Avalanche forecast

Northwest Coastal

Jan 27 – 28, 2016Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

Heavy precipitation will continue to test weak layers and keep the Avalanche Danger HIGH.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–6
    A warm, wet and windy storm has overloaded persistent weak layers which lie more than 100cm below the surface. Even if the storm tapers-off on Thursday, I'd give the snowpack a few days to adjust to the new load before pushing into steeper terrain.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3

Confidence

Moderate - Freezing levels are uncertain on Thursday

Weather Forecast

Up to 30mm of precipitation is forecast for Wednesday night with another 5-10cm of snow expected on Thursday. Ridgetop winds will remain extreme from the southwest while freezing levels will drop throughout the day from 1600m to about 1000m. On Friday and Saturday the region will see light flurries, significantly decreased winds and freezing levels around 700m.

Avalanche Summary

On Tuesday observations were somewhat limited due to weather; however, professional operators in the region were still reporting fairly widespread explosive and naturally triggered storm and persistent slab avalanches to size 2.5. Many of the avalanches were suspected to have failed on the January 9th surface hoar. With the current wet and stormy conditions I suspect further observations will be limited, but we can expect new storm slab activity at elevations where precipitation falls as snow. More importantly, precipitation will add stress to buried persistent weak layers and will increase the likelihood of destructive persistent slab avalanches.

Snowpack Summary

A warm, wet and windy storm is forming dense new storm slabs at higher elevations while rain is saturating surfaces at lower elevations. The January 9th surface hoar/facet layer is down 70-120 cm in most places, and seems most concerning at and below treeline. Around the same depth you may also find a surface hoar/facet interface from around New Years. Ongoing reports of remote triggering, whumpfing, and sudden shears in snowpack tests are all indications that these layers are touchy and could propagate well if triggered. Deeper weaknesses are generally considered to be dormant.

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