Avalanche forecast

Purcells

Jan 22 – 23, 2015Avalanche Canada
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Archived · expired 12 years ago

Avalanche danger

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

Avalanche danger (and riding quality) is likely to deteriorate with forecast warm temperatures and rain this weekend.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    A weak layer comprising of feathery surface hoar crystals and on south aspects a crust is buried between 25 and 45 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

Fair - Intensity of incoming weather systems is uncertain

Weather Forecast

A succession of storms progressively get stronger and warmer through the weekend.  Friday: flurries in the afternoon. Freezing levels 1000 m in the morning, climbing rapidly towards 2000 m in the afternoon. Ridgetop winds 30-40 km/h from the southwest.  Saturday: Rain to all but the highest areas. 5-10 mm is the best current estimate. Freezing levels around 2400 m. Strong southwesterly winds.  Sunday: Light rain. Models currently indicate around 5 mm. Freezing levels around 2500 m. Strong southwesterly winds.

Avalanche Summary

Avalanches up to size 2 were reported to have run during and immediately after the most recent storm on all aspects and at elevations from 1800-2300 m. Most avalanches were running on the most recent layer of surface hoar, with typical crown depths of 30-60 cm. There was one report of an avalanche on the more deeply buried mid-December weak layer, although it appears as though it may have been triggered in a shallow spot, as the crown depth was reported to be only 30-45 cm.

Snowpack Summary

Between 15cm and 40cm of recent snowfall fell during the last major storm last weekend. Wind slab deposits have been consistently reported in alpine areas. This new snow buried a prominent layer of surface hoar, which sits above a sun crust on steep sun-exposed slopes. This "mid-January" weak layer has been responsible for most of the recent avalanche activity. Reports do indicate that this layer is starting to gain some strength in this region, becoming more difficult to trigger when ski-cutting small slopes.The mid-December surface hoar/crust layer is typically down 60-120cm below the surface. The reactivity of this persistent weak layer appears to be quite variable but the potential still exists for large, destructive avalanches in some areas. The layer appears to be the most reactive at and below treeline. The mid-Nov weak layer comprising facets can still be found near the bottom of the snowpack but has generally become inactive.

Regions covered