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Avalanche Forecast

Archived

Dec 26th, 2020–Dec 27th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary.

Bits of new snow are keeping wind slabs fresh and will be especially sensitive to seeing the sun for the first time. 

We're being patient and sticking to conservative terrain for the next while until we have clear evidence that buried weak layers have stabilized. 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

Saturday night: A trace of new snow, moderate southwest wind, freezing level valley bottom.

Sunday: Clearing, light northwest wind, alpine temperature -8 C, freezing level 500 m.

Monday: Sunny, light northwest wind, alpine temperature -9 C, freezing level valley bottom.

Tuesday: Sunny, light northwest wind, alpine temperature -11 C, freezing level valley bottom.

Avalanche Summary

Many storm and persistent slab avalanches have been observed this week across the region. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and between 2000 and 2300 m. The most recent was a size 1 on Saturday near Nelson, triggered by a skier on a cross-loaded slope around treeline. Although avalanche activity is becoming smaller and more sporadic, the potential to trigger buried weak layers remains.

Snowpack Summary

5-10 cm of new snow may sit over surface hoar. Below, 30-40 cm of wind affected snow from the previous storm is taking some time to bond with underlying snow.

Two weak layers are buried around 50 to 100 cm deep. The layers are composed of feathery surface hoar and sugary faceted grains and they overly a hard melt-freeze crust. There has already been substantial avalanche activity on this layer from natural and human triggers. This layer remains a major concern, as humans may be able to trigger large and destructive avalanches on it. There has been less avalanche activity reported west of Castlegar but a similar snowpack exists so the possibility remains.

Another crust with associated faceted grains may be found near the base of the snowpack. There haven't been recent avalanches reported on this layer but it remains on our radar. The most likely place to trigger it would be from shallow, rocky terrain. 

Terrain and Travel

  • Be carefull around freshly wind loaded features.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid being on or under sun exposed slopes.

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.