Human triggered avalanches are likely this weekend. Fresh snow and a buried weak layer have created dangerous avalanche conditions.
Summary
Confidence
Moderate -
Weather Forecast
SATURDAY NIGHT: Clear periods, light east wind, alpine temperatures drop to -5 C.SUNDAY: Mix of sun and cloud in the morning and clearing in the afternoon, light northeast wind, alpine high temperatures around -2 C.MONDAY: Sunny, light northeast wind, alpine high temperatures around -4 C.TUESDAY: Sunny, moderate northeast wind, alpine high temperatures around -6 C.
Avalanche Summary
On Friday, several small human triggered slabs were reported in the top 10-15 cm of new snow. Loose dry sluffing was observed in steep terrain.Persistent slab avalanches on the buried crust layer are still a serious concern. One occurred naturally on a south-facing feature at treeline elevation on Wendesday
(see MIN report here). Last Monday, search and rescue responded to an avalanche in the Mount Seymour backcountry, which resulted in a fatality
(see here for incident report). The avalanche occurred on a steep feature at treeline elevation. Avalanche professionals involved in the rescue indicated wide propagation consistent with a persistent slab problem. The crown depth was variable - 40 to 100 cm, indicating there was also wind loading in that area. A widespread avalanche cycle occurred a week ago. These large avalanches (up to size 2.5) showed impressive propagation, with some being triggered remotely (from a distance) and in some occasions stepping down to the crust and releasing persistent slab avalanches.
Snowpack Summary
Roughly 30 cm of new snow sits above a mix of sun crusts and possibly some weak faceted snow and surface hoar. A widespread crust layer is buried 50-80 cm deep with weak snow above it that has produced large natural and human-triggered avalanche over the past week. These videos from Wednesday clearly demonstrate how easy it is to trigger this weak layer (
here and
here). The reactivity of this layer appears to be worse in the south of the region (i.e. the North Shore Mountains) since this part of the region has seen more snow and it has consolidated into more of a slab. Unusually for this region, we expect this layer to remain reactive for some time into the future. The lower snowpack is settled and strong.
shorton,
Avalanche Canada
