Watch for new wind slab formation on Sunday as new storm snow accumulates. Older wind slabs may also still be reactive to human-triggers.
Watch for new wind slab formation on Sunday as new snow accumulates with moderate southwest wind.
Lingering old wind slabs from the recent northeast wind may still be reactive to human-triggering in exposed high elevation terrain. These would be most likely where they overlie a weak layer from mid-February or in steep, unsupported terrain features.
The first in a series of relatively weak storm systems is forecast to reach the region on Sunday morning.
Saturday Night: Increasing cloud cover, light to moderate SW wind, treeline low around -10 °C.
Sunday: Light snowfall 4-8 cm, moderate SW wind, treeline high around -4 °C.
Sunday night and Monday: Light snowfall 10-15 cm, moderate SW wind, treeline high around -1 °C.
Monday night and Tuesday: Mainly light snowfall, moderate to strong SW wind, freezing levels reaching around 2000 m.
On Friday, a size 1 wind slab was remotely triggered from 3 m away on a north aspect in the alpine which was 10 cm thick. A size 1.5 wind slab was reported which was triggered on a south aspect and was 20 cm thick. Explosives triggered a couple cornices which triggered wind slabs on the slopes below. One other small avalanche was triggered on a sheltered roll at treeline which failed on the mid-February surface hoar.
On Thursday, a few natural wind slabs up to size 2.5 were observed in the alpine in the western part of the region. Explosive use triggered several size 2-2.5 cornice releases. One of these cornices releases triggered a small slab on the slope below.
The new snow will bury a highly variable snow surface which includes wind-affected surface in exposed terrain, a thin sun crust on solar aspects which may be faceting, surface hoar in sheltered areas, and/or old storm snow which may be faceting on shaded slopes.
A weak interface from mid-February was down around 20-40 cm prior to the storm. It consists of a sun crust on solar aspects, facets, and/or surface hoar. This layer was previously only reactive in wind-loaded terrain where a slab had formed but it is expected to become a more widespread problem as the storm progresses and builds a more widespread slab.
A layer of buried surface hoar from late-January sits 30-60 cm deep in the snowpack and is most likely to be found on north aspects in sheltered areas. Though there haven't been reports of recent avalanches on this layer in this region, it is still on the radar of many operations and could potentially wake up during the storm.
