Bulletin d’avalanche

South Columbia

Feb 15 – 16, 2022Avalanche Canada
Voir sur la carte
Archivé · expiré 5 years ago

Danger d’avalanche

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

Points saillants

Manage open slopes at treeline carefully where triggering a persistent slab avalanche is most likely.

Avalanches are unlikely in areas where a hard surface crust is present.

Problèmes avalancheux

  • Persistent Slabs

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

    A weak layer formed by clear skies in late January may be found 40 to 80 cm deep in the snowpack. This layer consists of facetted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain.

    This surface hoar layer has been the culprit of several large human-triggered avalanches in the past week and remains a concern, especially in sheltered areas at treeline. Terrain features to be particularly cautious around include the lee side of ridges, openings in trees, cut blocks, and burns. Where a thick, supportive crust is present on the surface, avalanches on this layer are unlikely. Triggering this layer from a distance away is a concern, watch out for adjacent and overhead slopes. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

A more unsettled weather pattern will bring a mix of sun and cloud and light snowfall throughout the week.

Monday Overnight: Cloudy with light snowfall. Freezing level dropping to valley bottom. Light to moderate northwesterly winds.

Tuesday: A mix of sun and cloud, light flurries. Freezing level rising to 1000 m. Light to moderate northwesterly winds. 

Wednesday: A mix of sun and cloud, light flurries. Freezing level rising to 1000 m. Light to moderate northwesterly winds. 

Thursday: Snowing. Freezing level rising to 1500m. Moderate to strong westerly winds. 

Avalanche Summary

Last week, near-daily reports came in of human-triggered persistent slab avalanches on the January 30th weak layer, with the associated surface hoar layer taking both recreationalists and professionals by surprise. Reactivity has begun to taper but this buried weak layer should not be taken lightly as it may now present a low-probability, high-consequence problem. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks and on steep convexities. Check out this recent MIN report from the south of the region where the surface hoar is very prominent and shows propagating results in an extended column test. 

On Saturday in the North Colombia, a large natural persistent slab avalanche occurred on a south-facing aspect in the alpine, potentially as a result of warm temperatures and strong solar radiation. On Friday, large persistent slab avalanches were triggered with explosives on solar aspects in the alpine and treeline. 

Snowpack Summary

A light amount of new snow is expected to bond poorly to the old surface. This surface is comprised of near-surface faceting and in some areas, surface hoar growth overlying a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. 

Several weak layers exist in the upper snowpack including buried crusts, facets, and a prominent weak layer of buried surface hoar. This surface hoar has been the dominating feature in the past few weeks. It was buried in late January and exists 30 to 80 cm deep in the snowpack. The surface hoar is most prominent in sheltered openings at and below treeline.

The facet/crust layer that formed in early December is now buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. Humans are unlikely to trigger it, with perhaps the exception in thin, shallow snowpack areas. Check out the forecaster blog for more information.

Terrain and Travel

  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.

Régions couvertes