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Avalanche Forecast

Archived

Dec 6th, 2021–Dec 7th, 2021

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 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.

Regions

Northwest Inland.

Choose terrain sheltered from the wind. Fresh wind slabs are forming over crusts and old wind slab. 

Avoid thin, rocky start zones. Deep weak layers are hard to trigger right now, but the resulting avalanche could be very large. 

Confidence

Moderate - Uncertainties in both the snowpack structure and the weather forecast limit our confidence.

Weather Forecast

Monday Night: Scattered clouds. No new snow expected. Variable light winds. Alpine low around -8, a temperature inversion may mean colder temperatures in the valleys.

Tuesday: Overcast. 5-10 cm of snow expected. Moderate to strong southwest winds. Alpine temperatures above -10 C with possible temperature inversion.

Wednesday: Mostly cloudy. 0-5 cm of snow expected. Strong southwest winds. Inversion breaking down. Alpine temperatures around -13. 

Thursday: Partly Cloudy. Possible trace of snow. Moderate to strong west winds. Alpine temperatures around -13.

Avalanche Summary

On saturday, a size 3 avalanche was reported in the Hankin-Evelyn area, failing near the ground. This has us thinking about the potential for a deep persistent weak layer.

This Mountain Information Network (MIN), post (and the two others pinned near it), paint a great picture of the recent conditions at Hankin-Evelyn.

Reports in the region remain limited. A lack of information may not actually mean there is a lack of avalanche activity. 

Snowpack Summary

There are recent reports of large to very large avalanches running on or near the ground in Bear Pass, Ningunsaw, in the Nass River Valley (northwest of Terrace), and around Smithers. We don't know how widespread this problem may be, or if all events reflect the same avalanche problem, but we are definitely keeping an eye on it, and would be avoiding large features and areas with thin to thick snowpack transitions for now. 

This snowpack summary is mostly speculative, as there is very little information in this region at the moment:) If you have been getting out in the backcountry, we'd love to see a photo or a quick story of your day posted to the Mountain Information Network. 

Due to recent, variable winds, you may find wind slabs on many aspects, and on both sides of ridges. Some exposed areas may be stripped back to the Nov 30/Dec 1 Crust. This crust has been reported up to 1600 m in the south end of the region.

There have been widespread reports of surface hoar forming in the Northwest Coast region. The weather inland has also been ideal for surface hoar growth, so watch for where it's on the surface, or think about where it might be lurking once it's buried. This could be a touchy new sliding layer when it gets buried on Tuesday, especially where it will be sitting on a crust.

Treeline snow depths are estimated to be 100-150 cm.

Terrain and Travel

  • Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
  • Keep in mind the crust offers an excellent bed surface for avalanches.
  • Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.

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.