Avalanche Forecast

Issued: Feb 18th, 2021 4:00PM

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

Avalanche Canada ldreier, Avalanche Canada

20-30 cm new snow by the end of the day on Friday combined with strong southwest wind will increase the avalanche danger quickly throughout the day. The storm and wind slabs will be most reactive where they sit on cold facets, surface hoar and hard wind affected surfaces.

Summary

Confidence

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

Weather Forecast

THURSDAY NIGHT: Cloudy, 10-15 cm new snow and up to 30 cm in the very south of the region, strong southwest wind, temperature low -5 C.

FRIDAY: Cloudy, 10-15 cm new snow, strong southwest wind, temperature high -3 C, freezing level at 700 m.

SATURDAY: Cloudy, 15-20 cm new snow, strong to extreme southwest wind, temperature high 0 C, freezing level rising to 900 m.

SUNDAY: Cloudy, 25-35 cm new snow, strong southwest wind, temperature high +1 C, freezing level at 1000 m.

Avalanche Summary

Whumpfing was reported by a party on Wednesday (see this MIN report). Many natural wind slab avalanches of size 2-2.5 were observed on lee terrain features and cross-loaded slopes. Several small dry and wet loose avalanches were reported on steep solar aspects. 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 and this layer might become reactive with the increasing snow load.

Snowpack Summary

20-40 cm of recent snow sit on top of a variety of older snow surfaces consisting of facets and crust, hard wind slabs, scoured slopes and sastrugi. Below treeline, 20-50 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 40-80 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 changing conditions today, storm slabs may become increasingly reactive.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • 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

Storm Slabs

An icon showing Storm Slabs

On Thursday fell 10 cm new snow throughout the region. In some colder areas as for example around Bear Pass and Rosswood fell 20-30 cm low density snow. Overnight 10-15 cm snow are expected and another 10-15 cm are in the forecast during the day on Friday. Storm slabs will form throughout the day and become increasingly reactive, especially where they sit on cold facets, surface hoar or hard wind affected surfaces. 

Strong southwest wind will continue to form wind slabs in the alpine and at treeline. In areas with strong wind and intense snow fall slabs will form faster and be reactive sooner in the day.

The strong southwest winds will promote cornice growth.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

An icon showing Persistent Slabs

40-80 cm of snow sits above a buried weak interface that consists of surface hoar, facets and/or a crust. And more snow is in the forecast. As the load on this layer increases and the snow becomes more consolidated with warmer temperatures, the likelihood of avalanches may increase. Triggered wind and storm slabs may step down to this layer and failing cornices may trigger avalanches on this layer.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Feb 19th, 2021 4:00PM