Avalanche Forecast
Issued: Jan 6th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
MBender,
Avalanche Canada
New snow has continued to accumulate over the past several days. This has gradually increased the load sitting above buried persistent weak layers. Persistent slab avalanches are best managed by choosing conservative terrain.
Summary
Confidence
Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.
Weather Forecast
Wednesday Night: Flurries, 5-10 cm, light southwest wind, alpine high -4.
Thursday: Mainly cloudy, light south wind, alpine high -4, freezing level 800 m.
Friday: Mainly cloudy with sunny breaks, moderate south wind, alpine high -3, freezing level 900 m.
Saturday: Flurries, moderate southwest wind, alpine high -5, freezing level 700 m.
Avalanche Summary
On Tuesday there was a report of a naturally triggered size 2.5-3 wind slab avalanche which stepped down mid-path to the early December persistent weak layer. This was on an east aspect near ridgetop and occurred in the central part of the region. As well there were reports of several explosives controlled size 2 storm snow avalanches in Kootenay Pass on southerly aspects between 1800 and 2100 m.
A remotely triggered (from a distance) size 2 persistent slab avalanche was reported near Rossland on Sunday. The details can be seen in MIN posts here and here.
Numerous natural, human and explosive triggered storm slabs size 1-2.5 were reported on Saturday and Sunday. Check out this avalanche triggered remotely by a skier in Kootenay Pass on the weekend.
Sporadic reports of persistent slab avalanches have been popping up, including a natural size 3 near Whitewater on Sunday. With new snow slowly but steadily piling up, the chances of a resurgence of persistent slab avalanches will increase. This incremental loading makes it difficult to predict when the tipping point will be reached. The uncertainty around this problem is best managed with conservative terrain selection.
Snowpack Summary
40-70 cm of recent storm snow accumulating over the past week has seen wind affect at upper elevations. In sheltered areas, the recent snow may sit over surface hoar.
Two weak layers are buried in close proximity to one another. They are 70-100 cm deep around Nelson and 50-80 cm deep around Rossland and other western parts of the region. The layers are composed of feathery surface hoar and sugary faceted grains and they overlie a hard melt-freeze crust.Â
Terrain and Travel
- Continue to make conservative terrain choices while the storm snow settles and stabilizes.
- Be especially cautious as you transition into wind affected terrain.
- Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Storm Slabs
Storm slabs may remain sensitive to human triggers, especially in freshly wind loaded features at upper elevations and where recent snow sits over surface hoar in wind sheltered areas.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
Weak surface hoar and/or faceted grains sit above a melt-freeze crust 70 to 100 cm deep. This layer is being stressed as new snow slowly but steadily piles up. This incremental loading makes it difficult to predict when the tipping point will be reached. We are currently seeing only sporadic avalanches running on these layers, but they have been large. The uncertainty around this problem is best managed with conservative terrain selection.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 7th, 2021 4:00PM
