Avalanche danger will increase as touchy storm slabs build through the day Sunday.
As storm slabs build through the day Sunday, 10-30 cm of new snow overlies surface facets, surface hoar and sun crusts. Recent avalanche activity indicates a poor bond between these old surfaces and the new snow. Storm slabs will be deepest in lee terrain features near ridges, as the snow is falling with strong southwest wind.
In the north of the region (e.g. Duffey, Hurley, Goldbridge), a buried weak layer lingers at the base of the snowpack. The most likely place to trigger this layer is in shallow and rocky terrain. We doubt that the new loads from the present storm will be sufficient to induce pervasive avalanche activity on these layers, but as is typical with deep persistent avalanche problems, there is uncertainty.
Saturday night: Flurries bringing a trace of new snow. Light to moderate southwest wind. Freezing level 1000 m.
Sunday: 10-25 cm new snow with lightest accumulations in the Duffey. Strong southwest wind. Freezing level 1000 m.
Monday: Overnight snowfall up to 10 cm of new snow in most areas and 20 cm for the Coquihalla. Mix of sun and cloud. Light to moderate northwest wind. Freezing level 700 m.
Tuesday: Mix of sun and cloud. Light to moderate southwest wind. Freezing level 1300 m.
Natural storm slab and loose dry avalanches to size 1.5 were observed in the Duffey on Saturday.
10-25 cm of new snow will fall through the day Sunday. Forecast strong southwest winds are expected to redistribute the new snow at alpine and treeline elevations, loading lee terrain features. 20-30 cm of recent snow now sits over a layer of widespread surface facets, surface hoar in sheltered areas or sun crusts on solar aspects. Storm slabs are expected to slide easily on these weak layers.
In the north part of the region (e.g. Duffey/Hurley/Goldbridge), a deep instability exists in the snowpack, consisting of a weak basal facet-crust complex. Sporadic avalanche activity on this layer is keeping it on our radar, with the latest report described here. In the south of the region, including the Coquihalla and Manning areas, there are no concerns about deeply buried weak layers.
