Avalanche forecast

Northwest Coastal

Dec 17 – 18, 2011Avalanche Canada
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Avalanche danger

Mon
Tue
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Wind slabs have formed on lee and cross-loaded features. They may be touchy, reactive, and propagate far. Loading may have occurred lower on the slopes due to strong winds in some parts of the region.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Storm slabs exist at all elevations. They may be particularly reactive in areas where there is a weak buried surface hoar/crust/facet interface.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday

Weather Forecast

Mostly clear skies are forecast for sunday morning with freezing levels at or near surface. Late in the day another frontal system will hit the region bringing up to 50cm of snow overnight and throughout monday. Strong southwest winds and freezing levels of 900m will accompany this system.Tuesday calls for light to moderate snowfall in the morning, cooler temperatures and reduced westerly winds.

Avalanche Summary

Control work with explosives during the week produced numerous avalanches up to size 2.5 on a variety of aspects and elevations. On Wednesday widespread natural avalanches up to size 2 were reported. These avalanches all ran on the mid-December buried surfaces ( surface hoar, melt-freeze crusts). With the intense wind and snow forecast for monday we can expect another significant natural avalanche cycle.

Snowpack Summary

The southern part of the region has received up to 70-90cm of snow over the past 5 days (Kasiks, Terrace areas) and less snowfall to the north. This has formed storm slabs at all elevations. This new snow has been blown around by strong southwest winds creating new wind slabs on lee slopes. Buried beneath the new snow sits a variety of weak snow surfaces (surface hoar, melt-freeze crusts, and facetted snow). This crust is up to 20cm in thickness and extends up to alpine elevations in the south, and around 1000m in the north. The surface hoar growing on the crust was sized up to 10mm. A strong temperature gradient in the top 30cm was also reported to be faceting snow below the surface crust. These layers have met their threshold, and while widespread avalanche activity has occurred lots more is expected with monday's forecast weather. The mid and lower snowpack are well settled and strong.

Regions covered