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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.
Alpine
Natural avalanches possible, human triggered probable.
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

Northwest Inland.

The primary concerns are new wind slabs forming up high and the potential of triggering buried weak layers.

Confidence

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

Weather Forecast

WEDNESDAY NIGHT: Partly cloudy, 10 to 20 km/h west wind, alpine temperature -8 C.

THURSDAY: Cloudy, 20 to 40 km/h southwest wind, alpine temperature -6 C.

FRIDAY: Cloudy with snowfall, accumulation 15 cm, 40 to 60 km/h southwest wind, alpine temperature -7 C.

SATURDAY: Cloudy with snowfall, accumulation 10 cm, 60 km/h southwest wind, alpine temperature -6 C.

Avalanche Summary

The latest reported avalanches were from last weekend, indicating a good amount of wind slab avalanche activity. Looking forward, wind slab activity may continue with elevated winds and some new snow in the forecast. The possibility also remains of triggering deeper weak layers, where they exist.

Snowpack Summary

Up to 5 cm of new snow overlies wind-affected terrain in the alpine and potentially a weak and feathery surface hoar layer, particularly in sheltered treeline terrain. This amount of snow in itself is not sufficient to form destructive avalanches, but thicker wind slabs may be found in exposed terrain features due to recent easterly wind that is forecast to switch to southwesterly.

Around 50 to 100 cm deep, a hard melt-freeze crust from early December may have weak and sugary faceted grains around it. The last reported avalanche activity on this layer was December 17 and 19.

The early-November melt-freeze crust may be found near the base of the snowpack and have weak faceted grains around it. The last reported avalanche activity was near Smithers on December 22. The most likely terrain to trigger it would be in shallow and rocky alpine areas.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

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.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.