Avalanche Forecast

Issued: Feb 22nd, 2019 4:48PM

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.

shorton, Avalanche Canada

South Coast.

Human triggered avalanches are likely this weekend. Fresh snow and a buried weak layer have created dangerous avalanche conditions.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

FRIDAY NIGHT: Cloudy with isolated flurries and possible accumulations of 2-5 cm, light to moderate southwest wind, alpine temperatures drop to -4 C.SATURDAY: Scattered flurries with 5-20 cm of snow, light southwest wind, alpine temperatures around -4 C.SUNDAY: Mix of sun and cloud, light southeast wind, alpine high temperatures around -1 C.MONDAY: Sunny, light northeast wind, alpine high temperatures around -1 C.

Avalanche Summary

On 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.Another persistent slab avalanche was reported on Wednesday (see MIN report here), and occurred naturally on a south-facing feature at treeline elevation.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 20 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 50-100 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

A weak layer of facets over a crust is buried approximately 50 cm deep and has been stressed by recent snowfall. Persistent slab problems are unusual for this region.

Stick to non-avalanche terrain or small features with limited consequence.Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.Avoid avalanche terrain during periods of heavy loading from new snow and wind.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Storm Slabs

Fresh storm slabs are possible in steep terrain as 20-30 cm of new snow may be poorly bonded to the snow below.

Avoid avalanche terrain during periods of heavy loading from new snow or wind.Stick to non-avalanche terrain or small features with limited consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Feb 23rd, 2019 2:00PM