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Avalanche Forecast

Archived

Dec 30th, 2020–Dec 31st, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
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, 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.

Concern remains for the persistent weak layers that exist in the top 80 cm of the snowpack. Persistent weak layers can be very difficult to manage, so a conservative approach to terrain is important.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

WEDNESDAY NIGHT - Mainly cloudy with scattered flurries, up to 5 cm / southwest wind, 20-30 km/h / alpine low temperature near -6 

THURSDAY - A mix of sun and cloud with isolated flurries / light northwest wind / alpine high temperature near -5 

FRIDAY -Flurries, 5-10 cm, with another 10-15 cm Friday night / southwest winds 25-50 km/h / alpine high temperature near -4

SATURDAY - Flurries, 5-10 cm, with another 15 cm Saturday night / southwest wind, 40-60 km/h / alpine high temperature near -2 / freezing level 1300 m

Avalanche Summary

There were a few size 1 storm slab avalanches reported near Big White on Wednesday.

There was one explosives triggered size 1 cornice avalanche reported near Rossland on Monday.

Many storm and persistent slab avalanches were observed last week. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and at elevations between 2000 and 2300 m. Although avalanche activity appears to have diminished, I wouldn't rule out the possibility of seeing more persistent slab avalanches.

Snowpack Summary

Stormy weather on Wednesday brought 5-10 cm of new snow and may have form new wind slabs in leeward terrain. 

Two weak layers are buried in close proximity to one another. They are 50-80 cm deep around Nelson and 30-50 cm deep around Rossland and other western parts of the region. The layers are composed of feathery surface hoar and sugary faceted grains and they overlie a hard melt-freeze crust. 

There was substantial avalanche activity on these layers prior to Christmas from natural and human triggers. Although reports of such avalanches have been dwindling, these weak layers remain a concern, as they can produce large and destructive avalanches.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

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.

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.