Avalanche Forecast
Issued: Dec 6th, 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
Westerly wind formed fresh wind slabs in the alpine and at treeline. Choose conservative terrain and consider that hazard may be highest at treeline elevations, where fresh slabs may sit on a 40-80 cm deep persistent weak layer.
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.
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.
Monday: No new avalanches were observed. However, whumpfing and cracking was reported at treeline and below in the Monashees.
Snowpack Summary
Up to 20 cm 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.
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. In wind exposed areas, the loose snow formed reactive wind slabs over this layer.
Snowpack depths range from 70 cm at treeline to 170 cm in the alpine, with wind-loaded areas exceeding 200 cm.
Weather Summary
Tuesday night
Cloudy with up to 10 cm low-density snow. West wind 30 km/h. Treeline temperature low -12 °C.
Wednesday
Cloudy with a trace of new snow. West wind changing to southwest 25 km/h. Treeline temperature rising to -9 °C.
ThursdayCloudy, up to 5 cm new snow. Southwest wind increasing to 50 km/h. Treeline temperature rising to -6 °C.
FridayMostly cloudy, up to 5 cm new snow. Southwest wind 30 km/h. Treeline high temperature -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 40-80 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
Westerly wind formed fresh wind slabs in the alpine and at treeline. Be cautious as you transition into wind affected terrain.
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, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 7th, 2022 4:00PM
