Avalanche forecast

Northwest Coastal

Feb 11 – 12, 2016Avalanche Canada
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Avalanche danger

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

A series of new storms are expected to develop new storm slabs at higher elevations. Deeply buried persistent weak layers continue to be a concern for large avalanches.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    The deeply buried persistent weak layer of surface hoar was reactive during the last wet storm. It has not cooled off much, and more warm wet weather is forecast. Uncertainty with this layer requires conservative terrain selection.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    New storm slabs are expected to develop in the alpine, and possibly at treeline if the freezing level drops more than forecast.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    Moist or wet snow may continue to release naturally or with light additional loads until the freezing levels drop.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Strong southeast winds overnight with light precipitation and freezing levels around 800 metres. Moderate southwest winds with 10-15 mm of precipitation on Friday and freezing levels around 800-1000 metres. Light precipitation and moderate southerly winds on Saturday with freezing levels between 700-1000 metres. Moderate to heavy precipitation on Sunday with moderate southwest winds and rising freezing levels. Heavy precipitation is forecast for Monday.

Avalanche Summary

Explosives control on Thursday resulted in a size 2.5 slab avalanche that released on the persistent weak layer in the north of the region in the Ningunsaw area. On Wednesday, several loose wet slides were reported from the Shames backcountry that were visible in the Geronimo bowl. On Tuesday explosives control in the Bear Pass highway corridor produced slab avalanches in the alpine up to size 4.0 with wide fracture propagations. Reports of natural activity during the recent storm of slab avalanches up to size 4.0 releasing in the storm snow or on the deeply buried persistent weak layer from early January.

Snowpack Summary

Observations have been sparse due to poor flying and travel conditions, as well as poor visibility. In the Shames backcountry on Wednesday there was no crust at 1300 metres ( the highest point the observer reached), and we suspect the crust is only above 1500 metres. There was 50 cm of recent storm snow, with the top 25 cm being rain soaked. This moist and wet storm snow was sitting on the old crust from the previous warm storm at the end of January. Compression tests resulted in moderate shears within the storm snow and on the old crust. The January 9th surface hoar/facet layer is down 70-200 cm across the region and remains a concern for commercial operations. There continues to be a lot of uncertainty regarding the reactivity and distribution of this destructive persistent avalanche problem; however, warm temperatures have increased the likelihood of triggering these layers where they still exist. A very conservative approach to mountain travel is still required.

Regions covered