Avalanche forecast

South Coast

Dec 27 – 28, 2011Avalanche Canada
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Avalanche danger

Thu
Fri
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
    2–6
    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
    1–5
    Weaknesses may exist within or under the new storm snow. Natural avalanches will become more likely with each successive storm.

Confidence

Fair - Timing of incoming weather is uncertain

Weather Forecast

A steady stream of weather systems will continue to deliver moderate to heavy precipitation, strong winds, and fluctuating freezing levels. Tuesday night through Wednesday: 30-50cm of snow. Very strong SW-W winds. Freezing level (FL) rising to 1600m overnight. Thursday: Snow beginning later in the day; 15-20cm. Moderate to strong SW-SE winds. FL lowering to 1000-1200m. Friday: Drier during the day but could see another system arrive in the evening. FL around 1000-1200m.

Avalanche Summary

There is one new report of skier triggered slab avalanche from Monday. It was intentionally triggered on a steep northerly slope near treeline, and may have released on buried surface hoar. I expect the size and likelihood of natural and human triggered avalanches to increase with the next weather system arriving Tuesday night.

Snowpack Summary

Wind-exposed slopes are predominately scoured and pressed, with pockets of wind slab from 30 to 60cm deep 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. Generally speaking, confidence in this interface is growing, especially since it has'nt seen a significant load at the elevations where it exists. 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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