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Avalanche Forecast

Archived

Dec 27th, 2021–Dec 28th, 2021

Alpine
Natural avalanches possible, human triggered probable.
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

South Coast Inland.

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

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the limited number of field observations.

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, moderate wind from the northwest, treeline temperatures around -22 C.

TUESDAY: Sunny with a few clouds, no precipitation, moderate wind from the northwest, treeline temperatures around -20 C.

WEDNESDAY: Sunny with a few clouds, no precipitation, moderate wind from the north with gusts to 60 km/h, treeline temperatures around -20 C.

THURSDAY: Cloudy, light flurries with 5 cm of low density snow, light to moderate wind from the northwest, treeline temperatures around -16 C.

Avalanche Summary

There have been regular reports of small to large (size 1-2) wind slab avalanches in the Duffey Lakes area over the past few days. These included some natural avalanches on south aspects, that were the direct result of reverse loading. Based on this pattern we can expect to find reactive wind slabs in unusual locations over the upcoming days.

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 in the neighbouring Sea-to-Sky region. 

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 in the Sea-to-Sky region. 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

20-30 cm of low density snow can be found in many locations, although gusty conditions have been causing highly variable wind loading patterns. The current weather 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 layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 70-150 cm). This layer has been particularly reactive at treeline and low alpine elevations, between 1500-2100 m. Large (size 2-3) avalanches have been reported recently in the neighbouring Sea-to-Sky region. 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.
  • Be especially cautious near rock outcroppings, on steep convexities and anywhere the snowpack feels thinner than average.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.