Bulletin d’avalanche

Kootenay Boundary

Feb 25 – 26, 2020Avalanche Canada
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Archivé · expiré 7 years ago

Danger d’avalanche

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

Storm slabs are sitting over a weak layer and continue to be reactive. Some uncertainty surrounds a deeper weakness which, if triggered, could produce high consequence avalanches. Uncertainty is best managed by conservative terrain choices and avoiding terrain traps.

Problèmes avalancheux

  • Persistent Slabs

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

    A layer of surface hoar 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 now that it has been buried deeper by the recent 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 triggering more difficult but higher consequence as it will produce larger avalanches. Recent storm avalanche activity has demonstrated that if this persistent layer still has avalanche potential, triggering it requires larger loads than size 1 avalanches. 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

    15-30 cm of recent snow sits over a weak interface consisting of surface facets, surface hoar or sun crusts (aspect/elevation dependent). Touchy but small avalanche activity Sunday and Monday 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 avalanche size may increase as reactivity persists. Storm slabs will be deepest where strong winds have loaded lee terrain features in alpine and exposed treeline areas. Recent winds have varied in direction from south to northwest, wind loading on a variety of aspects.

Confidence

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

Weather Forecast

Monday night: Clear. Light to moderate northwest wind. Freezing level valley bottom.

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

Wednesday: Mix of sun and cloud. Moderate northwest wind. Freezing level 1500 m.

Thursday: Mix of sun and cloud. Light to moderate northwest wind. Freezing level 1800 m.

Avalanche Summary

A natural avalanche cycle occurred Sunday afternoon and overnight, consisting of size 1-1.5 loose dry and soft slab avalanches. Activity was observed on various aspects but was especially concentrated on southeast to southwest where they ran on the surface hoar/crust combo. Slabs were reported to be touchy and easily triggered by skier traffic. Explosive control work conducted Monday produced size 1.5-2 running far on the crust. Reactivity is expected to continue.

Snowpack Summary

15-30 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 focused 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

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Be aware of the potential for human triggerable storm slabs at lower elevations, even on small features.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

Régions couvertes