Kootenay Boundary

Although a cooling trend means the snowpack is gaining strength, persistent slabs remain a concern for riders. Use caution anywhere the snowpack is thin or variable.

FRIDAY NIGHT: Cloudy, no precipitation, moderate southwest wind, treeline and alpine temperatures around -3 C with freezing level around 1000 m.

SATURDAY: Cloudy with isolated flurries, up to 5 cm of new snow, moderate to strong west wind, treeline temperatures around -5 C with freezing level around 1000 m.

SUNDAY: Cloudy skies, no precipitation, strong westerly wind, treeline temperatures around -4 C, possible temperature inversion with alpine temperatures of -1, freezing level around 1000 m.

MONDAY: Flurries up to 5 cm, moderate to strong westerly wind, treeline temperatures around -5 C, possible temperature inversion with alpine temperatures of -1, freezing level around 1000 m.

Thursday, large avalanches with impressive propagation were triggered by strong solar radiation and warm temperatures (+5 C at treeline). Several loose wet avalanches were also observed at lower elevations along with significant pinwheeling. While in motion, some of these loose avalanches pulled large storm slabs, scouring avalanche paths to the ground in places.

A widespread avalanche cycle occurred during Wednesday's warm storm. This included numerous sizes 1-2 avalanches and one size 3 avalanche on Ymir Mountain. These avalanches were 20-40 cm thick, and in many cases were suspected to have failed on a recently buried surface hoar layer (see photos in the MIN post). 

We have not heard reports of persistent slab avalanches since last weekend when we saw numerous sizes 2 to 3 avalanches releasing on the early December facet/crust layer. Prior to these avalanches, we were seeing a regular pattern of large destructive avalanches on this layer at the start of the month. These avalanches mostly occurred on thin, wind-affected slopes near ridge tops. 

A breakable crust is now capping the dense 10-30 cm recent snow which is continuing to settle with the mild temperatures. This crust seems thinner on north and east slopes but present up to 1900 m. Below it, a layer of feathery surface hoar and melt-freeze crusts are found. Lower elevations have gone through a melt-freeze cycle. An accumulated total of 70-100 cm of snow since the beginning of January sits over variable and potentially weak snow surfaces, including widespread facets and/or surface hoar up to 5 mm in sheltered areas.

The early December crust/facet layer has been responsible for sporadic but very large, persistent slab avalanches over the past month. The crust is now buried 120-200 cm deep except in thin, wind-affected areas near ridgetops where most of the recent avalanches have been triggered.

• Keep in mind that human triggering potential persists as natural avalanching tapers off.
• Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.