Avalanche forecast

Purcells

Mar 17 – 18, 2019Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

Overhead hazards, such as large avalanche paths and cornices will be a major concern over the next few days. Sporadic, very large natural avalanches may run full path to valley bottoms. Avoid all avalanche terrain during periods of rapid warming.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1.5–3
    Sunshine and rising freezing levels will elevate the potential for cornice failures resulting in large avalanches.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1.5–2.5
    Warming temperatures have settled the recent storm snow into a cohesive slab sitting on weak facets (sugary snow) that is ripe for human triggers; especially at treeline and above.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Pin-wheeling snow below cliffs is a common sign that loose wet avalanches are becoming more likely.

Confidence

Moderate -

Weather Forecast

SUNDAY NIGHT: Clear / Light, northeasterly winds / Alpine low -2 / Freezing level 1500 m.NOTE: Sunday night is the last night of the forecast period that freezing levels are expected to drop at night. This will significantly increase the impact of day time warming on the snowpack.MONDAY: Sunny / Light, northeasterly winds / Alpine high 4 / Freezing level rising to 2700 m.TUESDAY: Sunny / Light, southeasterly winds / Alpine high 6 / Freezing level rising to 3000 m.WEDNESDAY: Sunny / Light, southeasterly winds / Alpine high 7 / Freezing level 3000 m.

Avalanche Summary

On Saturday, several naturally triggered, persistent slab avalanches up to size 3 were reported on a variety of aspects in the alpine. Natural avalanche activity and size of avalanches are expected to increase during the next few days.On Friday, a natural size 2.5 and explosive triggered size 3 persistent slab avalanches were reported on north aspects in the alpine. Human triggered persistent slab avalanche activity is expected to increase with the forecast sunshine and rising freezing levels.

Snowpack Summary

15-30 cm of recent storm snow is sitting on a pile of facets (sugary snow), as well as a crust on sun exposed slopes. The recent storm snow has settled into a cohesive slab and is ripe for human triggering. This persistent slab is currently our primary concern.At lower elevations a weak layer of surface hoar (weak, feathery crystals) buried in mid-January can be found approximately 50-90 cm deep and may be combined with a crust on south facing slopes. This layer has recently been unreactive, however, the forecast warming event may awaken this layer in low elevation areas such as steep cutblocks and large open glades.The base of the snowpack is composed of facets (weak, sugary snow) that sit on a crust. Very large avalanches failing on this persistent weak layer will become more likely with the forecast sunshine and rising freezing levels.

Regions covered