Boletín de aludes

Kootenay Boundary

Mar 7 – 8, 2022Avalanche Canada
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Archivado · caducó 5 years ago

Peligro de aludes

Wed
Thu
Alta montaña
2 · Moderado
Límite del bosque
3 · Notable
Bajo el límite
1 · Débil
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Lo esencial

March is a notoriously tricky time with snowpack complexity is at its peak and this year is no exception. Recent storm snow sitting on a weak layer has been reactive to human traffic around treeline. We also remain suspicious of several other weak layers deeper in the snowpack.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible - Likely
    Tamaño
    2–3.5

    Weak layers from February (mostly crusts and surface hoar) are likely down around 60 cm and may become more reactive as the overlying snow settles into a denser slab. Two weak layers of surface hoar from January are likely down 100 cm or more and are primarily a concern in the east half of the region on northerly aspects around treeline. 

    A 1-5 cm thick crust that formed in early March could make it more difficult to affect these layers with the weight of a human or snowmobile, BUT if you aren't feeling the crust underneath you, or if you feel like your turns are digging in below it, choose simpler terrain and give avalanche terrain a wide berth. Remote triggered avalanches have been recently reported on this layer.  

    Diligent terrain selection is required for this type of avalanche problem. Signs of instability may not be visible on the surface, and the resulting avalanches will be large. An important part of your strategy would be to avoid rocky start zones below ridgetops and convex rolls. 

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible - Likely
    Tamaño
    1–2

    Human triggering of storm slabs should remain on your radar. Thursday night's snow is settling into a denser slab, and it may slide easily on the underlying crust that has been reported as high as 2250 m.  

    Test the bond of new snow on smaller terrain features with low consequences as you travel through various elevation bands and aspects.

    If you don't find a crust on or near the surface, or if you easily break through the crust, it will be possible to trigger avalanches deeper in the recent storm snow. 

    Cornices have grown during the last system as well so give them a wide berth.

Confidence

Moderate -

Weather Forecast

Sunday night: Increasing cloud. Moderate northwest ridgetop wind. Treeline temperature around -5 °C. Freezing level valley bottom.

Monday: Partly cloudy. Moderate northwest ridgetop wind. Treeline high around -1 °C. Freezing level rising to 1600 m. 

Tuesday: Flurries up to 5 cm. Light wind. Treeline high around -10 °C. Freezing level valley bottom.

Wednesday: A mix of sun and cloud. Light wind. Treeline high around -12 °C. Freezing level valley bottom.

Avalanche Summary

On Friday and Saturday, several accidentally triggered storm slab avalanches were reported in the northeast of the region. These avalanches were:

  • Large, ranging from size 2-3
  • Triggered by skiers, snowmobiles and snow cat. At least one was remote.
  • At treeline elevations, on leeward SE-NE aspects.
  • See photos and detailed description of the remote in this MIN

Similar incidents also occurred east of Slocan in the neighboring South Columbia region, resulting in a partial burial and injury. More details and photos here. 

Small loose wet avalanches were also reported on solar aspects in the afternoon.

East of Kelowna, a natural wind slab avalanche and several explosive triggered wind slabs were reported up to size 1.5 on east through south aspects around treeline. 

On Thursday, south of Nelson, avalanche control with explosives triggered several small to large avalanches, failing below the crust that formed on Wednesday.

Snowpack Summary

A near-surface crust may make for challenging travel conditions up to 2250 m. The crust ranges from breakable to supportive and is between 1-5 cm thick. 

20-50 cm of recent storm snow sits over a variety of surfaces including a weak layer of surface hoar in wind-sheltered areas around treeline and a crust on solar aspects.

Weak layers from mid-February and late January made up of crusts and/or surface hoar crystals can be found around 60-100 cm deep. Some recent persistent slab avalanches on this layer have surprised riders, so keep this type of avalanche in mind when making terrain choices.

Terrain and Travel

  • Approach steep, open and/or sparsely treed slopes cautiously.
  • Avoid steep convexities or areas with a thin, rocky, or variable snowpack.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • A crust on the surface will help bind the snow together, but may make for tough travel conditions.
  • Closely monitor how the new snow is bonding to the crust.

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