Light new snow amounts and wind have formed fresh wind slabs at higher elevations. In the north of the region, this adds a layer of complexity to a serious persistent slab problem. Danger in the south of the region is MODERATE and specific to wind slab concerns.
Persistent slabs may not be a concern in the south of the region, but a cautious snowpack evaluation is still warranted at higher elevations where the 5-15 cm of new snow has been redistributed into wind slabs on leeward features near ridgetop.
A problematic weak layer is buried 30-70 cm deep in the snowpack in the north of the region. This layer has recently produced large and destructive avalanches that have travelled far. This problem is largely absent in the south of the region.
Saturday night: Cloudy, light southwest winds, alpine temperatures around -5 C, with freezing level near 1100 m.
Sunday: Mostly cloudy, isolated flurries with a trace of accumulation, light southwest winds, alpine high temperatures near 0 C and freezing level rising to 1600 m.
Monday: Mix of sun and cloud, light to moderate southwest winds, alpine high temperatures around -3 C, with freezing level around 800 m.
Tuesday: Cloudy, 8-12 cm of snow expected during the day and overnight, moderate to strong southwest winds, alpine high temperatures around -1 C, with freezing level rising to 1200 m.
Avalanche observations have been on a declining trend since the widespread avalanche cycle last weekend, although we have few recent reports to draw from. During that cycle, avalanches were reported to be running to valley-bottom in the north of the region, failing on deeply buried weak layers. See this MIN report of an avalanche involvement from last weekend for an example of this avalanche problem.
The possibility for large human-triggered persistent slab avalanches remains a serious concern at higher elevations in the northern half of the region (e.g., Duffey, Hurley, etc.), especially as more sensitive wind slabs create the potential for small avalanches to step-down to these layers. These persistent weak layers continue to produce concerning snowpack test results and are expected to heal slowly.
5-15 cm of new snow has fallen on a weak interface with moderate southwest winds forming shallow, reactive wind slabs on leeward features at upper elevations. Higher snow amounts and stronger, more sustained winds have occurred in the northern part of the region.
Below the surface, the storm at the end of last week brought over 120 cm of snow to the south of the region and about 40 cm to the north of the region. This snow is gaining strength, but conditions beneath this layer vary dramatically and, in some areas, are highly problematic.
In the north of the region, the above-mentioned storm snow brought a critical load to a 30-70 cm-deep weak layer from late November, composed of sugary faceted grains and hard melt-freeze crust. This structure is a recipe for large and destructive avalanches, and it presents a problem that may persist for weeks to months. This persistent weak layer is largely absent in the south of the region.
