Bulletin d’avalanche

South Rockies

Mar 10 – 11, 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

Buried weak layers remain possible to be triggered, where they still exist.

Problèmes avalancheux

  • Persistent Slabs

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

    Two persistent weak layers exist in the snowpack:

    • The upper layer is buried 30 to 60 cm and primarily consists of weak faceted grains.
    • The deeper layer is buried 60 to 100 cm and consists of surface hoar, faceted grains, and/or a hard crust. The problem has been most prevalent around treeline elevations and in openings below treeline, but also reaches into the lower alpine. 

    These layers could be triggered by riders anywhere they still exist in the snowpack.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

TUESDAY NIGHT: Clear skies, 20 km/h west wind, alpine temperature -8 C.

WEDNESDAY: Increasing clouds with late-afternoon snowfall, accumulation 2 to 5 cm, 20 km/h west wind, alpine temperature -6 C, freezing level 1500 m.

THURSDAY: Morning clouds then clearing, 20 km/h northwest wind, alpine temperature -5 C.

FRIDAY: Clear skies, 10 km/h northwest wind, alpine temperature -1 C, freezing level rising to 2000 m.

Avalanche Summary

No new avalanches were observed in the past few days. On Saturday, we received a few images of a rider that triggered a persistent slab avalanche near Crowsnest Pass. The avalanche appeared to be large (size 2 or greater) and at below treeline or treeline elevation in a forest burn. It is suspected that the avalanche released on one or potentially both of the weak layers described in the Snowpack Summary, as the maximum slab depth was around 90 cm.

Snowpack Summary

A dusting of snow overlies a thick melt-freeze crust in many areas, with the exception being on north aspects above around 1700 m. Old wind slabs may exist on northerly aspects at alpine and treeline elevations, whereas windward slopes have been scoured to rocks or a hard crust. On solar aspects and below the freezing level, the snow may moisten during the heat of the day.

Around 30 to 60 cm of snow sits above a persistent weak layer of sugary faceted grains that was buried in mid-February. There have been a handful of avalanches that released on this layer in the past few weeks. There is another persistent weak layer that was buried at the end of January, found around 50 to 80 cm deep. This layer consists of feathery surface hoar, facets, and/or a hard melt-freeze crust. Periodic avalanches continue to be triggered on these layers. 

Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack. 

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Régions couvertes