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Avalanche Forecast

Archived

Dec 22nd, 2021–Dec 23rd, 2021

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
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.

Regions

Sea To Sky.

Recent major storm has develop significant storm slabs that remain reactive with the potential to step-down and trigger deeper buried weak layer. Avoid avalanche terrain and wait for conditions to improve.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Snow continues as moisture will persist in the extreme south of the province, favouring additional snowfall for the South Coast mountains.

Wednesday night: Snow, heavy at times, 25 to 40 cm, strong southerly winds, low treeline temperatures near -7 C with freezing level going down to valley bottom.

Thursday: Mainly cloudy with isolated flurries, 2-4 cm, light to moderate westerly winds, high treeline temperatures near -10 C with freezing level at valley bottom.

Friday: Flurries, 5 cm, light to moderate easterly winds, high treeline temperatures near -10 C with freezing level at valley bottom.

Saturday: Flurries, 5 to 10 cm, light to moderate easterly winds, high treeline temperatures near -12 C with freezing leval at valley bottom.

Avalanche Summary

A few wind slab avalanches triggered by skiers have been reported Tuesday in Pemberton area. With additional storm snow and strong southwesterly winds, we are expecting natural avalanche activity to continue on Thursday. Storm slabs avalanches have the potential to step-down to recently reactive buried weak layers, with the potential to produce very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below. 

Snowpack Summary

The ongoing storm has the potential to add 70 to 100 cm to the 30 to 50 cm layer of settling snow from last weekend's storm. All this new snow sits on a variety of snow surfaces, hard wind-scoured surfaces, preserved powder, and possible surface hoar in sheltered areas. Strong southerly winds will continue to redistribute the storm snow into dense wind slabs on leeward terrain features.

A culprit weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (down 100-200 cm). This layer seems 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 over the past few days. This problem is particularly hard to predict and tricky to manage. Given the rapid load from the storm and wind, this persistent slab problem requires to scale back and wait for conditions to improve. Get more details and photos in our forecaster blog. 

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Give the new snow time to settle and stabilize before pushing into bigger terrain.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.

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.