Avalanche Forecast
Regions: Boundary, East Stikine, Howson, Kitimat, Nass, Ningunsaw, Northwest Coastal, Rupert, Seven Sisters, Shames, Stewart, West Stikine.
Adopt a cautious approach.
A problematic weak layer is surprising riders and producing large avalanches.
Remote triggering is a concern, avoid exposure to steep overhead slopes.
Confidence
High
Avalanche Summary
In recent days, large to very large (size 2-4) natural and human-triggered persistent slab avalanches have been reported, including several notable incidents on Tuesday. These avalanches have exhibited unexpectedly wide propagation, with some remote triggers occurring from distances of up to a kilometer away.
Notably, on the 28th this sobering near miss surprised riders, and this MIN describes skiers triggering large avalanches from valley bottom.
Snowpack Summary
The alpine has seen extensive recent wind-affect. Moderate to strong southeast winds are forecast overnight and into Thursday, and may build fresh wind slabs.
The primary layer of concern is a persistent weak layer of surface hoar and facets overlying a crust. It is buried 50 to 100 cm in the southern parts of the region, and is buried deeper, up to 200 cm, in some areas north of Stewart. This layer has been cause of several recent large avalanches with wide propagation. Looking forward, we expect this layer to remain a concern for many days, or even weeks.
The remainder of the snowpack is well settled, with no current layers of concern. Treeline snow depths are around 160 cm.
Weather Summary
Wednesday night
Clear. 25 km/h east ridgetop winds. Treeline temperature -15 °C.
Thursday
Clear, with increasing cloud in the afternoon. 25 to 40 km/h southeast ridgetop wind. Treeline temperature -10 °C.
Friday
A mix of sun and cloud. 25 to 30 km/h southeast ridgetop wind. Inversion: treeline temperature -10 °C.
Saturday
Mostly sunny. 15 to 30 km/h south ridgetop wind. Inversion: Treeline temperature -10 °C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Be aware of the potential for large avalanches due to buried weak layers.
- Remote triggering is a concern; avoid terrain where triggering overhead slopes is possible.
- Use conservative route selection and resist venturing into complex terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Avalanche Problems
Persistent Slabs
Recent large avalanches have failed on weak grains over a buried crust. This weak layer has shown wide propagation across large terrain features.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1.5 - 3
Wind Slabs
Use caution as you enter wind-affected terrain.
Aspects: North, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 1 - 2