Bulletin d’avalanche

South Rockies

Jan 20 – 21, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Fri
Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

Look for pockets of loose snow in sheltered terrain. Dig down and investigate deeper layers before committing to big features.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Winds will impact any loose snow available. Hard wind slabs may be stubborn, however slabs will be dense and firm when triggered.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    Avalanches on this layer are unlikely, however they will be large and destructive if they do happen. In some areas the concern is weak snow around crusts 60 to 120 cm deep, while in others it's weak snow near the bottom of the snowpack. Human triggering of these layers are most likely in steep, rocky slopes with a shallow or thin to thick snowpack.

Weather Forecast

TUESDAY NIGHT- Cloudy / Strong southwest wind, 30-60 km/h / Alpine low temperature near -10

WEDNESDAY - Cloudy with sunny breaks / Southwest wind, 20-40 km/h / Alpine high temperature near -8

THURSDAY - Sunny with clouds / Northeast wind, 10-20 km/h / Alpine high temperature near -10

FRIDAY - Sunny / Northeast wind, 10-25km/h / alpine high temperature near -9

Confidence

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

Avalanche Summary

Last Thursday (Jan 14), explosives triggered a size 2.5 wind slab avalanche, and one natural size 3 persistent slab avalanche, both occurred on southeast aspects in the alpine. Additionally, a natural size 3 persistent slab avalanche was reported on a large south-facing alpine slope in the Crowsnest Pass area and a size 3 persistent slab avalanche was reported on an east aspect at 2400 m in the neighboring Waterton National Park region.

The day prior (Wednesday, Jan 13), several natural avalanches to size 2.5 were observed and explosives also triggered avalanches up to size 2.5.

Avalanche activity has dropped, however these recent avalanches are a prime example of the "low probability; high consequence" scenario that persistent slab problems often create. 

Snowpack Summary

A variety of wind affected surfaces covers upper tree line and alpine terrain. A polished crust is found up to 1800 m and higher on solar slopes.

Soft pockets of redistributed snow may hide in sheltered areas.

The lower snowpack consists of decomposing crusts and weak, faceted snow. In the Elk Valley, a decomposing surface hoar layer can be found around one of these crusts 60-120 cm below the surface. Avalanche activity on these layers in the lower snowpack has been sporadic, mostly triggered by large loads such as a wind slab avalanche, or a cornice fall. These deeper weak layers are most likely to be human triggered on steep, rocky slopes with a shallow or thin to thick snowpack.

Terrain and Travel

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Régions couvertes