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Avalanche Forecast

Archived

Feb 16th, 2021–Feb 17th, 2021

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

Regions

Northwest Coastal.

Moderate to strong northwest wind overnight will form fresh wind slabs where soft snow is available for transport. Warmer temperatures might consolidate the snow above the late January persistent weak layer and develop into slabs that can be triggered by skiers and riders.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

TUESDAY NIGHT: Cloudy with clear periods, trace of new snow, moderate to strong northwest wind, temperature low -10 C.

WEDNESDAY: Mix of sun and cloud, light to moderate northwest wind, temperature high -4 C.

THURSDAY: Cloudy, 5 cm of new snow, strong southerly wind, temperature high -6 C.

FRIDAY: Cloudy, 15-25 cm of new snow, moderate southwest wind, temperature high -4 C.

Avalanche Summary

Natural wind slabs to size 2 have been reported on various wind loaded and cross loaded aspects over the weekend. These wind slabs were formed by the recent outflow winds. Wind slabs have also been reactive to human triggering with ski cuts in the size 1-1.5 range.

On Saturday explosives control triggered cornice and wind slabs, mostly size 1-2 with the odd larger result with big cornices.

It is worth remembering that skiers were able to trigger unsupported pillows failing on surface hoar down 25-40 cm near Terrace last week. Although there are no recent reports of avalanches failing on this layer, it is still propagating in some snowpack tests.

Snowpack Summary

The recent 10 cm of new snow sit on top of a variety of older snow surfaces. Recent cold temperatures encouraged surface faceting of the upper snowpack. Hard slabs, scoured slopes and sastrugi are present underneath the new snow where outflow effects were the strongest. Below treeline, 10-30 cm of snow sits above isolated pockets of surface hoar and a crust which is more prominent on solar aspects. The late January interface is down 30-70 cm and consists of surface hoar in sheltered locations, a crust on solar aspects, and facets and stiff wind affected snow at upper elevations. 

The mid-pack seems to be well settled. Deep persistent layers appear to have mostly become unreactive, except for the Bear Pass area and the far reaches south of Kitimat. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.