Avalanche forecast

Northwest Coastal

Dec 15 – 16, 2020Avalanche Canada
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Avalanche danger

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

Substantial snowfall is expected in the far south of the region but the track of the system may shift. Treat the danger as HIGH if you find more than 30 cm of snowfall accumulation.

Avalanche problems

  • Storm Slabs

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

    Snow is expected to accumulate over the day with associated strong southwest wind. The most snow is forecast in the far south with substantially less accumulation in the northern half of the region. Slabs are likely to develop during the storm, particularly in wind-affected terrain features. Assess for slab development and the bond of the new snow with previous surfaces before committing to avalanche terrain.

  • Deep Persistent Slabs

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

    Weak faceted grains may overly a melt-freeze crust near the base of the snowpack. There is uncertainty on where this layer remains a problem in the region, but large avalanches have recently occurred in the northern half of the region. The most likely area to trigger it would be in thin, rocky snowpack areas.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

MONDAY NIGHT: Cloudy with snowfall, accumulation 15 to 25 cm near Kitimat and 5 to 10 cm for the remainder of the region, 40 to 60 km/h southwest wind, alpine temperature -4 C, freezing level 800 m.

TUESDAY: Cloudy with snowfall, accumulation 10 to 30 cm in the south of the region and 2 to 5 cm in the north, 60 km/h southwest wind, alpine temperature -4 C, freezing level 700 m.

WEDNESDAY: Cloudy with snowfall, accumulation 20 to 40 cm in the south of the region and 5 to 10 cm in the north, 40 to 60 km/h southwest wind, alpine temperature -5 C.

THURSDAY: Mix of sun and cloud with periodic snowfall, accumulation 5 cm, 20 to 40 km/h west wind, alpine temperature -7 C.

Avalanche Summary

A few naturally-triggered wind slab avalanches were observed around Bear Pass on Sunday. The last deep persistent slab avalanches released on December 11 in the north of the region near Ningunsaw.

Data in this region is very sparse. Please considering sharing your observations to the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter.

Snowpack Summary

The next snow storm is forecast for Tuesday, bringing substantial snowfall to the south of the region as well as strong southwest wind. Expect slabs to form during the storm, particularly in wind-affected terrain at and above treeline. The snow will fall onto previous wind-affected snow at higher elevations, potentially a layer of surface hoar in sheltered areas, and a crust at lower elevations.

The early-December crust is now down 100 cm in the alpine but close to the surface at and below treeline elevations. The early-November crust is buried around 100 to 200 cm at treeline elevations. The early-November crust may have weak and sugary faceted grains above it in parts of the region, which have produced large, full-depth avalanches in the past weeks. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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