Human-triggered persistent slab avalanches are still possible in the alpine and treeline where a thick crust does not exist.
Surface hoar and facets in the upper snowpack have recently produced large avalanches. These layers are mostly likely to be reactive at upper elevations where no surface crust has formed.
As temperatures rise, the surface snow may become moist and unstable on solar slopes, producing small loose wet avalanches.
At treeline and above, a few wet loose avalanches were seen from steep terrain features. Where a thick, supportive surface crust is found, we expect that triggering avalanches on buried weak layers is unlikely.
A natural avalanche cycle continued through last week, with very large slab avalanches (to size 4) failing on buried persistent weak layers. Skiers were able to remotely trigger large slides.
A melt-freeze crust has formed on most surfaces. Dry snow persists on northerly aspects at upper elevations.
Three persistent weak layers remain notable in the snowpack and have been responsible for recent large avalanches. Surface hoar that formed in mid-March can be found 50 to 100 cm below the snow surface. Below this, another layer of surface hoar that formed in early March can be found at a depth of 100 to 150 cm. Additionally, a layer of facets, surface hoar, and/or a crust from mid-February is buried 100 to 200 cm deep.
Monday Night
Clear periods. 10 to 25 km/h west ridgetop wind. Treeline temperature -3 °C. Freezing level 400 m.
Tuesday
Mix of sun and cloud with isolated flurries. 15 to 30 km/h northwest ridgetop wind. Treeline temperature -1 °C. Freezing level 1200 m.
Wednesday
Mix of sun and cloud. 15 to 30 km/h northwest ridgetop wind. Treeline temperature -1 °C. Freezing level 1300 m.
Thursday
Mix of sun and cloud. 10 to 25 km/h west ridgetop wind. Treeline temperature 3 °C. Freezing level 1700 m.
More details can be found in the Mountain Weather Forecast.
