Avalanche forecast

Northwest Coastal

Dec 12, 2016Avalanche Canada
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Archived · expired 10 years ago

Avalanche danger

Mon
Tue
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

A weak layer of surface hoar that is now buried around a metre deep is creating a low likelihood, high consequence scenario. Continue to investigate this layer carefully.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2
    Recently formed wind slabs may remain reactive to human triggers for several days after the winds die down. Wind slabs may be present on many aspects and elevations due to strong and highly variable wind directions.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–3
    A persistent weak layer of touchy surface hoar is buried 60-120 cm deep throughout the region, and may be reactive to human triggers. Smaller wind slabs may step-down to this layer resulting in large avalanches.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Monday: Sunny / Light easterly winds / High of -13 C.Tuesday: Sunny / Light northeasterly winds / High of -13 C.Wednesday: Sunny / Light northeasterly winds / High of -12 C.

Avalanche Summary

On Sunday, there was a report of a size 2 natural avalanche west of Terrace. It was on a southwest aspect and it was estimated that it failed on the mid-November surface hoar layer around a metre deep. This layer may remain reactive to human triggers in isolated locations for weeks and requires continued investigation.

Snowpack Summary

Clear skies and strong outflow winds have created a variety of snow surfaces including scouring and hard wind slabs in exposed areas and up to 12 mm surface hoar formation in sheltered areas. Strong to extreme easterly winds over the past few days have created wind slabs on aspects you may not expect them. Wind slabs could be present on all aspects in exposed alpine, treeline, and even some below treeline locations. A layer of surface hoar which was buried around November 22nd is down 60-120 cm in many parts of the region. This layer is likely still reactive to human triggers. A thick rain crust exists 20-30 cm below the surface hoar layer, with isolated reports of weak facets (sugary snow) forming above the crust; however, that interface has not become a concern as of yet. Treeline snow depths are around 140-200 cm in the Terrace and Stewart areas, but substantially less further north. Concerns in the north are basal weaknesses that may exist in the shallower snowpack areas especially on smooth alpine features like glaciers.

Regions covered