The snowpack is not to be trusted. Reports of large, human-triggered avalanches on a buried weak layer continue across aspects and elevations. Keep it conservative on Saturday. Where more than 20 cm of snow accumulates, expect avalanche danger to be HIGH.
A weak layer of surface hoar sits 35-70 cm deep, and human-triggering is likely. Over the past several days, large human, machine, and remotely-triggered avalanches have released on this layer. Avalanche activity is expected to become more likely and widespread, as more areas approach critical loading with the incoming snow.
Snowfall amounts are expected to vary across the region. Areas that accumulate more than 20 cm may develop a widespread storm slab problem. In areas where less snow accumulates, slab formation will be specific to where the wind transports snow into deeper drifts.
Weak snow at the bottom of the snowpack continues to pose a deep persistent slab avalanche problem. Treat wind-scoured, rocky, shallow terrain as suspect and avoid big alpine slopes that are threatened by cornices overhead.
Friday night: Cloudy, 5-10 cm snow, light south wind, alpine temperature -4 C.
Saturday: Cloudy, 5-15 cm new snow, light southwest wind, alpine high temperature -4 C, freezing level 1000 m.
Sunday: Mostly cloudy, scattered flurries with up 5 cm of snow, light southwest winds, alpine high temperature -5 C, freezing level 1000 m.
Monday: Mostly clear, light southwest wind, alpine high temperature -4 C, freezing level 1200 m.
Over the past week, large (size 2-2.5) persistent slab avalanches have been observed where the most snow has accumulated over a layer of surface hoar. Human, machine, and remotely-triggered avalanches have all been reported, even as professionals tiptoe around and avoid suspect terrain features. The problem is touchy but tricky. In many instances, slopes were ski cut with no results, only to have the third or fourth skier in the group accidentally trigger the slab.
Over the past several days, small to large (size 1-2) natural, human-triggered, and explosive-triggered avalanches have been observed breaking in the recent storm snow. A few large (size 2) cornices were also observed failing naturally. With incoming snow overnight, a new touchy storm slab problem may form on the surface, increasing the potential for cornices to reach their breaking point and creating conditions where shallow avalanches have the potential to step-down to deeper layers.
On Thursday, professionals reported large (size 2.5) explosive triggered avalanches releasing on weak layers near the ground. These avalanches occurred on north and east facing slopes above 2300 m, and they confirm that this problem remains a concern.
An incoming storm is expected to bring up to 20+ cm of snow to the region by afternoon on Saturday. Snowfall amounts are expected to vary across the region. Areas that accumulate more than 20 cm may develop a touchy storm slab problem.
A weak layer of surface hoar sits 35-70 cm deep. It may sit over a crust on solar aspects. With snow in the forecast, more areas are expected to reach critical loading and slab formation over this layer. The problem will likely become more reactive and widespread. Read more about surface hoar on our forecaster blog!
Deep basal facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.
