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Avalanche Forecast

Archived

Jan 10th, 2021–Jan 11th, 2021

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

Regions

Kootenay Boundary.

Heightened avalanche conditions exist on wind-loaded slopes and in steep, rocky terrain. The likelihood of triggering deeply buried weak layers is reducing but the consequence of doing so remains high.

Confidence

High -

Weather Forecast

SUNDAY NIGHT: Cloudy with isolated flurries, 20 km/h southwest wind, alpine temperature -6 C.

MONDAY: Cloudy with snowfall, accumulation 5 cm, 40 km/h southwest wind, alpine temperature -6 C.

TUESDAY: Cloudy with snowfall, accumulation 10 to 20 cm, 40 km/h southwest wind, alpine temperature -4 C.

WEDNESDAY: Cloudy with snowfall then clearing, accumulation 15 to 25 cm, 30 km/h west wind, alpine temperature -5 C.

Avalanche Summary

A few small wind slab avalanches were triggered by riders on Saturday. They occurred on north to northwest aspects and around 2000 m.

Of note, a naturally-triggered size 3 deep persistent slab avalanche released on a southeast aspect at 2200 m in the Rossland range last Tuesday or Wednesday. The avalanche likely failed on the weak layers described in the Snowpack Summary and scrubbed to ground. Persistent slab avalanche activity has quieted in the past few days since this report. Although the likelihood of triggering these layers has reduced, the consequence of doing so remains high. 

Snowpack Summary

Lingering wind slabs may be found at higher elevations from strong southwest wind. In sheltered areas, recent new snow may overlie surface hoar. 

Two weak layers are buried in close proximity to one another. They are 70 to 100 cm deep around Nelson and 50 to 80 cm deep around Rossland and other western parts of the region. The layers are composed of surface hoar and faceted grains and they overlie a hard melt-freeze crust. Many MIN reports describe these layers and their snowpack test results. The results suggest that it remains possible for riders to trigger these layers.

Another layer of faceted grains above a melt-freeze crust that formed in early November is upwards of 200 cm below the surface. This has been the suspected failure layer of a few very large avalanches that released last week in the Rossland range.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Cornice failure may trigger large avalanches.

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.