Avalanche forecast

North Columbia

Dec 23 – 24, 2020Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

 50 to 80 cm of new snow from the past week rests on a variety weak layers. It is best to adopt a conservative approach to terrain selection as the snowpack adjusts the load.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    There is lots of snow available for recent moderate to strong northwesterly winds to transport into alpine and treeline lee terrain.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2.5–3.5

    The last storm pushed the persistent slab problem over the tipping point resulting in very large avalanches Saturday & Sunday. The slab rests on a persistent weak layer which has the capacity to propagate avalanches across terrain features. Wind exposed features are expected to be particularly volatile.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

TUESDAY NIGHT: Broken cloud cover, moderate northwest wind, alpine temperature near -12 C.

WEDNESDAY: Scattered cloud cover, light to moderate west wind, alpine temperature near -6 C.

THURSDAY: Mainly sunny, light southerly wind, alpine temperature near -2 C with potential for a light alpine temperature inversion.

FRIDAY: Mix of sun and cloud, light southwest wind, alpine temperature near -5 C.

Avalanche Summary

Over the weekend a natural avalanche cycle took place with avalanches averaging size 1.5 to 2.5, but there were a few size 3 and even size 3.5's in the mix too. Many of the larger avalanches likely ran on persistent weak layers.

Snowpack Summary

60 to 100 cm of storm snow has fallen over the last week. Underneath this storm snow there is a sandwich of weak layers which are widespread throughout the region.

Just under the new snow, down about one meter below the surface is the mid December surface hoar. This layer has been failing naturally and has been quite sensitive to human triggering throughout the storm cycle. Large avalanches have been running on this interface connecting big terrain features. 

Below that lies the early December persistent weak layer, it's about 80 to 140 cm below the surface. This weak layer is a mixed bag that often presents as surface hoar and facets sitting on top of a stout supportive crust. This is a nasty weak layer, when avalanches fail on it, they have been large and destructive. Smaller avalanches in motion can step down to this one too. This weak layer is going to haunt us for the foreseeable future. 

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Carefully manage your exposure to overhead hazards while entering and leaving riding areas.

Regions covered