Bulletin d’avalanche

North Columbia

Jan 14 – 15, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Sat
Sun
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

Ease into terrain very cautiously and tune in to signs of instability like shooting cracks and recent avalanches. Alpine avalanche terrain is best avoided. Be mindful that sunshine can have a powerful effect on stability - and on your desire to push the conditions. 

Problèmes avalancheux

  • Persistent Slabs

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

    A couple of weak layers exist in the mid snowpack, buried 80-150 cm and 120-200 cm below the surface. They are highly variable in distribution and trending toward dormancy, but they are being tested by a new load of new snow. Some potential currently exists for avalanches in surface layers to step down to a deeper layer to create larger, much more destructive avalanches.

  • Storm Slabs

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

    New snow and strong winds have created new slab problems that are likely to vary with elevation and wind exposure. In exposed areas, thick and reactive wind slabs should be expected in leeward features loaded by the wind. In sheltered areas, storm slabs are more likely to exist uniformly across all aspects and be particularly touchy where they overlie surface hoar or crust.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday night: Cloudy with isolated flurries. Light west winds.

Thursday: Mainly sunny. Light variable winds increasing in the evening and becoming strong southwest overnight. Alpine high temperatures around -8.

Friday: Cloudy with scattered flurries bringing 5-10 cm of new snow. Light to moderate southwest winds. Alpine high temperatures around -7.

Saturday: Mainly cloudy. Light south winds. Alpine high temperatures around -7.

Avalanche Summary

We're still awaiting field observations from the aftermath of Tuesday's storm, however it it's safe to assume it was a very busy day for natural avalanches as up to 70 cm of new snow blanketed the region and was redistributed by strong winds. 

A few preliminary observations from the Mica dam area showed numerous natural size 1.5-2 storm slabs on northwest aspects. Only about 30 mm of rain fell in that location (likely translating to about 35 cm at higher elevations. In the Trans-Canada corridor, a size 4 (VERY LARGE) avalanche ran on Mt. Laurie. )

Looking forward, expect Thursday to be another tricky day to be in the mountains, with new and reactive wind slabs formed in wind-exposed areas and even more widespread storm slabs primed for human triggering in more sheltered areas.

Snowpack Summary

An impressive 30-70 cm of new snow fell in the region during Tuesday's storm. The new snow buried wind affected surfaces at upper elevations as well as surface hoar in wind sheltered areas and a thin crust on solar aspects. 

The new snow will take time to form a bond with these previous surfaces, particularly in spots harbouring surface hoar or crust. In exposed areas, elevated winds are almost certainly redistributing new snow into reactive wind slabs and adding to cornices.

A couple of persistent weak layers exist in the upper to mid snowpack:

  • The upper layer, now found an estimated 80-140 cm down, is a spotty layer of surface hoar at treeline and below. 
  • The lower layer, now likely around 110-200 cm deep, is widespread and may present as decomposing surface hoar and/or a crust.

Avalanche activity on these layers has been dwindling since last week and snowpack tests results have generally indicated that they are gaining strength. Given their age (particularly the deeper layer) and the testing load brought by Tuesday's storm, the outlook is good for these layers to finally become dormant as our current surface instabilities diminish.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid exposure to steep sun exposed slopes.

Régions couvertes