Avalanche Forecast
Regions: Kootenay Boundary.
An increasing trend of large persistent slab avalanches is a growing concern in the region. Choose terrain with the expectation that a smaller storm slab could trigger a deeper weak layer in the snowpack.
Confidence
Moderate - Forecast snowfall amounts are uncertain.
Weather Forecast
Wednesday night: Cloudy with increasing flurries bringing 10-15 cm of new snow. Moderate to strong southeast winds.
Thursday: Cloudy with continuing flurries bringing 10-20 cm of new snow. Moderate to strong south winds easing over the day. Alpine temperatures around -8.
Friday: Broken cloud cover. Light southwest winds. Alpine temperatures around -11.
Saturday: Cloudy with scattered flurries bringing about 5 cm of new snow. Light to moderate south winds. Alpine high temperatures around -7.
Avalanche Summary
This region has been a hot spot for recent avalanche activity. A number of large natural avalanches up to size 3 were reported on east, southeast and south facing slopes above 2000 m in the Rossland area Monday with crowns up to 100-150 cm in depth.
In the rest of the region both natural and explosive controlled avalanches up to size 2.5 were observed on all aspects above 1800 m. Many avalanches failed on the December 27th Surface Hoar and one avalanche on a north/northeast facing slope at 1800 m involved the mid November facets.
On Sunday the bulk of the avalanche activity was limited to loose dry avalanches but a spooky avalanche was remote triggered by a group of skiers, more details and photos in this MIN report.
Snowpack Summary
The storm of the last several days brought 20 to 50 cm of snow which fell with moderate to strong southwest wind before winds switched to the north/northeast Sunday night.Â
The resulting wind fueled storm slabs likely remain sensitive to human triggers, particularly in exposed lee terrain features. More recent snow might hide slabs and make it trickier to navigate around them.
Deeper in the snowpack, a few layers of weak and feathery surface hoar may still be found around 70 to 130 cm deep which have been active as recently as Monday.
The base of the snowpack is also weak in parts of the region where it consists of sugary faceted snow around a melt-freeze crust.
Terrain and Travel
- Avoid freshly wind loaded terrain features.
- Storm slab size and sensitivity to triggering will likely increase through the day.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
Avalanche Problems
Storm Slabs
Another 20-35 cm of new snow may accumulate in the region by the end of Thursday, adding to 20 to 50 cm from Sunday into Monday and bringing us to 80 to 180 cm in the last week! Uncertainty exists around which recent storm interfaces may remain active, but fresh storm slabs and newly buried wind slabs are likely candidates.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Very Likely
Expected Size: 1 - 2
Persistent Slabs
Several persistent weak layers are buried in the snowpack. It is possible for humans to trigger them, or for storm or wind slab avalanches to step down to them and form very large avalanches. Recent avalanche observations on deeply buried weak layers are on an increasing trend in our region.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible - Likely
Expected Size: 2 - 3