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

Regions

Sea To Sky.

Stormy conditions continue this weekend. Both natural and human-triggered avalanches are very likely, with the potential for very large avalanches to reach the valley bottom. Travel in avalanche terrain is not recommended, including travel in runout zones.

Confidence

High -

Weather Forecast

SATURDAY NIGHT: Cloudy with snowfall, accumulation 20 to 30 cm, moderate to strong southwest wind, alpine temperature -9 C, freezing level 800 m.

SUNDAY: Cloudy with snowfall, accumulation 20 to 40 cm, strong southwest wind, alpine temperature -7 C, freezing level 1000 m.

MONDAY: Cloudy with snowfall, accumulation 10 to 20 cm, moderate southwest wind, alpine temperature -7 C, freezing level 800 m.

TUESDAY: Cloudy with snowfall, accumulation 30 to 50 cm, moderate to strong southwest wind, alpine temperature -3 C, freezing level 1100 m.

Avalanche Summary

On Saturday, a large avalanche released on the weak layer described in the snowpack summary. The avalanche occurred in alpine terrain and had a slab thickness of 150 cm.

On Friday, many small storm slab avalanches were triggered naturally, by humans, and by explosives. 

Avalanche activity is expected to continue into Sunday as more snow accumulates.

Snowpack Summary

Intense snowfall continues in the region, forming dangerous avalanche conditions. Snowfall amounts may reach 40 to 60 cm Saturday night into Sunday, adding to the 30 to 70 cm from Friday. All of this snow is falling with strong southwest wind, redistributing it in exposed alpine and treeline areas. The snow may overly a touchy weak layer of feathery surface hoar, making storm slabs particularly touchy.

Near the bottom of the snowpack around 150 to 200 cm deep, sugary faceted grains and a hard melt-freeze crust exist 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 rapid loading occurring during this stormy period.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid the runout zones of avalanche paths. Avalanches could run full path.

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.