Avalanche Forecast

Issued: Feb 26th, 2019 4:58PM

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

swerner, Avalanche Canada

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.

Summary

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

A weak layer of facets over a crust is buried 50-100 cm deep. Triggering large avalanches on this layer remains possible in steep terrain.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Minimize exposure to sun exposed slopes when the solar radiation is strong.Be aware of the potential for wide propagations due to the presence of a buried weak layer.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

2 - 3

Loose Dry

Loose dry avalanches may be running in steeper terrain features. Sluffs could have enough mass to push you around or into terrain traps like gullies or over cliffs.

Use caution above cliffs where small avalanches may have severe consequences.If triggered the loose dry sluffs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Feb 27th, 2019 2:00PM