New snow and wind are forming deep and reactive slabs. Potential exists for storm slab avalanches to step down to deeply buried weak layers, resulting in very large avalanches. Avoid avalanche terrain and overhead hazard.
A persistent slab problem formed by a crust down 90-200 cm has created a low likelihood, high consequence scenario that is difficult to forecast. Avoid likely trigger spots such as steep, rocky slopes with a shallow or thin to thick snowpack.
New snow and wind are forming fresh, reactive storm slabs. New and recent snow may overlie a weak interface which could result in deeper and touchier than expected storm slabs.
Thursday night: Snowfall starting 10-20 cm. Moderate to strong SW wind. Treeline temperature around -10 °C.
Friday: Snowfall 20-40 cm. Strong SW wind. Treeline high around -4 °C.
Saturday: 10-15 cm overnight then mainly cloudy. Moderate to strong SW wind. Treeline high around -8 °C.
Sunday: A mix of sun and cloud. Moderate W wind. Treeline high around -2 °C.
Evidence of a natural storm slab avalanche cycle size 2-2.5 was observed on NE aspects Wednesday, likely having run during the storm earlier in the week. On Monday and Tuesday, natural storm slabs were reactive to explosive up to size 2 and ski cuts produced storm slabs and loose dry avalanches up to size 1. By Wednesday, explosive results were limited to size 1 loose dry.
On Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This avalanche is detailed in a MIN post and features in our latest blog post, Photos of recent persistent slab avalanches in the southern interior.
20-40 cm of new snow is forecast to fall by the end of Friday. Strong ridgetop winds will likely load new snow into leeward terrain features in the alpine. An accumulated total of 40-70 cm of new and recent snow now sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar in sheltered areas, which may make for a weak bond at this interface.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-200 cm. Activity on this layer has been sporadic, the most recent persistent slab avalanche in the region was on January 2. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.
