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Avalanche Forecast

Archived

Jan 12th, 2020–Jan 13th, 2020

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

Regions

Kootenay Boundary.

Snowfall is forecast to end by Monday morning. Moderate to strong west wind will form fresh slabs in lee terrain features throughout the day. If the wind affects below treeline elevations consider the avalanche danger Considerable at all elevation bands.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

SUNDAY NIGHT: Cloudy with snowfall, accumulation 10 to 15 cm, light westerly wind, alpine temperature -12 C, freezing level dropping to valley bottom. 

MONDAY: Mix of cloud and sun with isolated flurries, moderate to strong west wind, alpine temperature -20 C, freezing level below valley bottom.

TUESDAY: Mostly cloudy with isolated flurries, moderate westerly wind, alpine temperature -18 C, freezing level below valley bottom.

WEDNESDAY: Mostly sunny, moderate westerly wind, alpine temperature -20 C, freezing level below valley bottom.

Avalanche Summary

On Sunday, a remote skier triggered size 2 avalanche on a deeper weak layer was reported (see MIN report).

On Saturday, numerous large (size 2) storm slab avalanches were triggered by explosives. Several small (size 1) and large (size 2) storm slab avalanches were triggered by skiers. A few small (size 1) natural storm slab avalanches were reported. 

On Friday, several skier triggered slab avalanches were reported up to size 2. Some of these avalanches were triggered remotely. Several small (up to size 1.5) natural avalanches were observed.

On Thursday, no new avalanches were reported, but one small (size 1) explosive triggered avalanche.

Snowpack Summary

The storm of the last days brought more than 40 cm of snow which partly fell with moderate to strong southwest wind. The formed slabs are sensitive to human triggers, particularly in exposed lee terrain features. More recent snow might hide slabs and make it trickier to navigate around them.

Deeper in the snowpack, a few layers of weak and feathery surface hoar may still be found around 70 to 130 cm deep. It is unclear whether they are still problematic and if so, how long they will be so for. The base of snowpack is also weak in parts of the region, where it consists of sugary faceted snow around a melt-freeze crust. Until these weak layers can be ruled out, best to travel conservatively.

Terrain and Travel

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Watch your sluff: it may run faster and further than you expect.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

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.