Avalanche forecast

South Columbia

Jan 22 – 23, 2015Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

A warm storm is approaching for the weekend that is likely to drop rain onto an already weak snowpack. Eeek!

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–5
    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
    2–5
    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

Fair - Intensity of incoming weather systems is uncertain on Saturday

Weather Forecast

A succession of storms progressively get stronger and warmer through the weekend.  Friday: Light rain or snow becoming heavier in the afternoon. Daytime amounts around 3-5 mm, with a further 10-15 mm likely overnight. Freezing levels 1000 m in the morning, climbing rapidly towards 2000 m in the afternoon. Ridgetop winds 40-60 km/h from the southwest.  Saturday: Rain to all but the highest areas. 10-15 mm is the best current estimate. Freezing levels around 2300 m. Strong southwesterly winds.  Sunday: More rain. Models currently indicate 15-25 mm. Freezing levels around 2500 m. Strong southwesterly winds.

Avalanche Summary

On Tuesday, which was after the storm had ended, there were a number of natural and human-triggered avalanches reported up to size 3. In some places the natural avalanches were thought to have been triggered as the sun started to shine. During the storm, avalanches up to size 3.5 were reported on a variety of aspects and elevations, most running on the most recent mid-January surface hoar layer. At least one avalanche in this region was reported to have stepped down to the mid-December layer.

Snowpack Summary

Between 30 and 50cm of new snow fell last weekend that was initially distributed into wind slab deposits. Since then, warm temperatures have settled the upper snowpack into a moderately dense slab. The new snow overlies a layer of surface hoar which may sit on top of a crust, particularly on sunny aspects. This "mid-January" weak layer is widespread and has been the main focus for most of the recent avalanche activity. It has also been consistently producing easy "pop" type failures in snowpack tests.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 the potential for large, destructive avalanches still exists in some areas, particularly in the 1600-1900 m elevation band. The layer appears to be the most reactive in the south of the region and in zones where the surface hoar was observed to sit directly above a hard crust.

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