Reactive wind slabs may exist at treeline and in the alpine.Approach ridgelines with caution, and begin with a conservative route plan. Cracking and whumpfing are signs of instability.
Fresh and reactive wind slabs exist at upper elevations. Human triggering is more of a concern on north through east slopes in the alpine, especially where they sit above buried surface hoar.
Looming cornices exist and may become more fragile during a wind event or with solar radiation. They can act as a large enough trigger to initiate slab avalanches from the slopes below.
On Wednesday, two human-triggered slab avalanches (size 2 and a size 3) were reported in the Selkirks. These were on north through northeast slopes at 2400 m. These may have failed on a buried surface hoar layer down 30 to 70 cm. The size 2 was a remote trigger from 20 away.
A few natural storm slabs were seen up to size 2 and wet loose up to size 3.
On Friday, reactive wind slabs at treeline and above are likely on north through east aspects.
15 to 35 cm of recent storm snow exists at treeline and above with high northeast facing slopes seeing deeper accumulations due to wind transport. Moist snow exists up to 2200 m on polar aspects and to ridgetop on solars.
Below the recent storm snow (2300 m and above) is a buried surface hoar layer from early April. This has been reactive to human triggering on high north through east-facing slopes. A buried melt-freeze crust also exists and extends to the ridgetop on solar aspects and near 2400 m on polar aspects.
The late March rain crust is now down 80 to 100 cm. This buried crust is capping a moist upper snowpack.
Weak layers buried in early March, February and January are now down anywhere from 150 cm to 250 cm.
Thursday Night
Mainly cloudy with snow 5 to 15 cm. 25 to 60 km/h southwest ridgetop wind. Treeline temperature -7 °C. Freezing level falling to 1300 m.
Friday
Cloudy with sunny periods and isolated flurries. 15 to 25 km/h southwest ridgetop wind. Treeline temperature -5 °C. Freezing level 1700 m.
Saturday
Cloudy with sunny periods and flurries up to 10 cm. 20 to 40 km/h west ridgetop wind. Treeline temperature -6 °C. Freezing level 1500 m.
Sunday
Mix of sun and cloud. 10 gusting to 40 km/h northwest ridgetop wind. Treeline temperature -8 °C. Freezing level 1900 m.
More details can be found in the Mountain Weather Forecast.
