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Avalanche Forecast

Archived

Dec 16th, 2020–Dec 17th, 2020

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

Regions

Northwest Inland.

Up to 15 cm of new storm snow and strong southwest wind has likely formed fresh new wind slabs on northeast though southeast slopes and behind terrain features. Stiff snow and cracking are indicators of a potential wind slab avalanche problem.

Confidence

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

Weather Forecast

A brief period of high pressure will bring a mix of sun and cloud to the region on Thursday and Friday. Ridgetop wind will be strong from the southwest with freezing levels as high as 1100 m. The next frontal system is expected this weekend bringing new snow, strong to extreme winds and rising freezing levels near 1500 m.

Avalanche Summary

No new avalanches reported on Wednesday.

A wind slab avalanche likely stepped down to the weak faceted grains described in the snowpack summary, forming a large avalanche near Smithers within the past few days.

Data in this region is very sparse. Please consider sharing your observations to the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter.

Snowpack Summary

Up to 15 cm of new snow and strong wind from the southwest have built the freshest wind slabs on the northeast facing slopes at treeline and in the alpine. Older wind slabs may still be found on other slopes from the East winds early this week. These slabs may overly a melt-freeze crust from early December, which may have weak and sugary faceted grains growing around it.

At the base of the snowpack sits the early-November crust with weak faceted grains below. These faceted grains have formed large avalanches in both the south and north of the region within the past week.

Snowpack depths vary substantially with aspect, elevation, and wind exposure. Below treeline the terrain may still be below the threshold for avalanches. 

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.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

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.