We have uncertainty around the reactivity of a buried weak layer that produced large rider-triggered avalanches last weekend. Read our latest blog for advice on how to manage a persistent slab problem.
As ridgetop winds pick up today from the northwest, any loose surface snow will be transported into fresh wind slabs in atypical terrain features due to reverse-loading.
Aging wind slabs formed by previous southwest wind may remain reactive to human triggers, especially where they overlie a weak, sugary lower snowpack.
A buried weak layer composed of surface hoar and facets has produced surprising skier-triggered avalanches in the past week. Avalanches are most likely to be triggered on this layer in areas around treeline.
In the past week, we've had multiple reports of persistent slab avalanches on a buried weak layer. On the weekend, two skier-triggered size 2 avalanches were reported ~40 cm deep at treeline near Golden. Otherwise, persistent slab avalanches throughout the region have been mostly explosive controlled, size 1-2.
In the neighboring central Columbia and west Kootenay regions, where it is buried deeper, this layer has produced several alarming rider-triggered avalanches. Unfortunately, more likely than not, this is a sign of what is to come for the Purcells.
Variable surfaces range from hard old wind slabs at wind exposed elevations to soft, unconsolidated facets in sheltered areas.
A concerning weak layer composed of surface hoar, facets and/or a crust that formed in mid November is now buried 15-40 cm deep. Avalanche activity has been observed on this layer and is expected to continue as the overlying snow takes on more slab character due to settlement, wind and additional snow load.
Alpine snowpack distribution is variable, with depths ranging from 40 to 140 cm.
Thursday night
Increasing cloud. Light northwest wind. Alpine low -13 C.
Friday
A mix of sun and cloud. Moderate northwest ridgetop wind. Alpine high of -10 C.
Saturday
Scattered flurries bringing a trace of snow. Light to moderate northwest wind. Alpine high of -12 C.
Sunday
Scattered flurries bringing a trace of snow. Light to moderate southwest wind. Alpine high of -20 C.
More details can be found in the Mountain Weather Forecast.
