Avalanche Forecast
Issued: Dec 7th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
trettie,
Avalanche Canada
Conditions are more complicated than what meets the eye. Fresh wind slabs formed at upper elevations. Riders may be drawn to more sheltered areas around treeline to avoid these wind slabs, but should consider that this is where the persistent slab problem has been most problematic to date. Keep your terrain choices conservative and don't let good riding lure you into more hazardous terrain.
Summary
Confidence
Moderate
Avalanche Summary
On Tuesday a few size 1 to 2 wind slab avalanches were reported in the region . These avalanches were in treeline and alpine terrain on northerly aspects.
A weak layer of surface hoar below recent snow has been responsible for the latest snowpack instability. Reports suggest this interface is most prevalent at treeline, between 1700-2000 m, but it was also reported as low as 1450 m.
Sunday: Skier triggered and natural avalanches up to size 2 were reported around treeline on easterly aspects in the south of the forecasting region. They failed on feathery surface hoar about 40 cm deep. In the Revelstoke area, skiers triggered avalanches up to size 2.5 about 40-70 cm deep (see a picture in this MIN report and a more detailed description of the same avalanche in this MIN report). Avalanches were triggered on southerly and north aspects at treeline and in the lower alpine and some were triggered from a short distance away.
Snowpack Summary
Up to 35cm low-density snow fell on a cold snow surface consisting of feathery surface hoar on shaded aspects and a sun crust on sun exposed aspects. This new snow will likely be redistributed by incoming southerly winds.
Buried 40-80 cm deep, a layer of surface hoar, crust, and faceted crystals is the persistent layer of concern. This layer has been most reactive at treeline between 1700-2200 m, but it was also observed as low as 1450 m and widespread whumpfing and cracking was reported throughout the region.
Snowpack depths range from 70 cm at treeline to 170 cm in the alpine, with wind-loaded areas exceeding 200 cm.
Weather Summary
Wednesday Night
Flurries bringing a trace of new snow. Moderate southwest winds with a low of -14 at 1800m.
Thursday
Cloudy with 5 to 10cm of new snow expected. Moderate to strong winds with a high of -10 at 1800m.
Friday
Mostly cloudy with another 5cm of new snow expected. Light southwest winds with a high of -10 at 1800m.
Saturday
Mostly cloudy with flurries bringing trace amounts of new snow. Light to moderate southerly winds with a high of -8 at 1800m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
- Expect slab conditions to change drastically as you move into wind exposed terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Persistent Slabs
A layer of surface hoar and crust is found 40-80 cm deep in the snowpack. Skiers triggered avalanches up to size 2 on this layer on Sunday. Whumpfing and cracking was reported throughout the region. Reports indicate this layer of surface hoar is most prevalent between 1700-2000 m, but it was also observed as low as 1450 m.
Be cautious when entering wind affected terrain. With a weak layer of surface hoar below, fresh wind slabs may be more widespread, extend into treeline elevations, and be more reactive than expected in sheltered areas.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Incoming southerly winds are likely to redistribute new snow into wind slabs on East, north and west aspects.
The wind might have formed slabs at treeline elevations where a buried persistent weak layer exists. Fresh wind slabs above this layer might be more reactive and result in larger avalanches than expected.
Aspects: North, North East, East, South East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 8th, 2022 4:00PM
