Avalanche forecast

North Rockies

Jan 2 – 3, 2021Avalanche Canada
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Avalanche danger

Mon
Tue
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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Highlights

20 to 40 cm of snow is expected Friday night with another 10 to 15 cm incoming Saturday. Touchy storm slabs are expected & there is real concern that storm slabs in motion will step down and trigger very large persistent slab avalanches. Avoid avalanche terrain Saturday.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3.5

    Previous to the incoming storm snow, 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. This storm is likely to initiate a natural avalanche cycle that could easily trigger 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

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–2

    20 to 40 cm of snow is expected Friday night with another 10 to 15 cm incoming Saturday. 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

Moderate - 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 whether buried persistent weak layers become active, triggering avalanches, with the arrival of the forecast weather.

Weather Forecast

A warm wet storm descends upon the region this weekend.

FRIDAY NIGHT: Freezing level around 1500 m, 20 to 40 cm of snow possible at upper elevations, potential for heavy rain in the valleys. Larger precipitation amounts are expected along the western edge of the region. Strong to extreme southwest wind.

SATURDAY: Overcast, freezing level around 1500 m, 10 to 15 cm of snow possible during the day with another 5 to 10 cm possible Saturday night, strong to extreme southwest wind.

SUNDAY: Broken cloud cover, freezing level around 1000 m, strong west/southwest wind, up to 5 cm of snow possible.

MONDAY: Broken cloud cover, freezing level lowering to valley bottom, strong southwest wind, trace of snow possible.

Avalanche Summary

A natural avalanche cycle is expected to begin Friday night, likely carrying on into Saturday.

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

20 to 40 cm of new snow is expected by Saturday morning.

Previous to the new snow, 30 to 80 cm of settled snow was 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, wind, or rain.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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