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Avalanche Forecast

Archived

Dec 20th, 2022–Dec 21st, 2022

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.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Moyie, St. Mary, Kokanee, Retallack, Valhalla.

Use extra caution at treeline where persistent slab avalanches are more likely. Make conservative decisions, even small accidents can have big consequences during periods of cold temps and short days.

Confidence

Moderate

Avalanche Summary

A few natural persistent slab avalanches up to size 2.5 were observed yesterday. These avalanches likely released on Sunday on the mid November layer at treeline.A couple of natural wind slabs up to size 1.5 were also observed in the alpine on northeast aspects on Monday.

Snowpack Summary

On Tuesday new snow and moderate winds could form new wind slab on north and east aspects. A new surface hoar layer on sheltered features and a sun crust on south facing terrain is buried down around 15cm.

The snow becomes slightly more consolidated after the above mentioned layer until around 50cm below the surface where another weak layer, created in early December, can be found. This layer is made up of surface hoar in sheltered areas and a thin sun crust in open south-facing terrain.

The layer that is still the main concern, is that of mid-November. It is made up of large surface hoar crystals, facets, and a melt-freeze crust and can be found up to 80 cm deep. This layer has been reactive at treeline between 1700 to 2200 m, on all aspects.

Below the mid-November layer is a generally weak, faceted snowpack. Snowpack depths average 80 to 160 cm in the alpine.

Weather Summary

Tuesday Night

Flurries bringing trace amounts of new snow with light northwest winds and a Low of -23 at 1800m.

Wednesday

Mostly sunny with no new snow expected. Light easterly winds and a high of -21 at 1800m.

Thursday

Mostly sunny with no new snow expected. Light variable winds and a high of -23 at 1800m.

Friday

Cloudy with around 5cm of new snow expected. Southwest winds increasing throughout the day. High of -17 at 1800m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for surprisingly large avalanches due to deeply buried weak layers.
  • Don't let the desire for deep powder pull you into high consequence 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.