Avalanche Forecast
Issued: Dec 5th, 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.
ldreier,
Avalanche Canada
Strong northwest wind will form reactive wind slabs overnight Monday to Tuesday and during the day Tuesday. Choose conservative terrain and consider that hazard may be highest at treeline elevations where the new snow sits on weak surface hoar and where a persistent weak layer is buried 40-70 cm deep.
Summary
Confidence
Avalanche Summary
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.
Thursday and Friday: Widespread reports of whumpfs and cracks, and a size 2 avalanche was remote triggered by skiers in the Selkirks south of Revelstoke.
Saturday: Reports of a reactive snowpack continued throughout the region. From Blue River to Kokanee Glacier, skiers reported whumpfing and cracking. In the Monashees near Revelstoke, shooting cracks were reported as low as 1450 m. Explosives triggered numerous size 2 avalanches failing 50-60 cm down on surface hoar. These avalanches were triggered between 2000-2100 m on north to west aspects.
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
Low-density snow will fall on a cold snow surface with feathery surface hoar and sugary facets covered by a dusting of low-density snow.
Buried 40-70 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 around the region. Cold temperatures and little wind have limited slab development over this layer, this will quickly change when the wind increases with plenty of low-density snow available for transport.
Snowpack depths range from 70 cm at treeline to 150 cm in the alpine, with wind-loaded areas exceeding 200 cm.
Weather Summary
Monday night
Cloudy and up to 10 cm low-density snow forecast. Northwest wind 40-60 km/h at higher elevations in the alpine and potentially at treeline and southwest wind 20 km/h at lower elevations. Treeline temperature low -16 °C.
Tuesday
Cloudy and 10-20 cm low-density snow forecast. Northwest wind 40-60 km/h at higher elevations in the alpine and potentially at treeline and southwest wind 20 km/h at lower elevations. Treeline high temperature -12 °C.
WednesdayMostly cloudy and flurries, up to 10 cm low-density snow forecast. Westerly wind 20-30 km/h. Treeline temperature rising to -8 °C.
ThursdayCloudy, up to 5 cm new snow. Southwest wind increasing to 50 km/h. Treeline temperature rising to -7 °C.
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 40-70 cm deep in the snowpack. Skiers triggered avalanches up to size 2 on this layer. And widespread whumpfing and cracking was observed over the last several days. Reports indicate this layer of surface hoar is most prevalent between 1700-2000 m, but reported as low as 1450 m.
Keep an eye on the wind, slabs may quickly form wherever the fresh snow is encouraged to bond; and with a weak layer of surface hoar below, 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
Strong northwest wind is forecast at upper elevations. It is uncertain how strong the wind will be at treeline elevations. There is a lot of loose snow out there, and new low-density snow will add to the snow available for transport. Keep an eye on the wind. Expect fresh slabs to form quickly where the wind picks up.
If the wind forms wind slabs at treeline elevations where a buried persistent weak layer exists, triggered wind slabs might step down and result in larger avalanches than expected.
Aspects: North East, East, South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 6th, 2022 4:00PM
