Use extra caution around large slopes and thin areas at treeline. There is uncertainty in how the mid January surface hoar layer will respond to the incoming weather.
The incoming storm will likely form new wind slabs that will not bond well to the crust that covers much of the terrain. Strong winds could mean that wind slab could be found further down slope then expected.
It's possible to trigger avalanches on a 30-50 cm deep surface hoar layer that has recently been reactive near Terrace and Stewart. Most avalanche activity has been at treeline elevations, but we are still uncertain about the spatial distribution of this problem.
Thursday night: freezing level will fall to 500m with moderate to strong south winds in the alpine. Light snow starting around midnight.
FRIDAY: Storm arrives with cloudy skies and up to 10mm of precipitation. Moderate to strong wind from the south, freezing level fluctuates between 500 m and 1000 m.
SATURDAY: Stormy weather continues with another 15cm of snow, strong wind from the south, freezing level fluctuates between 500 m and 1000 m.
Sunday: some light flurries with light to moderate southwest winds. High of -2 at 900m.
Warm sunny weather earlier this week has resulted in a few loose wet and glide slab avalanches. The most concerning avalanche activity has been a string of persistent slab avalanches over the past week. These have occurred on a 30-50 cm deep layer of surface hoar in southern parts of the region around Terrace and Stewart. This has included both natural avalanches and human-triggered avalanches. The photos of the avalanche in this MIN report at Clague are good examples of the type of treeline elevation terrain where this problem can be found. We are uncertain whether the persistent slab problem will remain reactive after the melt freeze cycle tapers off.
As the storm arrives early Friday morning new wind slab and storm slabs could develop over old refrozen surfaces.
The snow surface has recently undergone a spring-like melt-refreeze pattern. The snowpack is likely capped by a hard crust in most areas except high north facing terrain. Below this is a surface hoar layer burried 30 to 50cm deep and could still be triggered at treeline in the Terrace and Stewart areas.
