Avalanche forecast

South Columbia

Dec 27, 2016Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Tuesday's danger ratings are based on about 15cm of new snow. If new snowfall amounts are greater than 20cm in your riding area, the avalanche danger may be High.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–2
    New snow and wind forecast for Monday night and Tuesday will form new wind slabs in exposed higher elevation terrain. In the Monashees, where more snow is expected, you will likely find a more widespread storm slab problem.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    1–3
    A weak layer buried mid-December now lies up to 75cm 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.

Confidence

Moderate - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

Tuesday: 15-30cm of new snow / Strong westerly winds / Freezing level at valley bottomWednesday: Overcast skies and light flurries / Moderate westerly winds / Freezing level at valley bottomThursday: 5-10cm of new snow / Moderate westerly winds / Freezing level at valley bottom

Avalanche Summary

There were reports of a few very soft slabs failing over steep rolls on Sunday. These avalanches occurred in response to locally moderate amounts of new snowfall on Saturday. Of note, there was a a size 2 persistent slab avalanche triggered on an east facing alpine feature on the north side of the highway in Roger's Pass. The avalanche, which was reported to have failed on the mid-December weak layer, was remotely triggered from a distance of 30 metres. Although this seemingly isolated avalanche occurred in a different forecast region, this event may point to a pattern of increased activity on the mid-December layer which may also extend into the South Columbia region. With new snow and strong winds forecast for Monday night and Tuesday, I'd also expect new wind slab activity in higher elevation terrain on Tuesday.

Snowpack Summary

On Tuesday, new snow and wind are forecast to form fresh wind slabs in exposed higher elevation terrain. 40-70 cm of snow now overlies the mid-December interface which consists of a variety of old snow surfaces including 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 from the North Columbia region suggest this layer may be 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.

Regions covered