Avalanche Forecast

Issued: Dec 27th, 2021 4:00PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada shorton, Avalanche Canada

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Reverse wind-loading and a buried weak layer warrant careful terrain choices. Seek out softer conditions in wind-sheltered areas.

Summary

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

Cold arctic air sits over the region with little change in weather conditions over the next few days.

MONDAY NIGHT: Mostly clear skies, no significant precipitation, light wind from the northwest, treeline temperatures around -20 C.

TUESDAY: Sunny with a few clouds, no precipitation, light wind from the north, treeline temperatures around -15 C.

WEDNESDAY: Mix of sun and cloud, no precipitation, moderate wind from the northeast with gusts to 50 km/h, treeline temperatures around -15 C.

THURSDAY: Cloudy, light flurries with 5 cm of low density snow, light to moderate wind from the northwest, treeline temperatures around -12 C.

Avalanche Summary

Over the weekend there was evidence of wind slab avalanches becoming reactive at upper elevations. There were several small (size 1) human triggered slabs including this one from Gin Peak that illustrates how shifting wind patterns can form slabs in atypical locations.

Cornices are large and looming and have the potential to trigger large avalanches on slopes below. Several large (up to size 2) cornices have been both human-triggered and explosive-triggered this week.

It remains possible to human-trigger large persistent slab avalanches, particularly in shallow snowpack areas at treeline and low alpine elevations. On Friday, a large (size 2.5) persistent slab avalanche was skier-triggered in the backcountry near Blackcomb. It released 110 cm deep on the early December crust layer on a northwest facing slope around 2100 m in a shallow rocky start zone.

Snowpack Summary

20 to 35 cm of low density snow can be found in many locations, although gusty conditions have been causing highly variable wind loading patterns. On Sunday, there were some reports of calm conditions in the alpine with minimal wind affect while neighbouring areas reported extensive wind affect. The current weather conditions could quickly form reactive slabs on leeward slopes, including unusual cross-loading or reverse-loading patterns in wind-exposed areas. Sensitivity to triggering will be greatest near ridge crests and roll-overs. Monitor for changing slab conditions as you move into wind-exposed terrain, and give cornices a wide berth.

A concerning weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 100-200 cm). This layer has been most reactive at treeline and low alpine elevations, between 1500-2100 m. Large (size 2-3) avalanches have been reported recently on this layer. This problem is particularly hard to predict and tricky to manage. Get more details and photos in our forecaster blog

Terrain and Travel

  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.

Problems

Wind Slabs

An icon showing Wind Slabs

Winds have shifted from south to north with an ample supply of light, cold snow to drift into reactive slabs. Watch for unusual cross-loading or reverse-loading patterns in wind-exposed areas, and anticipate reactive wind slabs on a variety of aspects.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

A layer of weak facets (sugary snow) can be found down 100-200 cm near a crust that formed in early December that remains possible to trigger. Cornice falls or wind slabs in motion may step down to this layer and trigger large destructive avalanches. It is more likely to human trigger this persistent slab in thin snowpack areas at elevations between 1500-2100 m. 

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2 - 3

Valid until: Dec 28th, 2021 4:00PM