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Avalanche Forecast

Archived

Dec 20th, 2019–Dec 21st, 2019

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

Regions

Kootenay Boundary.

The powerful storm will continue to drop snow and blow strong wind. A natural avalanche cycle is likely underway and very dangerous avalanche conditions will continue into Saturday. Travel in avalanche terrain is not recommended.

Confidence

High -

Weather Forecast

FRIDAY NIGHT: Cloudy with heavy snowfall, accumulation 20 to 40 cm, strong to extreme southwest wind, alpine temperature -2 C, freezing level 1700 m.

SATURDAY: Cloudy with snowfall, accumulation 20 to 40 cm, strong to extreme southwest wind, alpine temperature -3 C, freezing level 1500 m.

SUNDAY: Cloudy with snowfall, accumulation 5 to 10 cm, light to moderate south wind, alpine temperature -5 C, freezing level 1000 m.

MONDAY: Cloudy with snowfall, accumulation 5 to 10 cm, light to moderate southwest wind, alpine temperature -5 C, freezing level 700 m.

Avalanche Summary

Many large persistent slab avalanches were triggered naturally and by explosives on Friday. This trend is expected to continue into the weekend during the storm.

Snowpack Summary

The storm will continue to hammer the region with about 20 cm of snowfall every 12 hours until Sunday morning. This snow will load multiple weak layers, including:

  • a feathery surface hoar layer buried around 50 to 80 cm beneath the new snow.
  • a surface hoar layer buried about 70 to 100 cm, with an associated melt-freeze crust on steep south aspects.
  • a complex layer of weak and sugary faceted snow, surface hoar, and melt-freeze crusts in the bottom half of the snowpack.

Given the weak nature of these layers, both natural and human-triggered avalanches will remain very likely to trigger given the substantial amount of new snow and strong wind forecast with this storm.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid exposure to overhead avalanche terrain, avalanches may run surprisingly far.

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.