Avalanche Forecast
Issued: Dec 26th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
ahanna,
Avalanche Canada
Bits of new snow are keeping wind slabs fresh and will be especially sensitive to seeing the sun for the first time.
We're being patient and sticking to conservative terrain for the next while until we have clear evidence that buried weak layers have stabilized.
Summary
Confidence
Weather Forecast
Saturday night: A trace of new snow, moderate southwest wind, freezing level valley bottom.
Sunday: Clearing, light northwest wind, alpine temperature -8 C, freezing level 500 m.
Monday: Sunny, light northwest wind, alpine temperature -9 C, freezing level valley bottom.
Tuesday: Sunny, light northwest wind, alpine temperature -11 C, freezing level valley bottom.
Avalanche Summary
Many storm and persistent slab avalanches have been observed this week across the region. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and between 2000 and 2300 m. The most recent was a size 1 on Saturday near Nelson, triggered by a skier on a cross-loaded slope around treeline. Although avalanche activity is becoming smaller and more sporadic, the potential to trigger buried weak layers remains.
Snowpack Summary
5-10 cm of new snow may sit over surface hoar. Below, 30-40 cm of wind affected snow from the previous storm is taking some time to bond with underlying snow.
Two weak layers are buried around 50 to 100 cm deep. The layers are composed of feathery surface hoar and sugary faceted grains and they overly a hard melt-freeze crust. There has already been substantial avalanche activity on this layer from natural and human triggers. This layer remains a major concern, as humans may be able to trigger large and destructive avalanches on it. There has been less avalanche activity reported west of Castlegar but a similar snowpack exists so the possibility remains.
Another crust with associated faceted grains may be found near the base of the snowpack. There haven't been recent avalanches reported on this layer but it remains on our radar. The most likely place to trigger it would be from shallow, rocky terrain.
Terrain and Travel
- Be carefull around freshly wind loaded features.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Uncertainty is best managed through conservative terrain choices at this time.
- Avoid being on or under sun exposed slopes.
Problems
Persistent Slabs
Weak layers of surface hoar and/or faceted grains overly a hard melt-freeze crust around 50 to 100 cm deep. Loading from recent storms have pushed the persistent slab problem over the tipping point resulting in large avalanches in the past week. We're being patient and sticking to conservative terrain for the next while until we have clear evidence that buried weak layers have stabilized.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Small inputs of recent snow with overnight wind is keeping the windslab problem fresh. Fresh slabs will be especially sensitive when touched by the sun for the first time.
Older wind slabs are taking time to bond to underlying snow and may be found on a variety of aspects due to previous wind from various directions.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 27th, 2020 4:00PM
