Bulletin d’avalanche

Purcells

Feb 26 – 27, 2023Avalanche Canada
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Archivé · expiré 4 years ago

Danger d’avalanche

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

Light snowfall will overly a wind affected snowpack, disguising recent wind slabs and building fresh ones. Take care around ridgelines and wind loaded features on all aspects.

The lower snowpack remains weak, small avalanches may easily step down to deeper layers. Keep a large margin of error by avoiding thin start zones and large slopes.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1–2.5

    Expect variable wind affected surfaces on all aspects and at all elevations. Strong north/east winds from earlier this week have now been replaced by southwest winds building fresh wind slabs.

    Watch for wind loading mid to low on slopes, and be wary of cross-loaded features. Wind affected snow may sit over a layer of surface hoar in sheltered terrain features, or over a sun crust on south facing slopes which may increase reactivity.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–4

    The base of the snowpack remains very weak. Very large human triggered avalanches are possible at higher elevations. Avoid shallow and rocky areas, where the snowpack varies rapidly from thick to thin.

    The mid and lower snowpack also contain several surface hoar layers. Due to the overall weak snowpack structure, small avalanches are likely to step down to any of the deeper weak layers creating large and destructive avalanches.

Confidence

Moderate

Avalanche Summary

Explosive control over the last 4 days has produced slab avalanches to size 3, including one deep persistent slab avalanche. Evidence of a natural cycle to size 3 continues to be observed. With the variable strong winds, activity was observed on all aspects and elevations.

Deep persistent slab avalanches continue to be periodically reported throughout the region. Including a very large skier-triggered, fatal avalanche last Thursday. This MIN post from Thursday observed a size 3 avalanche near Golden over 1 m deep. Likely a naturally triggered slab, the exact failure plane is unknown. The continued activity indicates the weak and unpredictable snowpack remains concerning.

Snowpack Summary

Low density storm snow will sit over recent snowfall, redistributed by wind into wind slabs on all aspects.

A layer of surface hoar is now buried by 30 to 50 cm in sheltered terrain and a thin sun crust on steep south-facing terrain. In general, the mid snowpack is well consolidated and bonding.

The lower snowpack contains a number of buried weak layers such as surface hoar with variable distribution, as well as a widespread layer of large, weak basal facets and depth hoar in places. These weaknesses have been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.

Weather Summary

Saturday Night

5 cm overnight, favoring the north. Freezing levels remain below valley bottom with alpine highs of -15 °C. Moderate southwest winds continue.

Sunday

Snow continuing over Sunday, 5 cm throughout the day. Freezing levels around 500 m. Alpine high of -7 °C with moderate southwest winds.

Monday

Cloudy with moderate southerly winds easing slightly. Alpine high of -9 °C. Freezing levels below valley bottom. Possible flurries.

Tuesday

A mix of sun and cloud with light southerly winds. Freezing levels below valley bottom, alpine high of -9 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Keep your guard up at lower elevations. Wind slab formation has been extensive.
  • Avoid rock outcroppings, convexities, and anywhere the snowpack is thin and/or variable.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Régions couvertes