Avalanche Forecast
Issued: Feb 16th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
ldreier,
Avalanche Canada
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.
Summary
Confidence
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
The forecast calls for moderate to strong northwest wind overnight which will form fresh wind slabs on lee terrain features where soft snow is available for transport. Wind slabs will be especially susceptible to human triggering where stiff and punchy feeling snow sits on top of weak faceted crystals.
The wind varied in direction over the last week. The shifting winds have created wind slabs on multiple aspects and all elevations. Older wind slabs might also be present in open terrain pockets at treeline and below treeline. Cold temperatures preserved the weak bond between the slabs and the weak faceted crystal layer underneath. These wind slabs may still be triggered by humans and propagate wider than expected.
Aspects: North, North East, East, South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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
Expected Size
Valid until: Feb 17th, 2021 4:00PM
