Avalanche forecast

South Columbia

Jan 20 – 21, 2015Avalanche Canada
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Avalanche danger

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

Safe backcountry travel requires caution and good terrain selection at this time. Avalanches have been easily triggered by light loads.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–3
    Strong recent winds have set up dense pockets of wind slab in exposed lee terrain.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    A weak layer comprising of feathery surface hoar crystals and on south aspects a crust is buried between 30 and 50 cm below the surface. This layer appears to be widely found in this region and many recent avalanches were triggered on it.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–5
    A weak layer buried mid-December is still producing dangerous avalanches over a month after it was first buried. Particularly for slopes around treeline, there is a danger for a small avalanche to step down to this layer increasing the consequences.

Confidence

Good

Weather Forecast

Wednesday: Dry. Freezing level around 1000 m. Ridgetop winds 30-40 km/h from the southwest.  Thursday: Light flurries. Freezing level around 1500 m, although local areas, especially in the north of the region, could see higher freezing levels with pockets of warm air. Ridgetop winds around 30 km/h from the southwest.  Friday: At present this region looks like it will stay mostly dry, but models are uncertain with an approaching storm that could bring some snow and/or rain to this region. Strong southwest winds and rising freezing levels likely.

Avalanche Summary

Numerous avalanches were reported to have run during and immediately after the most recent storm. While most avalanches were in the size 1.5 to 2 range and ran on mostly north as east aspects from 1300 m to 2300 m, there were some larger avalanches that initiated in alpine start zones that were reported as size 3 avalanches. In at least one case, an avalanche stepped down to the mid-December weak layer.

Snowpack Summary

Between 30 and 50cm of new snow has fallen since Friday night, and has been distributed by strong winds into deeper, more cohesive deposits in higher wind-exposed terrain. The new snow overlies widespread 10-30mm surface hoar and a sun crust on steep sun-exposed slopes. I would expect continued touchy conditions, especially in areas where the recent snowfall exists as a cohesive slab.The still problematic mid-December surface hoar/crust layer is typically down 90-130cm below the surface. The reactivity of this persistent weak layer appears to be quite variable but still has the potential for large, destructive avalanches in some areas. The layer appears to be the most reactive in the south of the region at and below treeline. In these locations the surface hoar is more likely to sit directly above a hard crust.

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