New slabs are expected to form with today's storm. Be cautious in terrain features around ridges, as well as elsewhere if enough snow accumulates.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
SATURDAY NIGHT: Cloudy with snowfall, accumulation 10 to 15 cm, strong southwest winds, freezing level rising to 1000 m.SUNDAY: Cloudy with light snowfall, accumulation 10 to 15 cm, moderate southwest winds, alpine temperature -6 C, freezing level 1000 m.MONDAY: Clearing over the day, light south winds, alpine temperature -8 C, freezing level 800 m.TUESDAY: A mix of sun and cloud, light northwest winds, alpine temperature -8 C, freezing level 500 m.
Avalanche Summary
Many avalanches were triggered from explosives on Friday. Most of the avalanches were small to large (size 1 to 2) and released in the recent snow, 30 to 100 cm deep. There was further evidence of a natural cycle that ran during the storm on Thursday.Numerous larger avalanches (size 2 to 3) were observed as well, with slabs around 200 cm thick. These likely released on a weak layer near the base of the snowpack, as described in the snowpack discussion.
Snowpack Summary
New slabs will form during the storm on Saturday night and Sunday. Below around 1800 m, expect new snow to fall onto a melt-freeze crust formed by rain from Thursday’s storm.A weak layer of facets and surface hoar lies below storm snow (over 3 m in the past two weeks!). Recent avalanche activity is mostly running in the storm snow above this layer but there have been reports of avalanche stepping down deeper within the snowpack, possibly to this weak layer.At the base of the snowpack, weak and sugary facets exist below an early-season melt-freeze crust. This weak layer has been the culprit for sporadic, very large avalanches in alpine terrain in the past few weeks. The avalanches have occurred in areas where the ground roughness is very smooth, for example glaciers, firn, and shale/rock slab slopes. An avalanche could be triggered in this layer in areas with smooth ground roughness either where the snowpack is thin or with a very large trigger such as a cornice fall. Storm slab avalanches could also step down to this layer.
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.