Avalanche Forecast
Regions: Boundary, Howson, Kitimat, Microwave-Sinclair, Nass, Northwest Coastal, Rupert, Seven Sisters, Shames, Stewart.
There's cause for concern in the south as accumulations on weak layers catch up with the north, where persistent slabs are already active. Manage uncertainty with low consequence terrain.
Confidence
Moderate
Avalanche Summary
A MIN report from the Shames area on Wednesday describes wind slab formation and reactivity to skier traffic that helped confirm active conditions near Terrace.
Simultaneous remote-triggered size 2.5 and size 2 persistent slabs were seen Thursday, triggered from 150 m away. They fit a pattern of increasing persistent slab activity up north, where natural avalanches up to size 3 failing on the early December crust have been focused around northwest aspects in the alpine.
Snowpack Summary
Up to 60 cm of recent snow overlies previously wind affected surfaces in the alpine and at treeline. Roughly half this amount accumulated on Wednesday through Thursday and has fed into new wind slab development. You'll likely find moist surface snow or thin accumulations on crust below 900 m.
Below these surface layers, two distinct weak layers exist in the top meter of the snowpack. A layer of facets and/or surface hoar down 30 to 50 cm and the early December crust down 50 to 90 cm. Recent observations of these layers in the Terrace area are limited. They are a pronounced problem in the north.
Treeline snow depth range from 200-280 cm. The lower snowpack has no layers of concern.
Weather Summary
Friday Night
Cloudy with continuing flurries bringing a trace to 5 cm of new snow. 10 to 25 km/h south ridgetop wind, easing. Freezing level falling from 800 m to 500 m.
Saturday
Mainly cloudy with isolated flurries. 5 to 15 km/h east ridgetop wind. Freezing level to surface with treeline temperature falling to -5 °C.
Sunday
Mainly sunny. Calm to 5 km/h variable ridgetop wind. Treeline high temperature around -4 °C
Monday
A mix of sun and cloud. 5 to 10 km/h variable ridgetop wind. Treeline high temperature -5 °C.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
- Start with conservative terrain and watch for signs of instability.
- Be aware of the potential for large avalanches due to buried weak layers.
- Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.
Avalanche Problems
Wind Slabs
Recent steady snowfall and elevated winds have been forming fresh wind slabs in open, leeward terrain.
Surface avalanches may have potential to step down to weak layers in the top metre of the snowpack.
Aspects: North, North East, East, West, North West.
Elevations: All elevations.
Likelihood: Possible - Likely
Expected Size: 1 - 2
Persistent Slabs
Steady snowfall has been incrementally bringing a critical load to the early December crust, which is already a serious problem in the north of the region. Slabs failing on this interface have been large and destructive.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1.5 - 2.5