Avalanche Forecast

Issued: Dec 30th, 2016 3:55PM

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

Avalanche Canada jlammers, Avalanche Canada

A touchy weak layer has the potential for large avalanches, and is primed for triggering. Conservative terrain selection is critical.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Friday

Weather Forecast

Friday evening: 10-15cm of new snow / Extreme westerly winds / Alpine temperatures of -3Saturday: Lingering flurries in the morning with clearing in the afternoon / Extreme northerly winds / Alpine temperatures of -10Sunday: Clear skies / Extreme northerly winds / Alpine temperatures of -10Monday: Clear skies / Moderate northerly winds / Alpine temperatures of -3

Avalanche Summary

Persistent slab avalanches to size 2 were reported to be triggered remotely or under light loads in the Terrace backcountry on a layer of surface hoar buried 30-60 cm below the surface. One report, accessible on the MCR website mountainconditions.com, mentions wide propagations and avalanches running in low angled terrain. Check out the great Mountain Information Network posts as well for other detailed reports.

Snowpack Summary

Recent storms have deposited 50-80 cm new snow combined with strong, mainly southwest winds. The storm snow has buried a layer of feathery surface hoar (up to 15 mm in sheltered areas), making wide propagations possible. Recent reports from Shames indicate the slab properties overlying this layer of surface hoar are supporting easily triggered avalanches, including avalanches running in low angled terrain. An earlier (and therefore deeper) weak interface that formed during the early December cold snap can be found in isolated areas buried 100-150 cm deep. The layer consists of preserved surface hoar or weak faceted (sugary) snow. The lower snowpack is well consolidated in deep snowpack areas. In shallow snowpack areas, especially north of Ningunsaw, an old rain crust near the bottom of the snowpack has developed weak facets and might be triggerable from a thin or rocky area on a convex slope.

Problems

Persistent Slabs

An icon showing Persistent Slabs
A recently buried surface hoar layer is highly sensitive to human triggering and has given a few people a scare in the Terrace area. Brief warming on Friday night may add cohesion to the slab allowing it to propagate over wider distances.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.Use conservative route selection, stick to moderate angled terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

2 - 3

Wind Slabs

An icon showing Wind Slabs
Up to 15cm of new snow may fall on Friday night. Extreme westerly winds are forecast to shift these accumulations into new wind slabs in exposed lee terrain. Forecast winds may also increase the reactivity of deeper surface hoar layers.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.Avoid steep lee and cross-loaded slopes

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Dec 31st, 2016 2:00PM

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