Avalanche Forecast
Issued: Jan 16th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Deep Persistent Slabs.
ahanna,
Avalanche Canada
Watch for residual wind slabs that may be sensitive to human triggers. With a high degree of uncertainty around deep layers in a complex snowpack, this may not be the time to dive into ultra committing lines.
Summary
Confidence
Weather Forecast
Saturday night: Flurries, trace, moderate to strong southwest wind, freezing level 800 m.
Sunday: Flurries, trace, moderate northwest wind, freezing level 1000 m.
Monday: Sunny, light northwest ridgetop wind, freezing level 1000 m.
Tuesday: Mix of sun and cloud, southwest ridgetop wind building to strong, freezing level 800 m.
Avalanche Summary
Natural cornice falls up to size 2 have been observed recently. Explosive control work on Friday produced wind slab avalanches up to size 2.
A widespread natural avalanche cycle size 2-3 occurred throughout the region on Wednesday. Avalanche character was predominantly storm slab in the snowy north of the region and wet loose or glide slab in the rainy south. Northwest of Pemberton, several stepped down to buried weak layers resulting in very large (size 3-4) persistent slab avalanches.
Snowpack Summary
- In the south of the region, fluctuating freezing levels during the last storm have resulted in a crust to ridgecrest. At upper elevations, 5-10 cm of dry snow has been blown around by the wind, exposing the crust in some areas and building wind slabs ontop of it in others. This MIN report from Nak Peak on Thursday depicts snow conditions changing with elevation.
- In the north, variable wind effect in the alpine includes scoured windward aspects, sastrugi, hard slab, wind pressed surfaces over lower density snow and isolated pockets of soft snow in sheltered areas. Wind slabs may remain sensitive where they overlie a spotty layer of surface hoar in sheltered terrain or a crust on solar aspects. A widespread surface crust exists below 1600 m.
- A melt-freeze crust from early December is found around 200 cm deep in the snowpack. This crust may have sugary faceted grains sitting above it. This persistent weak layer is most prevalent in the North, northwest of Pemberton where large avalanches have failed on this interface recently. This interface doesn’t seem to be a concern in the South (Coquihalla) and little information is known for the North Cascades or far South in Manning Park.
Terrain and Travel
- Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
- Pay attention to cornices and give them a wide berth when traveling on or below ridges.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
Problems
Wind Slabs
Previous wind has deposited recent snow into deeper slabs on leeward slopes at upper elevations. Wind slabs may remain reactive, particularly where they sit over a spotty layer of surface hoar or a crust on solar aspects.
Cornices have grown large, saggy and fragile.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
A problematic layer consisting of sugary faceted grains over a crust may be found around 200 cm deep. This problem is most predominant along the northwestern border of the region. The likelihood of triggering an avalanche at this interface has reduced, but the consequence of doing so remains high.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 17th, 2021 4:00PM
