Avalanche forecast

Northwest Coastal

Mar 8 – 9, 2022Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low
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Highlights

It's going to be a sunny day! The wind will change direction to northeast, developing fresh wind slabs throughout the day. Wind slabs formed by previous extreme northwest wind might still be reactive to human triggers.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2

    The wind will change direction to northeast and is forecast to become strong in the morning. Fresh wind slabs will build behind ridge crests and in lee terrain features in the alpine and exposed treeline.

    On Sunday, strong to extreme wind from the northwest formed wind slabs. These slabs might still be reactive to human triggers and might be found farther down slope than expected due to the strength of the wind. 

    Triggered wind slabs might step down to deeper buried weak layers and result in larger avalanches. 

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    1–2

    Cornices are large and can become weak with sun exposure. Caution around slopes that have cornice hazard above. Keep in mind that firm cornices can pull back into flat terrain at ridgetop if they fail. 

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    1.5–2.5

    A layer with weak, feathery surface hoar crystals is buried 25-50 cm deep at sheltered treeline features and in the lower alpine.

    A thick crust is buried 60-100 cm deep. Avalanches on this layer will likely reach large sizes.

    A few, skier triggered avalanches and isolated natural activity up to size 2 were reported on both layers in the last few days.

Confidence

High -

Weather Forecast

Monday night: Cloudy with clouds clearing towards the morning, up to 2 cm snow, light northeast wind, alpine low -6 °C, freezing level at valley bottom. 

Tuesday: Sunny, moderate to strong northeast wind, alpine high -7 °C, freezing level at 600 m. 

Wednesday: Sunny, strong northeast wind, alpine high -6 °C, freezing level at 400 m.

Thursday: Cloudy, 5 cm new snow, moderate to strong southwest wind, alpine high -5 °C, freezing level at 400 m.

Avalanche Summary

On Sunday, a large (size 3) wind slab released naturally in steep alpine terrain and several small natural wind slab avalanches up to size 1.5 were reported. One was triggered by a failed cornice. Skiers triggered small (size 1) wind slabs on south, east and north facing slopes in the alpine. Loose wet avalanche activity to size 1.5 was observed on steep sun-exposed slopes.

There have been a few, skier triggered slab avalanches to size 2 on the two buried persistent weak layers described in the Snowpack Summary over the last few days. 

A skier triggered a large (size 2) avalanche on a north aspect in the alpine on Saturday. The avalanche released on a crust and was about 70 cm deep. 

On Friday, skiers triggered small (size 1) avalanches on a northeast aspect that released on the buried surface hoar layer. A natural large slab avalanche was also observed on a northeast aspect that likely released on the same layer. A natural cornice fall triggered a wind slab on the slope below and resulted in a size 2 avalanche.

Snowpack Summary

There's a lot going on in the upper snowpack. Careful assessment is recommended. 

There is a crust on the surface at lower elevations and on solar aspects at treeline.

Feathery, weak surface hoar crystals buried around February 26th are found down 25-50 cm, most prominently at treeline elevations. This layer has been reactive to skier traffic in the last few days. 

A thick crust buried in mid-February is now found down 60-100 cm. Skiers also triggered avalanches on this layer in the last few days.  

The lower snowpack is effectively bridged by the layers above, and we do not expect avalanches to be triggered in the lower snowpack at this time. 

Terrain and Travel

  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Minimize your exposure time below cornices.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of a buried crust.

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