Dramatic warming has contributed to a steady pattern of destructive persistent slab activity and Sunday promises more. It'll be a great day to soak up the heat in low-consequence terrain.
Weak layers exist below the most recent storm snow and up to about 90 cm deep. They will be likely to produce avalanches throughout the warmup. Small avalanches may also step down.
High freezing levels and solar warming will work to destabilize snow on steep slopes sheltered from the wind. Moist or wet snow may shed naturally or with a human trigger and loose releases may trigger more destructive slab avalanches.
Explosives control in Ymir Bowl produced a size 3 persistent slab on a steep, northwest-facing feature at 2100 m on Friday. It's consistent with a pattern of recent persistent slabs in the size 2 to 3.5 range, mainly running on the late January crust and featuring 60 - 80 cm crowns. See the size 3.5 below. Heightened persistent slab activity will be concern for the duration of the warmup.
Many wet loose and wet slabs were also controlled or ran naturally in Kootenay Pass Friday.
A melt-freeze crust or moist snow likely makes up the surface on all but high elevation north aspects. High overnight freezing levels mean crust recovery may be weak. This crust tops the upper part of 30 to 50 cm of settling recent snow, which is wind affected at higher elevations and may overlie faceted snow or surface hoar where sheltered.
Two other key weak layers are present in the mid snowpack: a surface hoar or thin crust from mid-February buried 40-60 cm deep, and faceted snow/surface hoar/crust from late January buried 60-90 cm deep. These layers have been active during recent storms and warm temperatures and remain in question while warming continues to test the snowpack.
Saturday Night
Clear. 5 to 15 km/h south ridgetop wind. Freezing level falling from 3100 m to 2600 m.
Sunday
Mainly sunny with cloud increasing in the afternoon. 5 to 20 km/h variable ridgetop wind, shifting northwest and increasing. Freezing level falling to 2400 m. Treeline temperature 6 °C.
Monday
Partly cloudy with scattered flurries increasing. 20 to 30 km/h north ridgetop wind. Freezing level to 1700 m. Treeline temperature around 0 °C.
Tuesday
Partly cloudy with 5 - 10 cm of new snow above 1700 m from overnight flurries.
More details can be found in the Mountain Weather Forecast.
