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Avalanche Forecast

Archived

Dec 25th, 2021–Dec 26th, 2021

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

Regions

Kootenay Boundary.

Loose, dry snow is providing excellent conditions. Assess conditions as you travel, reactive slabs may be found where snow feels stiff or more cohesive.

Confidence

Moderate -

Weather Forecast

Saturday night: Scattered flurries, 5-10 cm. Moderate gusty southerly winds. Treeline temperatures near -10 and freezing levels at the valley bottom.

Sunday: Unsettled and windy with scattered flurries, up to 5-10 cm. Moderate south wind and temperatures dropping from -13.

Monday: Cold and cloudy with sunny breaks. Light southwest wind and a high of -18.

Tuesday: Cold, mostly cloudy, and isolated flurries. Light north wind and a high temperature of -20.

Avalanche Summary

Oh Friday, small (size 1-1.5) slab avalanches were reactive to skiers. Explosives triggered larger (size 2.5) avalanches including 2 avalanches which failed on the early December crust with crowns 80-120 cm deep.

On Thursday, several natural and skier-controlled storm slab avalanches up to size 2 were reported, and explosives triggered slab avalanches to size 2.5; avalanches ranged from 20-60 cm deep.

Snowpack Summary

25-60 cm cold, dry snow arrived Christmas with light southwest wind, ongoing flurries are expected through Sunday. Cold temperatures and calm winds will keep snow light and fluffy, but snow will be redistributed easily with little wind. Sluffing is to be expected in steep terrain.

In total, 30-70 cm snowfall over the week reportedly covered a thin freezing rain crust and a surface hoar interface, which has been responsible for recent storm slab avalanches.

A crust from early December is now 50-120 cm below the surface, and is found up to 2300 m. A layer of weak facets (sugary snow) has been reported above and below this crust, and is the layer of concern in our persistent avalanche problem.

The lower snowpack is composed of several early-season crusts. Snow depths at treeline average 150-200 cm. Below 1800 m the snowpack remains relatively shallow with 80-120 cm on average. The deepest snowpack can be found in the Kootenay Pass area.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Start with conservative lines and watch for clues of instability.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.