Avalanche Forecast

Issued: Feb 17th, 2021 4:00PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

Avalanche Canada ldreier, Avalanche Canada

Strong to extreme southwest wind is in the forecast. The wind will distribute the 5-10 cm new snow falling throughout the day and form fresh reactive wind slabs in lee terrain features in the alpine and at treeline.

Summary

Confidence

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

Weather Forecast

WEDNESDAY NIGHT: Increasing cloud coverage, 2 cm of new snow, south wind increasing from light to extreme, temperature low -9 C, freezing level at valley bottom.

THURSDAY: Cloudy, 5-10 cm of new snow and 20 cm in the very south of the region around Kitimat, strong to extreme southwest wind, temperature high -3 C, freezing level at 700 m.

FRIDAY: Cloudy, 20-25 cm of new snow, strong southwest wind, temperature high -4 C, freezing level at 700 m.

SATURDAY: Cloudy, 15-20 cm of new snow, strong to extreme southwest wind, temperature high -4 C, freezing level at 800 m.

Avalanche Summary

Several dry loose avalanches up to size 2.5 on steep terrain were reported on Tuesday. 

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

10-20 cm of recent snow sits on top of a variety of older snow surfaces consisting of facets and crust, hard wind slabs, scoured slopes and sastrugi. Below treeline, 10-30 cm of soft 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

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • 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

An icon showing Wind Slabs

The wind is forecast to shift to southwest overnight and increase to extreme. It will form fresh wind slabs in the alpine and at treeline throughout the day where soft snow is available for transport. In the very south of the region where around 20 cm new snow is expected the fresh wind slabs will form faster and larger. 

Recent shifting winds have created wind slabs on multiple aspects and all elevations. Older wind slabs may still be triggered by humans, especially where they sit on a weak faceted crystal layer. Wind slabs might also be present in open terrain pockets at treeline and below treeline.

The strong to extreme southwest winds will contribute to cornice growth.

Aspects: North, North East, East, South East, West, North West.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

30-70 cm of snow sits above a buried weak interface that consists of surface hoar, facets and/or a crust. As the snow above this layer becomes more consolidated, the likelihood of avalanches may increase. Triggered wind slabs may step down to this layer and failing cornices may trigger avalanches on this layer.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Valid until: Feb 18th, 2021 4:00PM