and running on the surface hoar/crust bed surface.

Snowpack Summary

10-20 cm of recent snow is settling into a storm slab over a layer of widespread surface facets, surface hoar in sheltered areas or sun crusts on solar aspects. In the alpine and exposed treeline, recent snow has been redistributed by strong southwest to northwest wind, loading deep deposits into lee features.

An older layer of surface hoar now sits 30-50 cm deep. This weak layer produced significant avalanche activity focesed in the east of the region last week. While it is likely bonding over time, there is uncertainty around remnant reactivity. The remainder of the snowpack is well settled.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.
  • Uncertainty is best managed through conservative terrain choices at this time.

Régions couvertes