Avalanche forecast

South Coast

Dec 28 – 29, 2011Avalanche Canada
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Avalanche danger

Fri
Sat
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely - Certain
    Size
    2–7
    Wind slabs have developed in exposed lee and cross-loaded terrain and may be quite reactive, especially where they over-ride last weekends rain crust or weak facets (sugar snow) from the early December dry spell.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–6
    Weaknesses may exist within or under the new storm snow. Natural avalanches will become more likely with each successive storm.

Confidence

Poor - Timing of incoming weather is uncertain

Weather Forecast

Wednesday night and Thursday: Another system arrives bringing 20-30cm of snow. The freezing level should start at around 1200m and lower to 800m on Thursday. Winds are strong from the W-SW. Thursday afternoon should be a little drier before another system arrives overnight. Friday: 15-25cm of snow. Continued strong SW winds. Freezing level 1000m. Saturday: Drier for the first half of the day as a brief ridge of high pressure builds, but should see some precipitation in the afternoon as another frontal system is on the way. Freezing level starting at 600-800m, rising with the warm front. Low confidence for Saturday.

Avalanche Summary

Observations are limited, but there are reports of a small natural avalanche cycle up to Size 2 on Tuesday. The size and likelihood of natural and human triggered avalanches should continue to increase heading into the weekend.

Snowpack Summary

Southern areas received up to 40cm of new snow (above 1700m) with the last system, while northern areas had 20-30cm. Wind-exposed slopes are predominately scoured and pressed, with deep and dense wind slabs on North to East aspects at treeline and in the alpine. This new storm snow overlies a weak rain crust that formed last weekend. This crust extends to treeline elevations and overlies buried surface hoar and/or facets 10cm below. In the alpine where the crust does not exist, a stiffer wind slab may over-ride surface facets that formed during the early December dry spell. Persistent weaknesses seem to be less of a concern in the Cascades (Coquihalla and Allison Pass).The mid and lower snowpack are generally well-settled and strong.

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