Avalanche Forecast

Issued: Feb 23rd, 2019 4:04PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Persistent Slabs and Storm Slabs.

Avalanche Canada shorton, Avalanche Canada

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.

Problems

Persistent Slabs

An icon showing Persistent Slabs
A weak layer of facets over a crust is buried 50-80 cm deep and has been stressed by recent snowfall. Persistent slab problems are unusual for this region.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Use conservative route selection, choose moderate angled and supported terrain with low consequence.Avoid open slopes with any steepness over 30 degrees.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3

Storm Slabs

An icon showing Storm Slabs
Fresh storm slabs are possible in steep terrain as 30 cm of new snow may be poorly bonded to the snow below.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Avoid open slopes with any steepness over 30 degrees.Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2

Valid until: Feb 24th, 2019 2:00PM

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