Avalanche Forecast

Issued: Dec 8th, 2016 4:55PM

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

Avalanche Canada jsmith, Avalanche Canada

Recently formed wind slabs are primed for human triggers. The first sunny day will make these slabs increasingly sensitive, even with arctic air temperatures.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Friday: Sunny / Strong to moderate easterly winds diminishing in the afternoon / Strong inversion with a alpine high of -14 C.Saturday: Sunny / Light easterly winds / Alpine high of -15 C.Sunday: Sunny / Light to moderate southwesterly winds / Alpine high of -12 C.

Avalanche Summary

Wind slab avalanches are a big concern in all areas within the region, and could easily step down to the surface hoar layer below. This surface hoar layer may remain reactive to human triggers for a longer period than is common for this region because it is being well preserved my cold temperatures. Last weekend, there were a couple of close calls with people being surprised by the touchiness of the buried surface hoar layer.

Snowpack Summary

The storm from last weekend brought 30-80 cm of cold powder. This new snow has been blown around by the wind - first by southwesterly winds during the storm, then by northerly winds with the onset of arctic air, and now by easterly outflow winds. As a result, expect wind slabs in a wide variety of locations. Unless you're really certain about the recent local wind history, the safest bet is to assume wind slabs could be present on all aspects in exposed alpine, treeline, and even some below treeline locations. The recent snow buried a surface hoar layer, which now lies 60-120 cm in many parts of the region. This layer was reactive during and after the storm and is likely still reactive to human triggers. A thick rain crust exists 20-30 cm below the surface hoar layer, with isolated reports of weak facets (sugary snow) forming above the crust; however, that interface hasn't become a concern as of yet. Treeline snow depths are around 140-200 cm in the Terrace and Stewart areas, but substantially less further north. Concerns in the north are basal weaknesses that may exist in the shallower snowpack areas especially on smooth alpine features like glaciers.

Problems

Wind Slabs

An icon showing Wind Slabs
Winds have switched from southeasterly, then northerly, now easterly. Outflow winds are blowing at low elevations as well as high. Touchy wind slabs exist on a wide variety of exposed slopes.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Avoid areas of wind slab. Switching winds may have reverse loaded slopes and may surprise you.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
A persistent weak layer mostly comprising of touchy surface hoar is buried 60-120 cm deep throughout the region, and is currently reactive to human triggers.
Avoid slopes where buried surface hoar is preserved. Remote triggering from a distance is possible.Dig down to find and test weak layers before committing to a line.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Dec 9th, 2016 2:00PM

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