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Avalanche Forecast

Archived

Jan 4th, 2020–Jan 5th, 2020

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

Regions

South Coast Inland.

Stormy conditions continue on Sunday, with the most snowfall expected in the south of the region. Travel in avalanche terrain is not recommended. A touchy weak layer in the north of the region requires particular caution.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

SATURDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm near Coquihalla and 5 to 10 cm elsewhere, moderate to strong southwest wind, alpine temperature -7 C, freezing level 1000 m.

SUNDAY: Cloudy with snowfall, accumulation 20 cm near Coquihalla and 5 to 10 cm elsewhere, moderate to strong southwest wind, alpine temperature -7 C, freezing level 1000 m.

MONDAY: Cloudy with snowfall, accumulation 5 to 10 cm, moderate southwest wind, alpine temperature -7 C, freezing level 600 m.

TUESDAY: Cloudy with snowfall, accumulation 10 to 20 cm, moderate southwest wind, alpine temperature -3 C, freezing level 1300 m.

Avalanche Summary

Many large to very large avalanches were triggered in the region on Friday and Saturday. Some of them released in recent storm snow with crowns of 25 to 80 cm. Many avalanches in the north of the region released on the weak layer of faceted grains described in the snowpack summary. They were 50 to 120 cm thick and released on all aspects between 1800 m and 2300 m.

Snowpack Summary

Intense snowfall continues in the region, forming dangerous avalanche conditions. Snowfall amounts may reach 30 to 40 Saturday night into Sunday near Coquihalla and otherwise 20 cm of snow may accumulate in the region. This snowfall will add to the 30 to 60 cm from Friday. All of this snow is falling with strong southwest wind, redistributing it in exposed terrain. The snow may overly a touchy weak layer of feathery surface hoar, making storm slabs particularly touchy.

A persistent weak layer is present near the bottom of the snowpack in the northern half of the region (e.g., Duffey, Hurley). The weak layer of sugary faceted grains exists around a hard melt-freeze crust from mid-November, which is an indicative snowpack setup for large and destructive avalanches. The likelihood of natural and human-triggered avalanches on this layer remains elevated with the snow and wind loading occurring during this stormy period.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Make conservative terrain choices and avoid overhead hazard.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

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.