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Avalanche Forecast

Archived

Jan 1st, 2021–Jan 2nd, 2021

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

Regions

Northwest Inland.

A stormy period is forecast for the weekend, increasing avalanche danger. Conservative terrain travel is needed during this time, with avoidance of avalanche terrain during periods of rapid snow accumulation or with signs of instability.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 5 to 10 cm, 60 km/h southwest wind, alpine temperature -6 C.

SATURDAY: Cloudy with snowfall, accumulation 10 to 15 cm, 70 km/h southwest wind, alpine temperature -5 C, freezing level 1000 m.

SUNDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 60 km/h southwest wind, alpine temperature -7 C.

MONDAY: Cloudy with snowfall, accumulation 5 cm, 40 km/h south wind, alpine temperature -8 C.

Avalanche Summary

Avalanche activity is expected to spike during this stormy period, as slabs form and sufficient snow loads the buried weak layers described in the snowpack summary. Avalanches could be triggered naturally or by riders and the result may be very destructive.

Snowpack Summary

Around 20 cm of snow has accumulated in much of the region so far and the snow is forecast to continue to fall over the weekend. Storm totals could reach 40 cm by Saturday afternoon. Storm and wind slabs are likely forming rapidly and they may overly a weak and feathery surface hoar layer, particularly in sheltered treeline and below treeline terrain.

Around 50 to 100 cm deep, a hard melt-freeze crust from early December may have weak and sugary faceted grains around it. The last reported avalanche activity on this layer was around December 21. The likelihood of triggering this layer is expected to increase during this stormy period.

The early-November melt-freeze crust may be found near the base of the snowpack and may have weak faceted grains around it. The last reported avalanche activity on this layer was near Smithers on December 22. The most likely terrain to trigger it would be in shallow and rocky alpine areas.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.