Avalanche forecast

South Rockies

Feb 12, 2019Avalanche Canada
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Archived · expired 8 years ago

Avalanche danger

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

The pieces are in place for a significant snowfall enhancement as the incoming storm collides with embedded arctic air. Avalanche danger will increase over the day as new snow accumulates and is affected by wind.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5
    New snow will add load to a weak layer of surface hoar already buried 35-45 cm deep. This layer has been reactive to human triggers, particularly in undisturbed areas. It is best preserved in shaded, sheltered areas between 1600-2200 m.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–2
    New snow will be accumulating Monday night and over the day on Tuesday. It has the potential to quickly form reactive storm slabs in areas affected by wind. Loose dry avalanches will be an increasing concern as snow accumulates in sheltered areas.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–3
    The bottom of the snowpack consists of weak and sugary faceted snow. The likelihood of triggering this layer may be relatively low, but the consequences remain high. Any deep persistent slab avalanche will be large and destructive.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Monday night: Increasing cloud with isolated flurries beginning with a trace of new snow. Light southwest winds, increasing to strong in the alpine.Tuesday: Cloudy with periods of snow bringing 20-30 cm of new snow, decreasing overnight. Light southwest winds, increasing to strong or extreme in the alpine. Alpine high temperatures around -11.Wednesday: A mix of sun and cloud with continuing isolated flurries and a trace of new snow. New snow totals up to 40 cm. Light west winds. Alpine high temperatures around -9.Thursday: Mainly cloudy with isolated flurries and a trace of new snow. Light southeast winds shifting to southwest in the evening. Alpine high temperatures around -7.

Avalanche Summary

A social media post from the Marten area of Elk Valley on Thursday describes touchy persistent slab conditions, with lots of smaller slabs releasing over the mid-January surface hoar layer. Check out the post here. Of note is the fact that this area was previously untracked, leaving the mid-January layer undisturbed. This is something to bear in mind as dry conditions persist and the motivation to step out of well-traveled terrain increases. Areas where this layer is undisturbed are far more likely to hold reactive persistent slabs.

Snowpack Summary

Forecast new snow will bury a variable surface of heavily wind affected old storm snow at alpine and wind-exposed treeline elevations, while adding to 25-35 cm of lower density storm snow from last week in sheltered areas above 1700 metres. In these sheltered areas, this older storm snow may cover a layer of weak, feathery surface hoar crystals. Below 1700 metres, the new snow will accumulate above a thinner cover (5-10 cm) of the same storm snow that instead overlies a melt-freeze crust.The mid-January layer of surface hoar or a crust is buried around 35 to 45 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. The melt-freeze crust is found on south aspects at all elevations. This layer was the subject of a recent Special Public Avalanche Warning.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains. The basal snowpack is becoming even weaker under prolonged cold temperatures, especially in thin snowpack areas.

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