Watch for areas where the new snow is drifted into deeper, stiffer slabs. In the north of the region, new snow may test the strength of deeply buried weak layers, and step-down avalanches may be possible.
New snow and strong southwest winds are expected to form fresh wind slabs that are likely to be reactive to human triggering. Expect this problem to be most pronounced in the immediate lee of wind-exposed terrain features. Wind slab releases currently carry a serious risk of triggering a deeper weak layer, especially in shallow, rocky areas in the northern part of the region.
A problematic weak layer is buried 30-70 cm deep in the snowpack in the north of the region. New snow and wind will add additional load to this fundamentally unstable snowpack structure. This problem is largely absent in the south of the region.
Monday night: Cloudy with isolated flurries with 1-3 cm of accumulation, moderate southwest winds, alpine temperatures around -3 C, with freezing levels around 800 m.
Tuesday: Cloudy, 10-20 cm of snow, moderate to strong southwest winds, alpine high temperatures around -2 C, with freezing levels around 1400 m.
Wednesday: Cloudy, 20-30 cm of snow, moderate southwest winds, alpine high temperatures near 0 C with freezing levels around 1400 m.
Thursday: Partly cloudy, isolated flurries with trace accumulations, light variable winds, alpine high temperatures around -7 C.
The likelihood of triggering avalanches increases with the incoming storm.
Avalanche activity has diminished since the widespread avalanche cycle a week ago, and no recent activity has been reported. During that cycle, avalanches were reported to be running to valley-bottom in the north of the region and failing on deeply buried weak layers. See this MIN report of an avalanche involvement from last week for an example of this avalanche problem.
The possibility for large human-triggered persistent slab avalanches remains a concern at higher elevations in the northern part of the region (e.g., Duffey, Hurley, etc.), especially as newly formed wind slabs create the potential for smaller avalanches to step-down to these layers.
The storm brings new snow for strong southwest winds to drift into touchy wind slabs in exposed areas near and above tree line.
The snowpack below varies significantly between the northern and southern parts of the region. In the north (e.g. Duffey, Hurley) 5-15 cm of snow from the weekend has been drifted onto leeward features at upper elevations. Elsewhere this recent snow remains unconsolidated or was warmed as product of solar radiation and warm air temperatures. The interface below it may present as surface hoar in many sheltered locations.
The upper snowpack consists of around 30-70 cm of snow that overlies a weak layer from late November composed of sugary faceted grains and hard melt-freeze crust. This presents a persistent slab problem that may persist for weeks to months with the potential to produce large and destructive avalanches. This persistent weak layer is largely absent in the south of the region.
