Avalanche forecast

Northwest Coastal

Dec 31, 2015 – Jan 1, 2016Avalanche Canada
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Avalanche danger

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

Happy New Year! There are still several buried surface hoar layers in the top 100 cm of the snowpack. Initial warming from the sun followed by warm air in the alpine, may increase the sensitivity of these weak layers.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–4
    Several weak layers of surface hoar may be buried in the top 100 cm of the snowpack. Forecast warming of the storm slab above these weak layers is a concern for increased sensitivity to triggering and the possibility of longer fracture propagations.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    Storm slabs may exist in areas where the recent storm snow has settled into cohesive slab. Forecast warming may develop slabs where unconsolidated snow was recently found.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2
    Strong solar radiation and warming at higher elevations may increase the size and frequency of moist or wet loose snow avalanches.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

Mostly clear with freezing levels at valley bottoms and overnight valley temperatures around -10. Warm air has started to develop at higher elevations, between 1400-2100 metres. This warm air is not able to descend into the colder valleys. Forecast upper elevation southerly winds are expected to continue to push warmer air into the alpine. Friday is forecast to be the warmest day of this inversion for the northwest coastal region. Saturday and Sunday may continue to have alpine temperatures at or slightly below freezing. Clear nights should allow for the snow surface to re-freeze.

Avalanche Summary

Natural avalanche storm slab activity has tapered-off with the current clearing trend. However, human-triggered avalanches will remain a concern for the forecast period, especially at elevations or in parts of the region where recent storm accumulations have settled into a cohesive slab. Solar-induced loose wet avalanches up to size 1.5 have also been reported. The likelihood and size of loose wet avalanches will increase with warmer alpine temperatures expected during the forecast period.

Snowpack Summary

Solar radiation has started to affect the surface snow on southerly aspects, resulting in loose moist or wet releases and the beginnings of melt-freeze crusts overnight. The recent 25-40 cm of storm snow continues to facet due to the cold temperatures, and new surface hoar has been reported on all aspects and at all elevations. The forecast temperature inversion looks like it will be strongest on Friday, and our uncertainty revolves around how much warmth upper elevations will receive. It is also unclear  how storm slabs, especially those sitting on buried surface hoar layers (in the top 100 cm) will react to the warming. I suspect that outflow winds are transporting unconsolidated snow, and areas that are having or have received wind may continue to have wind slab problems. The winds have been variable across the region; Shames has reported very little wind and slightly west of there the wind effect has been widespread. The north of the region has been cold with temperatures around -20 in the valleys and alpine temperatures around -8 at 2000 metres. Watch for weak basal facets in colder and shallower snowpack areas.

Regions covered