Avalanche forecast

Northwest Coastal

Apr 12 – 13, 2016Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
No rating
Treeline
No rating
Below
No rating
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Highlights

When the sun comes out on Wednesday, expect lots of solar triggered sluffing on steep slopes. New wind slabs are expected to be reactive in leeward features in the alpine.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    New snowfall and strong southerly winds likely formed new wind slabs in the alpine on Tuesday. These slabs will overlie a firm melt-freeze crust which may increase the slab reactivity and likelihood of triggering.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    The timing of failures is unpredictable. Unsupported sections are extra suspicious. Dropping chunks are a hazard in themselves and they may also trigger a slab avalanche on the slopes below. Watch and limit your exposure to overhead hazards.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    Loose wet sluffing is expected on steep slopes when the sun is out. The recent snowfall will be sliding on a firm crust which will likely increase the distance sluffs can travel.

Weather Forecast

A mix of sun and cloud is expected for Wednesday but light flurries may continue in the morning. Light southerly winds are expected in the alpine and afternoon freezing levels should be around 1400m. Mostly sunny conditions are expected Thursday morning with increasing cloudiness in the afternoon. Winds should remain light most of the day and afternoon freezing levels are expected to be around 1600m. Light snowfall is expected on Friday. Alpine winds are forecast to be moderate to strong from the southwest with afternoon freezing levels around 1300m.

Avalanche Summary

On both Sunday and Monday, loose wet avalanches up to size 2.5 were reported in the far north of the region. With the arrival of spring, field observations and data have become quite limited in the region. A lack of avalanche reports does not mean avalanches are not occurring. On Wednesday, newly formed wind slabs are expected to be reactive to human-triggering in the alpine. Widespread solar triggered loose sluffing is expected with the new snow sliding on the firm crust layer. Cornices have been weak recently and may fail naturally with storm loading.

Snowpack Summary

Prior to the new snowfall, dry winter snow was being reported on northern aspects above 1700m in the area north of Stewart. South aspect slopes and lower elevations were undergoing daily melt-freeze cycles. Around Terrace, melt-freeze conditions were reported at all elevations. The new snow will bury this crust and strong southerly winds in the alpine will build wind slabs. The region should return to melt-freeze conditions on Wednesday with surface crusts forming overnight and breaking down during the day. The snowpack's strength is directly related to the thickness and strength of these surface crusts. A widespread crust/facet layer from early February and depth hoar at the bottom of the snowpack (primarily in northerly & inland areas) are dormant. Cycles of melting and refreezing have limited the reactivity of these old layers. However these layers, or the ground, could potentially once again be the layer for an isolated yet large avalanche with prolonged periods of warming.

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