Intense snowfall, strong wind, and warm temperatures are creating dangerous avalanche conditions that warrant wide terrain margins. Avoid avalanche terrain and overhead exposure on Saturday.
The combination of rapid snowfall, strong winds, and warm temperatures is packing a powerful punch that has potential to wake up deeper layers buried in the snowpack. Touchy storm slab avalanches could step down to these persistent weak layers resulting in a very large avalanches 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.
Friday night: Cloudy, 20-30 cm of snow, transitioning to rain below about 1800 m, strong southwest winds, alpine temperatures approaching 0 C as freezing levels may reach 2000 m overnight.
Saturday: Cloudy, 15-25 cm of snow, strong southwest winds shifting northwest and easing, alpine temperatures dropping to about -7 C as freezing levels fall from 1900 m to valley bottom over the day.
Sunday: Mix of sun and cloud, isolated flurries with a trace of new snow, light southwest winds, alpine high temperatures around -8 C.
Monday: Mix of sun and cloud, isolated flurries with a trace of new snow, light northwest winds, alpine high temperatures around -10 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, on all aspects, at all elevations. They have been triggered by humans, explosives, and naturally.
There were two notable natural avalanches reported in the Selkirks on Thursday. These were very large (size 3.5-4) persistent slab avalanches breaking 100-250 cm deep on both southeast and northwest slopes above 2400 m. These avalanches add to the previous two observations of very large persistent slab avalanches over the past week. These avalanches indicate that a deeper instability may become reactive with additional loading. Touchy storm slab avalanches or cornice fall have the potential to step-down to this layer.
20-35 cm of snow fell at higher elevations on Friday. By Saturday afternoon, an additional 35-50 cm is expected to accumulate. 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 m overnight, triggering wet loose avalanches. The hazard from wet loose avalanches will decrease as temperatures cool throughout the day on Saturday.
The mid and lower snowpack is generally well settled and strong, however, there is a weak layer of surface hoar currently buried 90 to 170 cm deep. This layer has recently shown signs of instability in the north of the region. New snow, rain, and warming will collectively add considerable strain to this weak layer. The potential for this persistent slab problem to fail naturally and produce large, destructive avalanches will increase during the storm.
