Avalanche forecast

Purcells

Feb 20 – 21, 2016Avalanche Canada
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Avalanche danger

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

Sunny skies forecast for Sunday. Strong solar radiation may result in increased avalanche activity. Storm slabs and persistent weak slabs may be easier to trigger with light loads.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    Natural cornice falls may trigger storm slab avalanches on the slopes below. Strong solar radiation may increase the likelihood of natural cornice falls.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    There may be weak layers within the recent storm snow, or the entire storm slab may release on the melt-freeze crust that formed last week. Strong solar radiation may weaken the storm slab bond and increase the likelihood of triggering an avalanche.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    3–5
    The early January surface hoar may continue to be triggered by large loads like storm snow avalanches in motion, or light loads in shallow or weak spots on large terrain features. This problem is more likely in the north of the region near Golden.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Sunday

Weather Forecast

Mostly clear overnight with light westerly winds and freezing down to valley bottoms. Mostly clear on Sunday with cloud developing in the late afternoon. Light southwest winds and freezing levels climbing up to 1200 metres. Light snow starting overnight and continuing on Monday with moderate westerly winds and daytime freezing levels climbing from valley bottoms up to 1200 metres. Clear on Tuesday as the ridge re-develops, temperatures around -12 at treeline overnight.

Avalanche Summary

We have a report of a large size 3.0 avalanche on a west aspect in the Quartz creek area. We have limited information at this time, but it sounds like people were involved and that there was one fatality. We will provide more information when available. Natural wind slab avalanches up to size 2.0 were reported on Friday, as well as skier accidental storm slabs to size 1.5. On Thursday we had reports of natural storm slab avalanches up to size 2.0 and explosives controlled avalanches up to size 2.5. On Wednesday there were reports of natural cornice falls up to size 2.5, and explosives control released slab avalanches up to size 2.5. Most of the slab avalanches were in the alpine on east aspects.

Snowpack Summary

There has been 20-30 cm of new snow in the past few days that has added to the recent storm slab above the buried crust. About 30-60 cm below the surface, you'll likely find a melt freeze crust which exists in most places except for in high elevation shaded terrain. In general there seems to be a reasonable bond between the crust and the overlying snow. I'd still keep an eye on this interface as it has become reactive on some features. If the sun comes out this weekend, periods of strong solar radiation may increase the likelihood of triggering the storm slab. In isolated areas there may be a weak layer of surface hoar at the storm snow/crust interface that is touchy to human triggers and may result in wide propagations. The early January surface hoar/ facet layer is typically down 70-120 cm. Avalanche activity at this interface has tapered-off over the past week, but I'd be reluctant to trust this potentially destructive layer just yet. In general, the lower snowpack is well settled and strong, apart from some thin snowpack areas where basal facets exist.

Regions covered