Avalanche Forecast

High.

FRIDAY NIGHT: Mostly cloudy, freezing level below valley bottom. SATURDAY: Cloudy with light snowfall, accumulation 5 to 10cm, moderate southwest winds, alpine temperature -6°c, freezing level below valley bottom. SUNDAY: Cloudy with snowfall, accumulation 10 to 20cm, moderate southwest winds, alpine temperature -6°c, freezing level 1000m. MONDAY: Clearing over the day, light south winds, alpine temperature -8°c, freezing level 800m.

Many avalanches were triggered from skiers and explosives on Thursday. Most of the avalanches were small to large (size 1 to 2) and released in the recent storm snow, 30 to 100 cm deep. Earlier in the week, three very large avalanches (size 2.5 to 3.5) were triggered with slabs around 100 to 200 cm thick and likely released on a weak layer near the base of the snowpack, as described in the snowpack discussion.

Thursday's storm dumped 30 to 50 cm of snow, with extreme winds (gusts to 180 km/h). All terrain features near ridges could have touchy slabs due to variable wind directions. Below around 1800 m, expect to find a melt-freeze crust formed by rain from Thursday's storm. New snow on Saturday will fall on these surfaces. A weak layer of facets and surface hoar lies below all this 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.