Avalanche forecast

Purcells

Apr 17 – 18, 2012Avalanche Canada
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Archived · expired 14 years ago

Avalanche danger

Thu
Fri
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
3 · Considerable
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Avalanche problems

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–5
    Loose wet snow avalanches are expected during periods of daytime warming or if periods of rain showers persist. Loose snow avalanches may entrain a great deal of mass and may trigger deep weak layers.

  • Wet Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–6
    Wet slab avalanches may be triggered during periods of daytime warming or when there is no overnight freeze. Wide propagations are possible on the buried March crust.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–7
    Avalanches may release on the deeply buried weak layers from February or from depth hoar that has developed during the winter. The likelihood will increase if warm temperatures persist and there is no overnight freeze.

Weather Forecast

Gusty westerly winds are expected to develop overnight and rain showers and flurries should start by mid-day and continue into Wednesday night. Thursday is forecast to be unsettled with gusty southwest winds and periods of rain showers and flurries at higher elevations. The next Pacific frontal system is forecast to move into the interior by early Friday morning. Expect 5-10 mm of precipitation combined with overnight freezing levels down to about 1500 metres.

Confidence

Fair - Due to limited field observations for the entire period

Avalanche Summary

Spring conditions exist in the region. Exposure to the sun, warm temperatures, and periods of rain are the most likely factors to influence the avalanche danger. If the temperatures go below freezing overnight, strong crusts should develop that are likely to hold the snowpack together. If the sun shines for a few hours, the crusts may break down quickly and moist surface snow avalanches may start running naturally. Continued warming from more sun, rain, or no overnight freeze, may cause surface avalanches to step down and trigger deeper wet slab avalanches. Prolonged warming may cause very deep releases on weak layers that were deposited early in the season, or on depth hoar that developed during the winter. It is important to monitor the temperature and the freezing levels as they may change rapidly from day to day.

Snowpack Summary

As we transition into spring the surface layers have a great deal of influence on the snowpack. When there is a solid re-frozen surface crust, travel is fast and easy, and the snowpack is held together by the surface cap. Any deeper persistent weak layers are unlikely to fail until the surface cap breaks down from daytime heating. When there is no crust, any deeper weak layers may fail depending on the amount of heat and the triggering force that is applied. If it cools off and snows, new snow and windslabs may not bond well to the hard spring crusts.

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