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Avalanche Forecast

Archived

Dec 14th, 2020–Dec 15th, 2020

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

Regions

Northwest Coastal.

Substantial snowfall is expected in the far south of the region but the track of the system may shift. Treat the danger as HIGH if you find more than 30 cm of snowfall accumulation.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

MONDAY NIGHT: Cloudy with snowfall, accumulation 15 to 25 cm near Kitimat and 5 to 10 cm for the remainder of the region, 40 to 60 km/h southwest wind, alpine temperature -4 C, freezing level 800 m.

TUESDAY: Cloudy with snowfall, accumulation 10 to 30 cm in the south of the region and 2 to 5 cm in the north, 60 km/h southwest wind, alpine temperature -4 C, freezing level 700 m.

WEDNESDAY: Cloudy with snowfall, accumulation 20 to 40 cm in the south of the region and 5 to 10 cm in the north, 40 to 60 km/h southwest wind, alpine temperature -5 C.

THURSDAY: Mix of sun and cloud with periodic snowfall, accumulation 5 cm, 20 to 40 km/h west wind, alpine temperature -7 C.

Avalanche Summary

A few naturally-triggered wind slab avalanches were observed around Bear Pass on Sunday. The last deep persistent slab avalanches released on December 11 in the north of the region near Ningunsaw.

Data in this region is very sparse. Please considering 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

The next snow storm is forecast for Tuesday, bringing substantial snowfall to the south of the region as well as strong southwest wind. Expect slabs to form during the storm, particularly in wind-affected terrain at and above treeline. The snow will fall onto previous wind-affected snow at higher elevations, potentially a layer of surface hoar in sheltered areas, and a crust at lower elevations.

The early-December crust is now down 100 cm in the alpine but close to the surface at and below treeline elevations. The early-November crust is buried around 100 to 200 cm at treeline elevations. The early-November crust may have weak and sugary faceted grains above it in parts of the region, which have produced large, full-depth avalanches in the past weeks. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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.