Avalanche forecast

Purcells

Apr 2 – 3, 2016Avalanche Canada
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Avalanche danger

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

A Special Public Avalanche Warning remains in effect Sunday. The freezing level remains quite high (2600 m) which will keep danger ratings elevated.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    3–6
    Continued high freezing levels and warm daytime temperatures Sunday are very likely to result in natural cornice failure. Large cornice falls may trigger buried weak layers resulting in very large avalanches.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    Continued warm weather may add enough heat to the snowpack to wake-up deeply buried persistent weak layers resulting in very large and destructive avalanches which have the potential to run full path.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Very Likely
    Size
    1–4
    Forecast high freezing levels and very warm daytime temperatures may break down surface crusts early and result in loose wet avalanches from steep solar aspects. Wet slab avalanches are possible if loose snow propagates on a buried crust.

Confidence

Moderate - Freezing levels are uncertain on Monday

Weather Forecast

Temperatures are expected to remain warm Sunday before beginning to cool Monday as a weak Pacific front injects cooler and cloudier marine air into the region. SUNDAY: Freezing level starting near 2400 m, climbing to 2600 m, light west/southwest wind, no significant precipitation expected, increasing cloud cover throughout the day. MONDAY: Freezing level beginning near 2500 m, lowering throughout the day to around 1900 m by sunset, light to moderate southwest winds, 2 to 6 mm of precipitation expected, overcast skies. TUESDAY: Freezing level beginning near 1500 m rising to around 2000 m, broken cloud cover, light to moderate wind generally out of the west, isolated convective snow/rain flurries/showers possible. For more detailed mountain weather information visit avalanche.ca/weather

Avalanche Summary

Lot's of activity to report from Friday.  Wet loose and wet slab avalanches failed naturally resulting in avalanches to size 3.  Glide crack failures to size 3 were also observed.  Loose wet avalanches to size 2 running on the ground were reported from the south of the region.  On Thursday, solar radiation continued to result in natural cornice falls up to size 2.5 and loose wet avalanches up to size 2.0. On Wednesday, slab and loose snow avalanches were reported up to size 2 on a variety of aspects, mostly triggered by cornices or solar radiation. On Tuesday numerous loose wet avalanches up to size 2.0 were reported, and one of these loose wet slides stepped down to a buried crust down 50 cm and resulted in a size 2.5 on a steep east aspect at 2200 metres.

Snowpack Summary

Ongoing warm daytime temperatures combined with mild nights continue to destabilized the upper snowpack.  On Sunday, any surface crust is expected to break down early, and persistent weak layers may fail if the warming reaches their fragile structure. The late February surface hoar/crust layer is down 40-90 cm. This layer may continue to react to human triggers during high daytime temperatures. Loose wet avalanches in motion, or cornice failure could result in an avalanche that steps down to deeply buried weak layers. Cornices continue to be described as large and fragile, and may fail with continued warming. Conservative terrain without overhead hazard is a good strategy for avoiding the persistent slab problem.

Regions covered