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Avalanche Forecast

Archived

Jan 20th, 2021–Jan 21st, 2021

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

Regions

Kootenay Boundary.

Wind slabs may remain triggerable. Be careful in drifted areas and assess open slopes and rollovers where a weak layer may be preserved.

Confidence

High -

Weather Forecast

Wednesday night: Partly cloudy, light wind, freezing level valley bottom.

Thursday: Mix of sun and cloud, light wind, treeline temperatures around -8 C.

Friday: Sunny, light wind, treeline temperatures around -10 C.

Saturday: Sunny, light to moderate northwest to southwest wind, treeline temperatures around -13 C.

Avalanche Summary

In the last few days, skiers have triggered a few small wind slabs (size 1) at wind loaded ridgecrests.

Since last week's storm a few natural avalanches are suspected to have run on the surface hoar 20-50 cm down, including a size 2.5 storm slab out of a northwest facing gully feature around 2000 m near Nelson.

Snowpack Summary

Previous wind has likely redistributed 10-15 cm of recent snow into wind slabs in lee terrain features at upper elevations. This snow may sit over a widespread crust that extends up to around 2000 m, or large surface hoar crystals in wind sheltered areas above the crust elevation. In areas such as Rossland, the thick crust caps the snowpack to mountaintop, making travel difficult.

A layer of surface hoar may be found 20-50 cm below the surface, particularly in areas around Nelson. Some recent avalanches have run on this layer and where it has been found in snow profiles, it has been producing moderate to hard planar test results.

A couple of crusts with weak faceted grains overtop are buried deep within the snowpack. The upper layer is 80 to 130 cm deep and the lower is near the ground. A few large avalanches ran naturally on these layers last week near Rossland. More recently, some large cornice falls have have been good slope testers. Some triggered storm slabs but none stepped down to these deeper layers. While this is a good indicator for stability, the potential may linger for triggering a deep slab in steep, rocky, thin snowpack areas. 

Terrain and Travel

  • Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.