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Avalanche Forecast

Archived

Jan 24th, 2022–Jan 25th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

North Columbia.

Conditions may have improved, but be mindful that deep instabilities are still present. Avoid shallow or variable depth snowpacks and unsupported terrain features. 

Confidence

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

Weather Forecast

MONDAY NIGHT: Partly cloudy / Decreasing northwest wind / Low temperature -10 C / Freezing level at valley bottom.

TUESDAY: Increasing cloud / Light flurries / Light west wind gusting moderate / High temperature -6 C / Freezing level around 700 m.

WEDNESDAY: Cloudy with sunny periods / Light west wind gusting moderate / High temperature -8 C / Freezing level around 700 m.

THURSDAY: Mix of sun and clouds / Light northwest wind / High temperature -5 C / Possible temperature inversion / Freezing level around 500 m.

Avalanche Summary

On Sunday, warm temperature and strong solar radiation naturally triggered a large (size 2.5) deep persistent avalanche from steep rocky alpine features in the Selkirks. In the Monashees, a cornice fall was large enough to trigger an avalanche at the top of the track zone, which has propagated full path. It has likely involved the Dec 1 deep persistent layer.

Wind slabs have shown signs of surprising reactivity throughout the region, with a remote human trigger avalanche over a large convex rollover 100 m away, probably failing on a surface hoar layer. Numerous small accidentally triggered wind slabs were also reported on the same layer down 30-45 cm.

On Saturday, explosives near the Trans Canada triggered very large avalanches (size 2.5-3.5) failing on the early December facet/crust layer. This included a historical size 4.5 avalanche which started at ridgeline, created new trim lines, and destroyed mature timber. 

This past week numerous very large (size 2.5-3.5) deep persistent slab avalanches occurred in both the Selkirks and Monashees. These avalanches failed on the early December facet/crust layer, typically 100-150 cm deep. One notable pattern is that many of these avalanches released at relatively low elevations (1700 to 2000 m) in open clearings, burns, and slide paths. In many cases, they were triggered by smaller avalanches starting at higher elevations. This layer is likely to plague our snowpack for the remainder of the season and will be a low probability but extremely high consequence result if triggered.

Snowpack Summary

A variety of snow surfaces can be found: crusts at lower elevations and on solar slopes into the alpine, wind press and wind slabs in open and exposed terrain, and settling powder in sheltered areas. Surface hoar growth has also been reported.

The most recent snowfall covered a layer of surface hoar now down 20-30 cm, likely responsible for the most recent natural storm slab avalanches reported Jan 20-21. The upper snowpack (top 30-100 cm) has a variety of layers that may or may not be a problem. These layers include surface hoar and crusts buried during January snowfalls and facets buried at the start of January. While none of these upper layers are necessarily going to remain a long-lasting concern, there is uncertainty about their spatial distribution and their remaining reactivity after the warm event.

The primary weak layer that remains a widespread concern across the Columbia Mountains is a 100-200 cm deep crust/facet layer that formed in early December. There has been regular avalanche activity on this layer at all elevations for over a month. 

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.