Bulletin d’avalanche

South Rockies

Feb 2 – 3, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Thu
Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

New snow accompanied by a strong southwest wind will build touchy wind slabs in leeward terrain features. The new snow may have a poor bond to the old snow surfaces, especially where it sits above a buried surface hoar/ crust/ facet interface. 

Problèmes avalancheux

  • Wind Slabs

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

    Moderate to strong southwest wind will continue to redistribute the new snow and build wind slabs in lee terrain features in the alpine and at exposed treeline. These slabs will be particularly reactive where they overlie surface hoar. It is uncertain how well the transported snow will bond with other old surfaces, for example, hard wind affected layers. 

    Cornices might grow larger and become more fragile.

Confidence

Low - Forecast snowfall amounts are uncertain.

Weather Forecast

Monday Night: Snow amounts 5-10 cm with 50-80 km/hr ridgetop wind from the South. Alpine temperatures near -1 and freezing levels 1300 m.

Tuesday: Snow 5-15 cm. Strong and gusty southwest wind. Alpine temperatures near -1 and freezing levels 1400 m.

Wednesday: A mix of sun and cloud with isolated flurries. Alpine temperatures -6 and freezing levels at the valley bottom. Ridgetop wind 45 km/hr from the West.

Avalanche Summary

On Sunday, reports of size 1-1.5 wind slabs were triggered by explosives. No natural avalanches were reported.

Several loose dry avalanches up to size 2 were reported in steep alpine and treeline terrain on the weekend. 

With the forecast snow and strong wind, the persistent slab may reach the threshold and become reactive, especially to skier and rider triggers.

Snowpack Summary

20-30 cm of recent snow buried surface hoar and old surfaces. On steep solar aspects a sun crust can be found underneath the new snow. In the alpine and upper treeline, the new snow sits on top of layers of hard wind slab, scoured areas, sastrugi and isolated pockets of soft snow. A hard thick crust is found up to 1900 m. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack (100-150 cm deep). Avalanche activity on these layers has been sporadic and mostly triggered by large loads such as wind slab avalanches and cornice falls. Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be carefully assessed and approached with caution.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid terrain traps where the consequence of any avalanche could be serious.

Régions couvertes