Avalanche forecast

Northwest Coastal

Mar 24 – 25, 2016Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
1 · Low
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Highlights

Light snowfall and ongoing southwest winds are expected to continue to from fresh wind slabs at and above treeline this weekend.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Continued light snowfall and moderate southwest wind will likely continue to build fresh wind slabs at treeline and in the alpine. Wind slabs may be particularly reactive due to underlying hard surfaces.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    Some cornices are the size of a bus, and will continue to grow with forecast snow and wind. Cornice collapses in the region continue to trigger large avalanches on the slope below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–6
    A few persistent weaknesses exist in the mid snowpack (see snowpack description). These potentially destructive layers may become reactive with spring warming or with a large trigger such as a cornice fall.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain on Saturday

Weather Forecast

The Northwest Coast should see a steady progression of relatively weak frontal bands through the weekend. FRIDAY: Freezing level around 1200 m, 1 to 5 cm of snow, light to moderate southwest winds. SATURDAY: Freezing level around 1200 m, 2 to 15 cm of snow, moderate to strong south winds. SUNDAY: Freezing level holding at 1200 m, light convective flurries, light variable winds. For more detailed mountain weather information visit avalanche.ca/weather

Avalanche Summary

No new activity to report from Wednesday. In the north of the region near Stewart, a few persistent and deep persistent slab avalanches to size 2.5 were reported on Tuesday. The avalanches were triggered by solar radiation or by large cornices falls. One of the avalanches (which was triggered by a cornice fall) occurred on a northwest aspect at about 1400 m and is thought to have failed on the March 3rd surface hoar. The slab was 50 cm deep, 40 m wide and 80 m long.

Snowpack Summary

In the last 48 hours 5 to 10 cm of snow has fallen accompanied by moderate to strong southerly winds. At treeline and in the alpine small wind slabs are expected to have formed. These wind slabs overlie a variety of surfaces which include a hard crust on solar aspects above 1300 m, moist or refrozen snow on all aspects below 1300 m, and settled wind slabs in exposed high elevation terrain. A layer of surface hoar or melt-freeze crust buried on March 3 is down 50-80 cm and has been on the radar of professionals in the mountains north of Stewart. A more widespread crust/facet layer buried in early February can now be found down over a metre. Both of these deeper layers have become less likely to trigger, but have the potential for large avalanches especially with a large trigger such as a cornice fall. I'd be increasingly cautious during periods of warming or solar radiation.

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