Avalanche forecast

Northwest Coastal

Mar 10, 2017Avalanche Canada
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Avalanche danger

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

It's time to dial back terrain choices at all elevation bands. A buried persistent weak layer has created the potential for surprisingly large avalanches.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Recent snow accumulations are expected to have been shifted into fresh wind slabs in exposed lee terrain. These surface instabilities have the potential to step-down to deep, more destructive layers.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    A mix of persistent weak crystals lurk up to 150cm below the surface, and have the potential for surprisingly large avalanches. Conservative terrain selection remains critical for the foreseeable future.

Confidence

High -

Weather Forecast

Friday: Mainly clear skies / Moderate easterly winds / Alpine temperature of -15Saturday: Overcast skies with light flurries / Moderate easterly winds / Alpine temperature of -12Sunday: 15-30cm of new snow / Moderate southerly winds / Alpine temperature of -5

Avalanche Summary

On Monday two avalanches were simultaneously remotey-triggered below treeline west of Terrace. See here for the excellent details in the Facebook post. We had reports of two rider-triggered wind slab avalanches (Size 1.5 and 2.0) southwest of Terrace on Sunday. In both cases the crown height was 50cm and shooting cracks were also reported in mellow terrain. There was a remote-triggered Size 1 in the Shames backcountry, also with a 50cm crown, running on a weak facet layer.  These avalanches speak to the touchy persistent avalanche problem in the region.Strong winds on Thursday should promote a new round of wind slab activity. The persistent slab problem is expected to remain touchy as the recent storm snow settles into a cohesive slab over top of the late February persistent weak layer.

Snowpack Summary

On Tuesday night the region received between 5-40cm of new snow with the greatest accumulations occurring in the south of the region. Southwest winds and more recent easterly winds are expected to have redistributed this new snow forming fresh wind slabs on a variety of aspects. 70-150 cm below the surface you'll find a variety of old surfaces which were buried in late February. These weak surfaces, which remain the primary concern in the region, include surface hoar, facets, stiff wind slabs and a melt-freeze crust below 1600 m. The overlying slab remains reactive on this interface, with ongoing reports of whumpfing in flat terrain. Moreover, we've had reports of sudden, propagation-likely test results on this layer. Below this interface the snowpack is generally settled and strong, with the exception being shallow snowpack areas around Bear Pass and Ningunsaw where basal facets remain an ongoing concern.

Regions covered