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Avalanche Forecast

Archived

Feb 24th, 2019–Feb 25th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast.

Conservative terrain choices are critical. Although the chance of triggering large avalanches is decreasing, the consequences of doing so are high.

Confidence

Moderate -

Weather Forecast

SUNDAY NIGHT: Clear, moderate northeast wind, alpine temperatures drop to -5 C.MONDAY: Sunny, light to moderate northeast wind, alpine high temperatures around -3 C.TUESDAY: Sunny, moderate northeast wind, alpine high temperatures around -6 C.WEDNESDAY: Sunny with cloudy periods, strong northeast wind, alpine high temperatures around -3 C.

Avalanche Summary

Several small (size 1) human triggered slabs were reported in the storm snow on Saturday and Friday. Loose dry sluffing was also 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, a fatal avalanche occurred on a steep feature at treeline elevation in the Mount Seymour backcountry (see here for incident report). 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.

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 50-100 cm deep with weak snow above it that has produced large natural and human-triggered avalanche over the past week. These videos from Wednesday 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

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.