Avalanche Forecast

Moderate - Forecast precipitation (either snow or rain) amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Heavy snowfall and extreme wind on Saturday

Friday night: Overcast, 10-20 cm of snow, moderate southeast winds becoming strong southwest in the alpine, treeline temperatures rising from -8 C to -6 C.

Saturday: Overcast, 20-40 cm of snow above 600 m, strong southwest winds with extreme gusts, treeline temperatures rising to near -4 C in the afternoon, freezing level rising to 600 m.

Sunday: Decreasing cloudiness, up to 5 cm of snow overnight, light northeast winds, high treeline temperatures near -8 C, freezing level around 400 m.

Monday: Mix of sun and cloud, no snow expected, light west winds, high treeline temperatures near -7 C, freezing level at valley bottom. 

Natural avalanches releasing in the new snow are likely on Saturday. These storm slab avalanches are expected to be large, widespread, and very sensitive to human-triggers. Avalanches in the new snow have the potential to step-down to recently reactive weak layers, producing very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below. 

On Thursday, we received reports of two large (size 2-3) avalanches that released on a persistent weak layer on northwest and southwest aspects between 1700-1900 m. There are valuable photos and accounts in this MIN report and this MIN report. Notably, skiers remote-triggered these avalanches while traveling uphill. Several small (size 1-1.5) sympathetic avalanches also released on nearby terrain features during these close calls. Operators also reported a small (size 1.5) explosive-triggered persistent slab on a steep north aspect at 1900 m. 

 

An intense storm is taking aim at the region, with 30-60 cm of new snow expected by Saturday afternoon. The new snow is falling on a mix of previous snow surfaces, including wind-scoured surfaces, wind-drifted snow, and preserved powder. Although storm slabs are expected to be widespread across aspects and elevations, extreme southwest winds will be a major contributor to the size and likelihood of Saturday's storm slab problem. 

A primary layer of concern is a weak layer of facets (sugary snow) over a widespread crust that formed in early December (down 100-180 cm). On Thursday, this persistent slab problem surprised several recreationists with large, remotely-triggered avalanches. Additionally, backcountry travelers continue to report whumphing on this layer. See this MIN report from the Chuting Gallery on Thursday. This problem is particularly hard to predict, tricky to manage, and will likely continue to surprise complacent backcountry travelers. Given recent remote-triggered and sympathetic avalanche activity, these conditions require wide, conservative terrain margins and disciplined backcountry travel techniques. Get more details and photos in our forecaster blog. 

• Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
• Avoid the runout zones of avalanche paths. Avalanches could run full path.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
• Cornice failures could trigger very large and destructive avalanches.