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Avalanche Forecast

Archived

Dec 19th, 2019–Dec 20th, 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 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.

Regions

Kootenay Boundary.

A powerful storm will impact the region Thursday night and into the weekend. Substantial snowfall and strong wind will create very dangerous avalanche conditions. Travel in avalanche terrain is not recommended until the snowpack stabilizes.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

THURSDAY NIGHT: Cloudy with heavy snowfall, accumulation 20 to 30 cm, strong to extreme southwest wind, alpine temperature -3 C, freezing level 1000 m rising to 1700 m.

FRIDAY: Cloudy with heavy snowfall, accumulation 30 to 50 cm, strong to extreme southwest wind, alpine temperature -2 C, freezing level 1700 m.

SATURDAY: Cloudy with snowfall, accumulation 40 to 50 cm, strong to extreme southwest wind, alpine temperature -2 C, freezing level 1700 m.

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

Avalanche Summary

A few small avalanches were triggered on Wednesday by skiers. Avalanche activity will likely increase Thursday night into Friday. A natural avalanche cycle is likely to occur during this storm.

Snowpack Summary

Around 50 to 80 cm of snow may accumulate Thursday night into Friday. 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 become very likely to trigger given the substantial amount of new snow and strong wind forecast with this storm.

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.