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Avalanche Forecast

Archived

Jan 16th, 2020–Jan 17th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary.

Recent wind slabs exist on a wide range of aspects at higher elevations. Choose terrain with the expectation that a smaller wind slab could trigger a deeper weak layer in the snowpack.

Confidence

Moderate -

Weather Forecast

Thursday night: Cloudy with easing flurries bringing 5-10 cm of new snow. Light to moderate southwest winds easing and shifting west.

Friday: Broken cloud cover. Light to moderate west or southwest winds. Alpine temperatures around -12.

Saturday: Cloudy with scattered flurries bringing about 5 cm of new snow. Light to moderate south winds. Alpine high temperatures around -7.

Sunday: Cloudy with isolated flurries and a trace of new snow. Light to moderate southwest winds. Alpine high temperatures around -3.

Avalanche Summary

No new persistent slab avalanches were observed on Tuesday or Wednesday, but this region has been a hot spot for recent persistent slab avalanche activity. A number of large natural avalanches up to size 3 were reported on east, southeast and south facing slopes above 2000 m in the Rossland area Monday with crowns up to 100-150 cm in depth.

In the rest of the region both natural and explosive controlled avalanches up to size 2.5 were observed on all aspects above 1800 m. Many avalanches failed on the December 27th Surface Hoar and one avalanche on a north/northeast facing slope at 1800 m involved the mid November facets.

On Sunday the bulk of the avalanche activity was limited to loose dry avalanches but a spooky avalanche was remote triggered by a group of skiers, more details and photos in this MIN report.

Snowpack Summary

Stormy weather over the past several days brought 35 to 65 cm of snow to the region. Each snowfall and interval in between has been characterized by variable wind ranging from moderate to strong and shifting from south to north and back again.

As a result, higher elevations have formed a variable array of old and new, fresh and buried wind slabs across all aspects while sheltered lower elevations have seen mainly increasing depths of low density snow.

As new snow continues to accumulate, concern is increasing for weak layers of surface hoar found around 70 to 130 cm deep. These layers have been active as recently as Monday and may reach a more widespread tipping point, even though they are gradually gaining strength. These layers are especially concerning in steep, large terrain features and shallow rocky areas.

The base of the snowpack is also weak in parts of the region where it consists of sugary faceted snow around a melt-freeze crust.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.