Avalanche forecast

Northwest Coastal

Dec 5, 2016Avalanche Canada
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Archived · expired 10 years ago

Avalanche danger

Mon
Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
No rating
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Highlights

Rider triggered storm slab avalanches are likely, especially where there is buried surface hoar. Use a very conservative approach to terrain and gather info while you travel.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3
    Persistent weak layers with surface hoar, facets, and crust are buried 60-100 cm deep throughout the region, and reportedly became reactive during the storm.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Touchy storm slabs still exist especially on leeward slopes that see more loading from the winds.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A cool arctic air mass will dominate the weather pattern over the next few days bringing cooler and much dryer conditions. Coastal areas may see some flurries and cloudy skies tonight and early tomorrow before the arctic front locks in on Tuesday. Skies will mostly be a mix of sun and cloud. Alpine temperatures will drop to -15 accompanied by light NE winds. Expect strong, cold outflow winds.

Avalanche Summary

On Saturday, ski tourers reported numerous persistent slab avalanches triggered remotely and running on the buried surface hoar interface. The avalanche crowns  were 50-100 cm deep, 200 m wide and 100 m long from northeast aspects at upper elevations. They also noted another avalanche from a distance away running 500 m in length and width. Rider triggers are likely on Monday where this instability exists.On Friday, explosive triggered storm slabs were reported from northerly aspects at 1400 m and above up to size 2.5. Some of these ran on the buried surface hoar layer. At treeline and lower elevations numerous loose wet natural avalanches were reported from steep, rocky terrain features. Natural avalanches are still possible and rider triggered avalanches remain likely through Monday. Light winds from the northeast may reverse load slopes and catch you by surprise.

Snowpack Summary

Storm snow totals reached 30-75 cm by Sunday, with the potential for much more on lee features due to strong southwest winds. The new snow buried a surface hoar layer reported 60-100 cm below the surface in many parts of the region. This layer was reportedly reactive during the storm. 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. Treeline snow depths are around 120-140 cm in the Terrace and Stewart areas, but substantially less further north.

Regions covered