Avalanche forecast

South Columbia

Apr 21 – 22, 2018Avalanche Canada
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Avalanche danger

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

New snow accumulations are likely to become increasingly reactive as warming and solar radiation increase over the day. Increase your caution around sun-exposed slopes as well as wind loaded areas.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    New snow and strong winds will have formed new wind slabs in the lee of wind-exposed terrain. Slabs are likely to remain reactive over the near term and reactivity is likely to increase with sunshine and daytime warming on Sunday.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3
    Large cornice failures have been reported in the past week and cornices will weaken with daytime warming on Sunday. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.

  • Loose Wet

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–1.5
    Daytime warming and sun exposure will promote natural loose wet avalanche activity on Sunday - especially around steep sun-exposed terrain.

Confidence

Moderate -

Weather Forecast

Sunday: A mix of sun and cloud. Light northwest winds. Freezing level to 1700 metres with alpine high temperatures around -5.Monday: Sunny. Light south winds. Freezing level to 2400 metres and climbing overnight. Alpine high temperatures around +1.Tuesday: Mainly sunny. Light south winds. Freezing level to 3000 metres with alpine high temperatures around +5.

Avalanche Summary

A few natural storm and wind slab releases were observed on Thursday, ranging from size 1-2.5. One of these was a size 2 slab triggered by a loose wet avalanche while the 2.5 wind slab was triggered by natural ice fall on a north aspect at 2200 metres. It featured a 45 cm crown fracture.Reports from Wednesday included an observation of a natural size 2 cornice release from a north aspect in the north of the region. Numerous natural loose wet avalanches were also observed on sun-exposed aspects in the Monashees.Tuesday's reports showed numerous small (size 1) storm slabs releasing both remotely and with ski cutting. Crown fractures were in the 35-40 cm range and activity was observed at all elevations and on all but west aspects.In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity.Looking forward, sunshine and warming temperatures are expected to promote both natural and human-triggered avalanches limited to the new snow. The same warming may also cause natural cornice collapses.

Snowpack Summary

About 15-20 cm of new snow has accumulated above a melt freeze crust found on the previous surface on all but north aspects above about 2200 metres. Below it, About 70-100 cm of rapidly settling storm snow overlies another supportive crust which shares similar distribution to the upper crust.Within the upper snowpack there are now a few different crusts with the shallowest of these (down 30-50 cm) now a limited concern as warm temperatures have promoted settlement and bonding in the upper snowpack.With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains some lingering concern around the mid-March persistent weak layer in the alpine where it is found 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but is likely trending towards dormancy. It should be kept in the back of our minds for its capability to produce large avalanches should it be triggered with a heavy load such as a snowmobile or cornice collapse.Deeper persistent weak layers from December and January are considered dormant at this time.

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