Of all the regions about to get walloped by this storm, the central Columbias is our top contender for weak layers producing large, destructive avalanches. Steer clear of avalanche terrain.
Multiple weak layers present roughly 1 - 2 m deep continue to produce surprising avalanches and will be adjusting to loading on Monday. Avalanches failing on these layers have been large and destructive.
Steady snowfall will form slabs that are increasingly widespread, reactive, and consequential over the day. Expect the danger to be greatest where wind loading is occurring.
The rain line will climb over the day. Steep slopes at elevations receiving wet snowfall or especially rain on previously dry snow will become increasingly unstable.
Large (size 2 to 3) persistent slab avalanches continued on Friday and, to a lesser extent, on Saturday. Remote triggers up to 250 m away figure into some reports.
Our early March layer also produced storm slabs 50 and 80 cm deep in the Selkirks near Revelstoke. The deeper one was a remotely triggered size 2.5 on a north aspect at 1800 m.
There were also many large storm slabs triggered with explosives north of Trout Lake.
24 to 45 cm of new snow should accumulate by end-of day Monday, adding to 60 to 100 cm around Revelstoke and 30 to 50 cm farther south since March 7. It has been redistributed by southwest winds in exposed higher elevation terrain and sits on old wind-affected surfaces at treeline and above or on a crust, which extends up to 1900 m near Highway 1, closer to 2200 m in the south.
Three problem layers of surface hoar, facets and/or crust formed in January and February are in the mid-snowpack, 1 to 2 m deep. They produced numerous destructive avalanches during the weekend warmup and sporadic releases in the days since, making them difficult to rule out, even with factors like a bridging crust at lower elevations.
Sunday Night
Cloudy with flurries bringing 10 to 15 cm of new snow. 30 to 50 km/h southwest ridgetop wind, increasing. Treeline temperature -10 °C.
Monday
Cloudy with steadier snowfall bringing 15 to 30 cm of new snow, greatest in the north. 40 to 60 km/h southwest ridgetop wind, increasing. Treeline temperature to -4 °C by end of day.
Tuesday
Cloudy with increasingly wet snowfall bringing 15 to 30 cm of new snow to higher alpine, rain eventually as high as 2400 m. 50 to 80 km/h southwest ridgetop wind. Treeline temperature reaching 4 °C. with freezing level climbing from 1000 to 2500 m.
Wednesday
Mostly cloudy with wet flurries easing after 10 to 20 cm of alpine snow overnight, rain below about 2300 m. 40 to 60 km/h southwest ridgetop wind, easing. Treeline temperature 2 °C with freezing level between 2300 m and 2600 m.
More details can be found in the Mountain Weather Forecast.
