Bulletin d’avalanche

Purcells

Mar 21 – 22, 2022Avalanche Canada
Voir sur la carte
Archivé · expiré 5 years ago

Danger d’avalanche

Wed
Thu
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
Ouvrir la carte complète

Points saillants

Avalanche danger will increase as temperatures rise throughout the day. There is uncertainty around how the snowpack will handle this warm-up. 

Choose increasingly conservative terrain as temperatures rise.

Problèmes avalancheux

  • Wind Slabs

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

    Recent snowfall and westerly winds are expected to have formed wind slabs in lee features in the alpine and treeline.

  • Cornices

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3.5

    Cornices have grown significantly in the past two weeks. Warm temperatures may make cause cornices to become weak. Cornice failures are dangerous on their own, but also have the potential to trigger larger avalanches on the slopes below.

    Give them a wide berth when travelling on ridge-lines and minimize overhead exposure to large cornices.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–3

    This is mainly a concern in the western part of the region that received greater snowfall amounts last week. 30 to 70 cm of settled storm snow has shown evidence of forming a persistent slab above weak layers. The most reactivity has been observed on south-facing aspects, with reports of a poor bond to underlying sun crust layers. Weak surface hoar crystals may also exist in isolated areas on north-facing slopes.

Confidence

Moderate - Uncertainty is due to the fact that cornice falls are particularly difficult to forecast. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

MONDAY NIGHT: Cloudy with isolated flurries. Light westerly winds. Freezing level around 1000 m.

TUESDAY: Partially cloudy. Light to moderate westerly winds. Freezing level rising to 2000 m.

WEDNESDAY: Mainly cloudy, light flurries. Moderate to strong westerly winds. Freezing level around 2000 m.

THURSDAY: Mainly clear. Light northwesterly winds. Freezing level around 1000 m.

Avalanche Summary

Several natural and one human-triggered wind slabs occurred in the northwest of the region on Sunday in the alpine and treeline (size 1-2.5).

We have heightened concern about a developing persistent slab problem in some parts of the Purcells (read more in this blog).

Several notable human-triggered slab avalanches occurred last week, suggesting that the recent snow is bonding poorly to the underlying layers. These occurred on a range of aspects above 2000 m, with the most notable reactivity observed on south-facing aspects. Most slabs were small in the top 20 to 30 cm of snow (size 1), but one larger 70 cm thick slab was remotely triggered from below by a group of skiers (size 2). This avalanche occurred on a south aspect at 2250 m.

Snowpack Summary

10-20 cm of recent snowfall overlies last week's 30-70 cm of settled storm snow. Snow depths taper significantly with elevation, with moist and crusty surfaces below 1800 m and on south aspects into the alpine.

In some areas, last week's snow is well bonded to old crust layers, while in other areas the snow has settled into a reactive slab above weak layers around the crusts. At this point, it appears persistent slab problems could be developing in the deeper snowpack areas along the western side of the range. The lower snowpack is generally well bonded.

Terrain and Travel

  • The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
  • Use ridges or ribs to avoid areas of wind loaded snow.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Cornice failure may trigger large avalanches.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

Régions couvertes