Wind slabs will continue to develop over the day. Watch for fresh loading as slabs will remain reactive to human triggers. Recent northerly winds may have loaded unexpected features in terrain further north. Keep your guard up as you move into exposed terrain at all elevations.
Storm snow has been redistributed by winds from the north and south into deeper, reactive slabs in wind loaded features on all aspects especially as you move north in the region. Take care when moving through wind affected terrain at all elevations. Expect fresh slabs to keep building over the day as moderate southwest winds continue.
A layer of weak facets (sugary snow) can be found down 80-150 cm near a crust layer that formed in early December. Although this persistent weak layer hasn't recently shown reactivity in this area, it is possible to trigger avalanches on this layer, especially at treeline elevations.
The best strategy with a persistent avalanche problem is conservative terrain management - avoid likely trigger spots such as steep convex slopes, and areas where the snowpack tapers rapidly from thick to thin. Learn more about this problem here in a recent forecaster blog.
Arctic air continues to push south, keeping the Columbia's well below seasonal temperatures. An active low pressure system approaches on Wednesday night.
SUNDAY NIGHT: A chance of flurries overnight. Light westerly winds.
MONDAY: Partly cloudy with moderate westerly winds. Isolated flurries. Alpine high of -20.
TUESDAY: Partly cloudy with isolated flurries. Alpine high of -22. Moderate westerly winds.
WEDNESDAY: Isolated flurries, alpine high of -22. Strong westerly winds.
The heavy snowfall this week produced a natural slab cycle to size 3 throughout the region on Wednesday and Thursday. 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.
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. In the southern parts of the region, winds have been consistent from the southwest. In the north, southwest winds came in with the snow and were followed by a northerly blast, redistributing snow into unusual loading patterns found on all aspects.
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.
