Avalanche forecast

South Coast

Jan 6 – 7, 2015Avalanche Canada
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Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

Tricky conditions are expected for Wednesday with a new storm slab sitting on a potentially touchy weak layer. Don't let the warm air and sunny conditions make you over confident.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–6
    Persistent weak layers down around 1m remain a concern. A smaller avalanche may step down to one of these layers or a heavy trigger like a cornice fall may be able to trigger one of these layers.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–5
    Warm temps and rain have caused the recent storm snow to settle into a cohesive slab. This slab may overlie a touchy weak layer. Give the new snow a chance to stabilize before pushing into avalanche terrain. Moist or wet storm slabs are possible.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    The moist or wet snow surface may produce wet sluffing on steep terrain features. Use extra caution on or below sunny slopes. A wet sluff has the potential to trigger a larger slab avalanche.

Confidence

Fair

Weather Forecast

A ridge of high pressure should keep the south coast dry for the next three days. Wednesday should be mostly sunny with light alpine winds and freezing levels around 3000m. A temperature inversion is expected and the warmest air (+5 deg C) is expected to sit around 2000m. Similar conditions are expected on Thursday with freezing levels around 3000m, a mix of sun and cloud, and light winds. On Friday, mostly cloudy conditions are expected with freezing levels beginning to fall progressively. The next weak storm system is currently forecast to arrive Friday night and it looks like freezing levels will be back down below 1000m.

Avalanche Summary

No new avalanches have been reported but this probably speaks to a lack of observers during the storm.  Natural slab avalanches up to size 2.5 were reported in the Sea-to-Sky region on Tuesday. Skier triggered slabs remain the main concern for Wednesday with the storm slab possibly sitting on a touchy weak layer.

Snowpack Summary

At the end of the storm, freezing levels rose and rain fell on the new storm snow. The storm slab sits on a previously variable snow surface that included wind affected surfaces (crust, hard and soft slabs), a freezing rain crust or sun crust, and surface hoar or sugary facets in sheltered shady terrain. The bond between the storm slab and the layer below is currently unknown but is expected to remain reactive on Wednesday. Cornices are expected to be weak with the current warming.  In the middle and lower snowpack we might find the mid-December surface hoar or crust/facet weak layers. These are now buried 1m or more. The surface hoar layer may be found in sheltered shady areas at and below treeline, while the crust/facet layer is expected to be more widespread but also more variable. Prior to the storm, reports suggested that the layer could be between 0 and 120cm deep depending on exposure to wind. The new storm load means these deep layers may be more reactive than prior to the storm.

Regions covered