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Avalanche Forecast

Archived

Dec 23rd, 2021–Dec 24th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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 simple, well supported terrain without convexities. It's a bit too soon to jump into bigger, steeper, open terrain. Slabs formed during the storm can still avalanche under the weight of a rider.

Confidence

Low - Uncertainty is due to the limited number of field observations. We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Thursday Night: Mostly cloudy, clearing Friday morning. 2-8 cm of snow expected. Light to moderate southwest winds, trending to strong at high elevations in the far south end of the region. Freezing level at valley bottom. 

Friday: A mix of sun and cloud. 0-2 cm of snow expected. Up to 5 cm in the Coquihalla area. Light north winds, trending to southwest at higher elevations. Temperature @ 1500m dropping to around -13 C.

 

Saturday: Mostly cloudy. 2-5 cm of snow expected. Light northeast winds trending to strong southwest 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 southeast at higher elevations. Temperature @ 1500 m around -25 C.

Avalanche Summary

No new avalanches were reported on Thursday, but not many professional operations or recreators have reported recently. Remember that a lack of reports does not necessarily mean a lack of avalanche activity.

In neighbouring regions with similar storm totals, the storm slabs were reported to be reactive, with avalanche control producing many size 2 avalanches. Also a couple of smaller, skier triggered avalanches were reported in steep, unsupported terrain.

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

30-60 cm of storm snow fell Tuesday night through Thursday, with moderate to strong south through southwest winds. Expect the new snow to be deeper and slabbier on leeward slopes.

This new snow sits on a variety of snow surfaces: variable wind slabs and hard wind-scoured surfaces in terrain exposed to the wind, and preserved powder and possible surface hoar in sheltered areas. 

This Mountain Information Network (MIN) post from Tuesday paints a great picture of the conditions around the Wendy Thompson hut before the bulk of the storm.

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

  • 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.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • 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.