Intense snowfall, strong wind, and warming temperatures are creating dangerous avalanche conditions that warrant wide terrain margins. Avoid avalanche terrain and overhead exposure on Saturday.
Ongoing snowfall will continue to build touchy storm slabs at higher elevations. Forecast strong winds and warm temperatures will speed up slab formation as new snow accumulates as well as contribute to rapid cornice growth. Natural avalanches are likely, and overhead hazard is a significant concern on Saturday.
Wet loose avalanches will continue to be a concern on Saturday at lower elevations that see rain instead of snow accumulating. This problem is expected to decrease in likelihood as the freezing levels drops throughout the day.
Rapid snowfall, ongoing wind transport, and warm temperatures will test the weak snow buried at the bottom of the snowpack. Triggering deep persistent slab avalanches is most likely in snowpack areas that transition from thick to thin, like in shallow, rocky start zones. Touchy storm slab avalanches could step down to this deeper layer, resulting in a very large avalanches on Saturday.
Friday: Cloudy, 10-20 cm snow transitioning to rain below about 1900 meters, moderate to strong southwest winds, alpine temperatures reaching +1 C as freezing levels climb to 2100 meters.
Saturday: Cloudy, 10-20 cm of snow, rain below about 1800 meters, moderate southwest winds, becoming strong at ridge-top, alpine temperatures around 0 C with freezing levels beginning to fall from 2000 meters in the afternoon.
Sunday: Mostly clear, light southwest winds, alpine high temperatures around -8 C, freezing level at valley bottom.
Monday: Partly cloudy, light northwest winds, alpine high temperatures -9 C.
Due to continuous stormy weather, there have been daily avalanches reported in the region. Most of these have been storm and wind slab avalanches, up to size 3 but mostly around size 1-2. They have been triggered by humans, explosives, and naturally. These have occurred on all aspects, mainly at treeline and alpine elevations.
Over the past week, there have been several deep persistent slab avalanches reported in the region. Two were triggered by explosives and one that occurred near Golden was remotely triggered by humans. This activity outlines the fact that this layer remains a problem in the region. Large alpine features, especially rocky, thin snowpack areas are the most likely places to trigger this layer. Touchy storm slab avalanches may have the potential to step-down to this layer. Reports also indicate that cornices may be reaching their breaking point and may act as triggers for larger avalanches.
Over the past 2 days, 20-30 cm has fallen at higher elevations. By Saturday afternoon, an additional 20-35 cm is expected to accumulate above 1900 m. Forecast strong winds and warm temperatures will speed up slab formation as new snow accumulates as well as contribute to rapid cornice growth. A large, natural avalanche cycle is expected. Rain is forecast to saturate snow surfaces up to 1900 meters, triggering wet loose avalanches. The hazard from wet loose avalanches will decrease as temperatures cool throughout the day on Saturday.
A weak layer of surface hoar can currently be found about 70 cm deep around Golden and Kimberley, 30 cm deep around Invermere, and 100 cm deep along Kootenay Lake.
As usual for the Purcells, the base of the snowpack contains basal facets and it remains possible to trigger these deep weak layers in shallow rocky start zones or from a heavy trigger such as a cornice fall or explosives. New snow, rain, and warming will collectively add considerable strain to these weak layers. Their potential to fail naturally and produce large, destructive avalanches will be significantly increased during the storm.
