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Avalanche Forecast

Archived

Feb 26th, 2019–Feb 27th, 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 possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast.

Persistent slab avalanche problems are tricky to manage and predict. They tend to linger, waiting for a trigger. Check out the Forecasters' BLOG for further details on the conditions in the South Coast region.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Thursday

Weather Forecast

WEDNESDAY: Mostly cloudy. Alpine temperatures near -2 and ridgetop winds light but gusting strong from the East.THURSDAY: Snow 10-15 cm with treeline temperatures near -5 and moderate ridgetop winds from the southwest. Freezing levels near 400 m.FRIDAY: Mix of sun and cloud. Treeline temperatures near -3 and ridgetop winds light from the East.

Avalanche Summary

No recent avalanches reported. I suspect loose dry slufing in steeper terrain features and possibly stiff, isolated wind slabs in open areas in the trees and/ or the alpine. Persistent slab avalanches on the buried crust layer are still a serious concern with conditions not changing in the near future. One occurred naturally on a south-facing feature at treeline elevation on Wednesday (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 snow from the weekend storm sits above a mix of sun crusts and possibly some weak faceted snow and surface hoar. Below this gradually strengthening interface, a widespread crust layer is now buried 50-100 cm deep with weak snow above it. This deeper weak layer has produced large natural and human-triggered avalanches over the past week. A couple of videos from last Wednesday demonstrate how easy it is to trigger this layer. (see 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 saw more snow from recent storms and this storm snow consolidated into a stiffer slab. This problem is not typical for the region and 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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.