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Avalanche Forecast

Archived

Dec 17th, 2020–Dec 18th, 2020

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

Regions

Northwest Inland.

If forecast snowfall amounts add up on Friday storm slabs may be reactive, especially on northeast to southeast slopes lee of the wind. Fresh avalanches, stiff snow, cracking and whumping are all indicators of a slab avalanche problem.

Confidence

Low - Uncertainty is due to the limited number of field observations. Forecast snowfall amounts are uncertain.

Weather Forecast

Overnight Thursday: Snow 5-10 cm with strong West winds and freezing levels 500 m.

Friday: Snow 5-10 cm with strong southwest wind. Alpine temperatures near -2 and freezing levels 1100 m.

Saturday: Snow 10 cm. Strong southwest wind and freezing levels near 1000 m.

Sunday: Mix of sun and cloud, windy and freezing levels 900 m.

Avalanche Summary

No new avalanches reported on Thursday.

A wind slab avalanche likely stepped down to the weak faceted grains described in the snowpack summary, forming a large avalanche near Smithers earlier this week. With forecast new snow, strong winds, and rising freezing levels avalanche danger will likely be on the rise.

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. 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

  • Watch for fresh storm slabs building throughout the day.
  • 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

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.