Avalanche forecast

Northwest Coastal

Dec 24 – 25, 2016Avalanche Canada
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Avalanche danger

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

The incoming storm will build touchy wind slabs and possibly wake up weak layers buried by last week's storm.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3
    Large amounts of recent snow coupled with extreme winds built reactive slabs behind exposed terrain features. Winds slabs exist on all aspects, as recent winds have come from the northeast.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–4
    The early December cold snap has left several weak layers composed of surface hoar and facets buried about 1 metre deep. Additional loading from new snow and wind could potentially release large avalanches on these layers.

Snowpack Summary

Clear cold weather has limited settlement of the recent storm snow. New surface hoar (up to 15 mm) and sun crusts have been reported forming on the snow surface, and intense snow transport has been observed in the alpine. The region received up to 125 cm of new snow between 17 and 21 December. The new snow arrived with extreme winds, which has left widespread hard wind slabs in exposed terrain. All this new snow sits over a variable interface composed of hard wind slabs in wind exposed terrain, weak faceted (sugary) snow, and 5-10 mm feathery surface hoar in sheltered areas. The bond between the newer storm snow and this interface is a concern and could develop into a persistent slab problem. In areas with less snow, there are two additional layers that should be on your radar. The first is a layer of surface hoar that was buried in mid-November and may now be down around a metre in thinner spots. The second is an old rain crust from November that may have developed weak facets, particularly in the north of the region.

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

SUNDAY: Cloudy with afternoon flurries, southwest winds picking up throughout the day reaching 60 km/h by the afternoon and 100 km/h overnight, temperatures around -10C.MONDAY: Stormy with 20-40 cm of new snow, 40-60 km/h southwest winds, temperatures around -5C.TUESDAY: Stormy with 10-20 cm of new snow, 20-40 km/h southwest winds, temperatures around -5C.

Avalanche Summary

Wind slabs continued to be reactive on Friday, as reports included a rider-triggered size 2 soft slab on a north aspect at treeline and numerous explosive-triggered size 1.5-2.5 avalanches on east and northeast aspects. More reports confirm a large natural avalanche cycle producing up to size 3 avalanches occurred during last week's storm. In the northern part of the region where the snowpack is thinner, skiers have remotely triggered several size 1.5-2 deep persistent slab avalanches in steep shallow start zones (failing on weak sugary facets near the ground). With winds picking up on Sunday, expect wind slabs to remain touchy.

Regions covered