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Avalanche Forecast

Archived

Dec 30th, 2020–Dec 31st, 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 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.

Regions

Northwest Coastal.

The primary concerns are new wind slabs forming up high and the potential of triggering buried weak layers.

Confidence

High -

Weather Forecast

WEDNESDAY NIGHT: Partly cloudy, 10 to 20 km/h northwest wind, alpine temperature -4 C.

THURSDAY: Cloudy, 20 to 40 km/h southwest wind, alpine temperature -4 C.

FRIDAY: Cloudy with snowfall, accumulation 20 to 40 cm, 40 to 60 km/h southwest wind, alpine temperature -4 C.

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

Avalanche Summary

The most prominent recent avalanche activity includes human-triggered avalanches north of Terrace. It is suspected that they released on the weak layers described in the snowpack summary. The likelihood of humans triggering similar avalanches remains. Check out these three MIN's for further information: here, here, and here.

Otherwise, a few small (size 1) storm slab avalanches were triggered naturally and by explosives in the top 5 to 15 cm of the snowpack. 

Snowpack Summary

Around 10 to 15 cm of snow fell on Wednesday with moderate northeast wind that is forecast to shift to the southwest. Expect to find wind slabs in exposed terrain features. The snow may overly feathery surface hoar so it could slide easily and travel far. The surface hoar was reported as being widespread. There may be a melt-freeze crust directly beneath the surface hoar.

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

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • 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

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.

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.