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Avalanche Forecast

Archived

Dec 24th, 2021–Dec 25th, 2021

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

Regions

South Coast Inland.

Choose your terrain carefully, and avoid thin, rocky start zones. Storm slabs will be most reactive at ridge crests and steep rolls, and an unpredictable persistent slab problem is still lurking. 

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

Friday Night: Partly cloudy. 0-5 cm of snow expected. Light north winds trending to moderate southwest at higher elevations. Temperature @ 1500 m dropping to around -15 C.

 

Saturday: Mostly cloudy, possible periods of sun in the afternoon. 5-10 cm of snow expected. Light north winds trending to strong south at higher elevations. Temperature @ 1500 m dropping to around -17 C.

Sunday: A mix of sun and cloud. 0-2 cm of snow expected. Light to moderate north winds, trending to east at higher elevations. Temperature @ 1500 m around -25 C.

Monday: Sunny in the morning, partly cloudy by the afternoon. No new snow expected. Light northwest winds, trending to strong at higher elevations. Low temperature @ 1500 m around -25 C.

Avalanche Summary

On Friday, a skier triggered size 2.5 persistent slab avalanche was reported in the backcountry near Blackcomb. It was around 110 cm deep, in a northwest facing feature around 2100 m. Last week's forecaster blog is still relevant. 

No new avalanches were reported in this region on Thursday or Friday.

In neighbouring regions with similar storm totals, the storm slabs were reported to be reactive, with avalanche control producing many size 2 avalanches. 

Storm slab avalanches have the potential to step-down to recently reactive buried weak layers, with the potential to produce very large, destructive avalanches.

Snowpack Summary

10-20 cm of new, low density snow overlies 30-60 cm of snow that fell Tuesday night through Thursday, with moderate to strong south through southwest winds. Expect the wind transported snow to be deeper and more reactive on leeward slopes. Watch for local variation in wind directions. For example, this Mountain Information Network (MIN) Post describes windslabs at and above treeline from northwest winds in the Cayoosh Pass area. 

Also from the Cayoosh area, here is another MIN report looking deeper into the snowpack.

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 lower alpine and treeline elevations, between 1500-2100 m. Large size 2 and 3 avalanches on this persistent slab problem 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

  • Start with simple terrain and gather information before thinking about more committing features.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.