Avalanche forecast

Purcells

Mar 6 – 7, 2016Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Storm slabs continue to be a concern. Wide fracture propagations are possible where the storm snow is sitting on a weak buried layer of surface hoar.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    New wind slabs have developed in the alpine and at treeline due to strong southerly winds and warm temperatures. Wind slabs may be sitting on the buried surface hoar layer from February 27th.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    1–4
    New cornice growth may be large and fragile. Avoid slopes beneath cornices.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely - Possible
    Size
    2–5
    Persistent weak layers of buried surface hoar may continue to be triggered by large loads like cornice falls or a large group of sledders re-grouping. Avoid un-supported terrain and shallow wind effected slopes adjacent to large alpine slopes.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

Freezing level dropping down close to valley bottoms overnight with continued light precipitation. Light precipitation and cloudy skies on Monday combined with light southerly winds and freezing levels climbing up to about 1700 metres. A spring diurnal freeze/thaw cycle setting up for Tuesday and Wednesday with freezing levels dropping to valley bottoms overnight and then rising up to 1500 metres during the day. The next major storm pulse developing on Wednesday night.

Avalanche Summary

Natural wind slabs and storm slabs up to size 2.5 were reported on Saturday. Natural and explosives controlled avalanches up to size 2.5 were reported on Friday. One size 3.0 avalanche released sympathetically to a cornice falling 100 metres away. No new natural avalanches reported on Thursday. One skier remote size 2.0 storm slab avalanche was reported from an east aspect in the alpine.

Snowpack Summary

Strong southerly winds have developed wind slabs in the alpine and at treeline. The 20-40 cm of recent storm snow is bonding poorly to a melt-freeze crust on previously sun-exposed slopes and lower elevation terrain, and/or a layer of surface hoar on shady and sheltered slopes at treeline elevations. The surface hoar and/or crust layer buried in mid-February is now down 50-80cm. This layer was less reactive over the past week with cooler temperatures. Large weak cornices remain concerning and have recently triggered persistent slabs on slopes below. The early January surface hoar/facet layer is typically down 70-120cm. Triggering an avalanche on this layer has become unlikely but it still has isolated potential to produce very large avalanches with a heavy trigger. In general, the lower snowpack is well settled and strong, apart from some thin snowpack areas where basal facets exist.

Regions covered