Avalanche Forecast
Issued: Dec 4th, 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.
dsaly,
Avalanche Canada
Pay attention if the wind picks up - reactive slabs may form quickly over weak surface hoar. Choose conservative terrain and consider that hazard may be highest at treeline elevations.
Summary
Confidence
Low
Avalanche Summary
A weak layer of surface hoar below recent snow has been responsible for recent snowpack instability. Reports suggest this interface is most prevalent at treeline, between 1700-2000 m, but reported as low as 1450 m.
Wednesday: a natural avalanche cycle size 2-3 was reported in both the Selkirks and Monashees north of Revelstoke. Whumpfing and cracking were reported throughout the region.
Thursday and Friday: Widespread reports of whumpfs and cracks continued, and included a size 2 avalanche remote triggered by skiers in the Selkirks south of Revelstoke.
Saturday: a reactive snowpack continued to be reported throughout the region on Saturday. From Blue River to Kokanee glacier skiers reported whumpfs and cracking. In the Monashees near Revelstoke, shooting cracks were reported as low as 1450 m.
As well on Saturday, 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.
Snowpack Summary
Low-density flurries have dusted localized areas overnight and cold temperatures and starry skies are promoting surface hoar growth and facetting.
Buried 40-70 cm, a layer of surface hoar, crust, and faceted crystals is the persistent layer of concern. This layer has been most reactive between 1700-2200 m, but reported as low as 1450 m with widespread whumpfing and cracking reported around the region. Cold temperatures and little wind have limited slab development over this layer, this could quickly change as 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
Sunday night
Clear with patchy cloud, possible inversion and valley fog forming. Northeast wind 10-25 km/hr. Treeline temperature low -22 °C
Monday
Increasing cloud and isolated flurries, trace accumulation. Southwest wind 10-20 km/hr. Treeline high temperature -16 C.
TuesdayIncreasing cloud and isolated flurries, trace to 5 mm accumulation, high snow-to-liquid ratios could produce enhanced snowfall at upper elevations. West wind 15-25 km/hr. Treeline high temperature -12 C.
WednesdayCloudy, windy, and flurries, up to 10 mm accumulation forecast (cold, low-density snow). Southwest wind gusting upwards of 40 km/hr. Treeline temperature rising to -8 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.
- Keep in mind that human triggering potential persists as natural avalanching tapers off.
- Carefully monitor the bond between the new snow and old surface.
Problems
Persistent Slabs
A layer of surface hoar and crust is found 40-70 cm deep in the snowpack. Limited slab properties have developed, yet recent whumpfing and cracking suggest this layer is primed for human triggers. 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
Wind has redistributed snow in localized areas at upper elevations. There's a lot of loose snow out there, expect fresh slabs to form where the wind picks up.
Aspects: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Dec 5th, 2022 4:00PM
