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Avalanche Forecast

Archived

Dec 19th, 2020–Dec 20th, 2020

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

Regions

Kootenay Boundary.

Snow and strong wind will form new slabs and continue to load an already touchy snowpack. An avalanche cycle may occur during Saturday night's storm and humans will surely be capable of triggering avalanches on Sunday.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

SATURDAY NIGHT: Snow, accumulation 15 to 25 cm, 60 to 80 km/h southwest wind, alpine temperature -5 C, freezing level 1200 m.

SUNDAY: Morning snowfall then clearing, accumulation 5 cm, 40 to 60 km/h northwest wind, alpine temperature -4 C, freezing level 1500 m.

MONDAY: Snow, accumulation 15 cm, 20 to 30 km/h south wind, alpine temperature -7 C.

TUESDAY: Snow then clearing, accumulation 20 cm, 10 to 20 km/h northwest wind, alpine temperature -6 C.

Avalanche Summary

There have been many human-triggered avalanches from the past few days, often within the weak layer described in the snowpack summary. Riders have been reporting conditions as "unsettling', 'electric', 'super touchy', and 'running far'. Avalanches appear to have been reported on all aspects and at all elevation bands.

Avalanche activity is expected to continue on Sunday as new slabs are formed and the snow further loads the weak layers.

Snowpack Summary

Saturday night's snowfall will accumulate with strong southwest wind, forming wind slabs in exposed terrain. These will overly previous storm layers within the top 40 cm of the snowpack.

This snow will continue to load a weak layer around 30 to 60 cm deep. The layer may be composed of feathery surface hoar or sugary faceted grains and they overly a hard melt-freeze crust. Riders have reported avalanche activity and whumpfing on this layer as well as surprising snowpack test results. This layer remains a major concern, as humans may be able to trigger large and destructive avalanches on it.

Another crust with associated faceted grains may be found near the base of the snowpack. There have been no 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

  • Travel in alpine terrain is not recommended.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.

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.