Bulletin d’avalanche

South Coast Inland

Dec 30 – 31, 2019Avalanche Canada
Voir sur la carte
Archivé · expiré 7 years ago

Danger d’avalanche

Wed
Thu
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
Ouvrir la carte complète

Points saillants

Although the likelihood of triggering avalanches is decreasing, a persistent slab problem remains a concern in the northern part of the region. Danger in the south of the region is LOW.

Problèmes avalancheux

  • Wind Slabs

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

    At upper elevations, southwest winds previously drifted the most recent 5-15 cm of snow into wind slabs that may still be reactive to human triggering. Expect this problem to be most pronounced in the immediate lee of wind-exposed terrain features. Wind slab releases currently carry a serious risk of triggering a deeper weak layer, especially in shallow, rocky areas in the northern part of the region.

  • Persistent Slabs

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

    A problematic weak layer is buried 30-70 cm deep in the snowpack in the north of the region. This layer has produced large and destructive avalanches that have travelled far. The likelihood of triggering is decreasing, but the fundamentally unstable snowpack structure remains a serious concern in the north of the region.This problem is largely absent in the south of the region.

Confidence

Moderate - Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Sunday night: Mostly cloudy, isolated flurries with a trace of accumulation, light southwest winds, alpine temperatures -5 C and freezing levels near 1000 m.

Monday: Cloudy with isolated flurries with 1-3 cm of accumulation, moderate southwest winds, alpine high temperatures around -3 C, with freezing levels around 800 m.

Tuesday: Cloudy, 5-10 cm of snow, moderate to strong southwest winds, alpine high temperatures around -1 C, with freezing levels around 1000 m.

Wednesday: Cloudy, 5-10 cm of snow, moderate to strong southwest winds, alpine high temperatures near 0 C with freezing levels rising to 1500 m.

Avalanche Summary

Avalanche activity has decreased since the widespread avalanche cycle a week ago, and no recent activity has been reported. During that cycle, avalanches were reported to be running to valley-bottom in the north of the region, failing on deeply buried weak layers. See this MIN report of an avalanche involvement from last week for an example of this avalanche problem.

The possibility for large human-triggered persistent slab avalanches remains a concern at higher elevations in the northern part of the region (e.g., Duffey, Hurley, etc.), especially as recently formed wind slabs create the potential for small avalanches to step-down to these layers. These persistent weak layers continue to produce concerning snowpack test results and are expected to heal slowly. 

Snowpack Summary

Snowpack variability between the northern and southern parts of the region is significant. 

In the north (e.g. Duffey, Hurley) 5-15 cm of recent snow has been drifted into shallow, reactive wind slabs on leeward features at upper elevations. Below the surface, a weak layer from late November (down 30-70 cm), composed of sugary faceted grains and hard melt-freeze crust, is a recipe for large and destructive avalanches. It presents a persistent slab problem that may persist for weeks to months. This persistent weak layer is largely absent in the south of the region.

Terrain and Travel

  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Régions couvertes