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Avalanche Forecast

Archived

Dec 31st, 2020–Jan 1st, 2021

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

Regions

Northwest Coastal.

A powerful storm will impact the region, forming new slabs and loading buried weak layers. Conservative terrain travel will be key as well as avoiding avalanche terrain during periods of rapid loading and/or if you find more than 30 cm of snow accumulation.

Confidence

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm with the most along the west of the region, 60 km/h southwest wind, alpine temperature -3 C, freezing level 900 m.

FRIDAY: Cloudy with snowfall, accumulation 10 to 20 cm with the most along the west of the region, 40 to 60 km/h southwest wind, alpine temperature -2 C, freezing level 1000 m.

SATURDAY: Cloudy with snowfall, accumulation 20 to 40 cm, 60 km/h southwest wind, alpine temperature -5 C.

SUNDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 40 km/h southwest wind, alpine temperature -6 C.

Avalanche Summary

An avalanche cycle may occur at some point in the coming days, once sufficient snow loads the buried weak layers described in the snowpack summary. Avalanches could be triggered naturally or by riders and the result may be very destructive.

Snowpack Summary

A hefty storm is forecast to impact the region for the coming days. Up to 40 cm of snow may accumulate by Friday afternoon, particularly along the western side of the region. The snow will come with strong southwest wind, which will rapidly form wind slabs in exposed terrain. All of this snow will load a layer of surface hoar that was buried 10 to 20 cm prior to this storm. The surface hoar was reported as being widespread prior to burial and it may sit on a melt-freeze crust from warm air on Boxing Day and/or from sunny skies.

Another weak layer surface hoar may be found around 30 to 60 cm deep. The most likely places to find this layer would be in terrain features sheltered from wind effect.

Around 100 to 200 cm deep, a hard melt-freeze crust from early December may have weak and sugary faceted grains around it. These weak layers are likely the culprit of recent avalanche activity in the Nass Valley, Sterling, and Beaupre riding areas.

The early-November melt-freeze crust is over 200 cm deep and may have faceted grains above it in parts of the region, particularly in the north. The last reported avalanche activity was near Ningunsaw on December 11.

Terrain and Travel

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Be careful to keep storm day fever from luring you out into bigger terrain features.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.

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.

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.