Boletín de aludes

North Rockies

Jan 3 – 4, 2021Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Tue
Wed
Alta montaña
4 · Fuerte
Límite del bosque
4 · Fuerte
Bajo el límite
3 · Notable
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Lo esencial

Avalanche Danger is greatest in the North where the storm has produced more than 55 cm of snow. Continued snowfall & strong wind has resulted in dangerous avalanche conditions. The rating in areas that receive less than 25 cm in total from the storm should be CONSIDERABLE.

Problemas de aludes

  • Persistent Slabs

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

    Previous to this weekend's storm, a buried persistent weak layer has been observed throughout the region 30 to 80 cm below the surface. The catch is that this layer is present on some slopes, and then absent on nearby slopes. As the weekend storm progresses, a natural avalanche cycle may begin that could easily include very large persistent slab avalanches. It will be a good test in the long run, but this is a time to avoid avalanche terrain while the snowpack tries to sort itself out. 

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Very Likely
    Tamaño
    1.5–2.5

    As of Saturday afternoon the storm has produced 10 to 55 cm of snow and more is expected to fall Saturday night into Sunday. Storm slabs will likely be susceptible to human triggering and there is real concern that storm slabs in motion will step down and trigger very large persistent slab avalanches.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to extremely variable snowpack conditions reported through the region. Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

A warm wet storm continues to impact the region Sunday before giving way to cooler temperatures Monday.

SATURDAY NIGHT: Freezing level around 1300 m, 1 to 5 cm of snow possible, strong west/southwest wind.

SUNDAY: Overcast, freezing level around 1100 m, strong west/southwest wind, 5 to 10 cm of snow possible.

MONDAY: Scattered cloud cover, freezing level at valley bottom, moderate southwest wind, 2 to 5 cm of snow possible.

TUESDAY: Scattered cloud cover, freezing level beginning at valley bottom rising to about 1500 m by sundown, strong to extreme southwest wind, trace of snow possible.

Avalanche Summary

On Friday natural storm slabs to size 2 were reported. Recent observations have been scant, but there were a few large human-triggered persistent slab avalanches in the neighbouring Cariboo region last weekend (on northeast slopes near treeline).

The persistent slab avalanche problem is now a low-probability/high-consequence situation. There were many notable avalanches between Dec 18-20 including natural, accidental, and remotely triggered avalanches up to size 2.5 at Pine Pass, Torpy, and Tumbler Ridge. This weekend's storm is likely to produce similar activity and should be a great test for our snowpack in the long term.

Snowpack Summary

The region has picked up 10 to 55 cm from the Friday/Saturday storm with the deeper amounts being found to the north. 40 to 120 cm of snow is now sitting above a mix of interfaces that were buried in early December. In some (but not all) terrain these interfaces may be composed of weak surface hoar or weak crusts and facet layers, creating a persistent slab avalanche problem. 

We do not see a clear pattern in which parts of the region or which types of terrain this problem is still a concern. 

Between Dec 18-20 there was compelling evidence of this problem around Pine Pass, the McGregors, and Tumbler Ridge. This problem has not been found at Renshaw, but has been found in the surrounding areas near McBride. There is no recent information from Kakwa. Overall, uncertainty about these layers make it difficult to have confidence in challenging or complex avalanche terrain without very careful terrain evaluation and an in-depth understanding of local snowpack conditions.

Snow depths are in 150-250 cm around Pine Pass, the McGregors, and McBride and closer to 100-150 cm around Tumbler Ridge. In shallower areas along the eastern slopes there could be weak snow at the bottom of the snowpack that could be a concern in steep rocky alpine terrain.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • In times of uncertainty conservative terrain choices are our best defense.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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