Avalanche Forecast

Brrrrrr! Cold and dry conditions persist under arctic air

Wednesday night: Mostly clear, light northeast ridgetop wind, alpine temperature -23 C.

Thursday: Sunny, light northeast ridgetop wind, alpine high temperature -24 C.

Friday: Sunny, light northeast ridgetop wind, alpine high temperature -18 C.

Saturday: Increasing cloud, light southeast ridgetop wind, alpine high temperature -15 C. 

Since Monday, there have been numerous reports of natural and human-triggered wind slabs. Several were solar-triggered by cornice falls. These avalanches released on north through east through southeast aspects above 2000 m and broke 25 cm deep. In this MIN from London Ridge, observers reported a very large wind slab avalanche that may have stepped down to a deeper layer. 

Reports of human-triggered avalanches breaking on the late January surface hoar continue to trickle in. Check out this MIN report from Tuesday that shows a small (size 1.5) skier-triggered persistent slab avalanche in the RMR backcountry. These avalanches have been primarily in the near treeline elevation band. However, this MIN report and this MIN report from over the weekend are helpful examples of how cutblocks or "treeline-like" features that are below treeline have caught groups off-guard. 

Numerous small (size 1-1.5) loose dry avalanches in unconsolidated snow have been reported in steep terrain.

Up to 45 cm of low density snow over the weekend has combined with moderate winds primarily from the northwest to create wind slabs which may remain reactive in lee features. In sheltered areas, cohesion-less powder may be prone to dry loose avalanches that can run far and fast in these cold, dry conditions. With clear skies, steep slopes in direct sun may rapidly warm midday despite the cold temperatures, which may weaken cornices and promote instability.

80-130 cm of snow from the past week is settling over a weak layer of surface hoar that has shown reactivity at treeline or in "treeline-like" features below treeline. This persistent weak layer has potential to surprise backcountry users with how wide the fracture can travel across slopes. This layer will be slow to gain strength and requires careful terrain selection.

A less reactive layer of surface hoar or facets buried in early January can be found down 100-160 cm.

The mid/lower snowpack is generally well settled and strong in most areas.

• Carefully evaluate steep lines for wind slabs.
• Cornice failure may trigger large avalanches.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.