Avalanche forecast

Purcells

Jan 23 – 24, 2015Avalanche Canada
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Archived · expired 12 years ago

Avalanche danger

Sun
Mon
Alpine
4 · High
Treeline
4 · High
Below
3 · Considerable
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Highlights

High danger expected for areas where rain/snow, warm temperatures and high winds come together. Some parts of this region may see less precipitation and the danger may be slightly too high for alpine areas.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    2–5
    A weak layer comprising of feathery surface hoar crystals and on south aspects a crust is buried between 25 and 50 cm below the surface. This layer was active during the last storm cycle and is likely to respond again to additional loading or warming

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–5
    New snow or rain with high winds and warm temperatures will release avalanches from sufficiently steep terrain in a number of places.

  • 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 warm, wet storm is expected to bring 10-15 mm snow/rain on Friday night to wetter areas, and a further 10 mm or so on Saturday. Freezing levels are expected to rise to around 2000 m on Saturday. Sunday: most likely a mix with rain likely in the west, and some clearing in the east. Freezing levels expected to remain very high at around 2500 m. On Monday, light rain, with freezing levels remaining high. Strong southwest Winds are expected throughout the period.

Avalanche Summary

Parts of this region that see good amounts of snow/rain with warm temperatures are likely to see an active avalanche cycle. Areas that stay dry may not see natural avalanches, but human-triggered avalanches will still be possible. Avalanches ran in the region during and after the last major storm, typically running on the mid-January surface hoar layer.

Snowpack Summary

Moist new snow and rain forecast for this weekend will fall on a moderately dense upper snowpack. A weak layer that comprises feathery surface hoar crystals lies buried between 25 and 50 cm below the surface. This "mid-January" weak layer has been responsible for most of the recent avalanche activity. While 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, I'd still bet on this layer being active during the forecast periods of warming and rain through the weekend.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