Avalanche Forecast

Issued: Dec 27th, 2016 4:21PM

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

Avalanche Canada jlammers, Avalanche Canada

Winds will play a large role in driving the avalanche danger on Wednesday as there's lots of loose snow available for redistribution. Use extra caution if the snow feels stiff or slabby.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Tuesday night: 10-15cm of new snow / Strong westerly winds / Alpine temperatures of about -13Wednesday: Light flurries / Strong westerly winds / Alpine temperatures of about -13Thursday: 10-15cm of new snow / Strong southerly winds / Alpine temperatures of about -10Friday: Light flurries / Moderate westerly winds / Alpine temperatures of about -12

Avalanche Summary

A Mountain Information Network post from the Adamant Range on the eastern side of the Selkirks indicated several avalanches failing on the mid-December weak layer throughout last week. The avalanches were in the size 1-2.5 range and were failing under light loads, in some cases naturally or remotely. On Christmas Day, there was another MIN post where a size 2 slab avalanche was triggered on an alpine slope on Video Peak in Glacier National Park. The avalanche, which was thought to have failed on the mid-December layer, was triggered remotely from a distance of 30 metres. Both of these avalanches point to the potentially touchy nature of the mid-December layer in some areas. No new avalanches were reported at the time of publishing this bulletin on Tuesday. I'm sure there was some natural wind slab activity in response to new snow and wind on Monday night. Continued strong ridgetop winds should promote ongoing wind slab activity. For the short term, I also expect loose dry avalanches to be triggered easily in steep sheltered terrain.

Snowpack Summary

Between 20 and 65 cm of new snow fell on Monday night with the highest accumulations occurring in the Monashees. In higher elevation terrain where the winds were stronger, these accumulations have likely been shifted into much deeper and potentially reactive wind slabs. In areas sheltered from the wind, the new snow is mostly loose and unconsolidated. 50-90cm below the surface you'll find the mid-December interface which consists of wind affected snow, faceted (sugary) crystals, and/or surface hoar crystals. Recent tests suggest the the new snow is well bonded to the interface in most areas. However, this layer is still reactive in some snowpack tests and should be investigated before pushing into steeper terrain. Limited observations suggest this layer has been especially touchy on the eastern side of the Selkirks. The thick mid-November crust layer typically sits 1-2 m down in the snowpack. Recent test results on this layer suggest it is generally well bonded to the adjacent snow with the possible exception of shallow snowpack areas. This layer is considered dormant at this time but remains an isolated concern that we will likely be tracking through much of the season.

Problems

Wind Slabs

An icon showing Wind Slabs
Up to 65 cm of new snow fell on Monday night and Tuesday. In higher elevation terrain where the winds were stronger, these accumulations may have been shifted into much deeper and potentially reactive wind slabs.
Be alert to conditions that change with elevation.Avoid areas where the surface snow feels stiff or slabby.Be cautious as you transition into wind affected terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

An icon showing Persistent Slabs
A weak layer buried mid-December now lies up to 90cm below the surface and has the potential for large avalanches. It's a tricky one to manage as it's not a problem in all areas. If in doubt, err on the side of caution and to stick to mellow terrain.
Dig down to find and test weak layers before committing to a line.Be aware of the potential for large avalanches due to the presence of buried persistent weak layers

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Loose Dry

An icon showing Loose Dry
With all the unconsolidated low-density snow that has accumulated over the past few days, I'd be on the look-out for loose dry avalanches in gullies and other steep features that were sheltered from the wind.
Be cautious of sluffing in steep terrain.Use safe ski cutting techniques before entering ski run.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Dec 28th, 2016 2:00PM

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