Avalanche Forecast

Arctic air pushes south into the interior, mixing with a low pressure system off the coast of Vancouver. Temperatures will steadily drop but expect a daily refresh of low density snow through to Boxing Day.

FRIDAY NIGHT: Up to 5cm overnight. Moderate southerly winds. Alpine low of -15.

SATURDAY: Cloudy with light snowfall, 2-5cm over the day and another 5-10cm overnight. The southern half of this region will see 

predominantly light to moderate winds from the south-east, and areas further north will experience gusty northeasterly winds as the Arctic air pushes through. Alpine high of -15. 

SUNDAY: Light snowfall over the day, up to 5cm expected. Light easterly winds. Alpine highs of -20.

MONDAY: Clearing skies with increasing westerly winds. Alpine high of -20.

Yesterdays snowfall produced a natural cycle was observed to size 3 in steep treeline and alpine terrain. Human triggered slabs were also observed to size 1 in wind loaded features.

A notable size 1 remote wind slab was remotely triggered on a north aspect below treeline. Riders felt a settlement while in the runout, and this triggered the slab on a steep piece of terrain on an adjacent slope. While this avalanche was small, it does indicate the reactivity of the persistent weak layers in the lower snowpack and the potential for fractures to travel over a distance. This avalanche problem is challenging to forecast and is best managed by conservative terrain management. 

Explosive control work throughout the North Columbia's and nearby Glacier National Park produced slab avalanches size 2-3. 

If head into the mountains, please submit your findings and photos through a Mountain Information Network report.

Up to 40cm of fresh storm snow has accumulated this week. In the alpine and exposed treeline elevations it has been redistributed into deeper deposits in wind loaded features by southwest winds.

At lower elevations the settling storm snow may sit over a weak surface hoar layer, which is creating slabs that are reactive to human triggers. The surface hoar is most likely to be found on sheltered slopes at treeline and below.

The crust formed by the early December rain event sits 100-150cm deep and is found up to 2200m in the North Columbia's. In most terrain the snow above is well bonded to the crust. In areas where the crust is buried deeper than one meter, it has begun to decompose and shows limited reactivity.

However in some areas, weak faceted grains have been observed above - creating a weak interface that is still reactive to human triggers. This is most common at treeline elevations where the crust is thinner. 

• Continue to make conservative terrain choices while the storm snow settles and stabilizes.
• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.