Avalanche forecast

South Coast

Mar 6, 2017Avalanche Canada
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Avalanche danger

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

There is a lot of uncertainty surrounding the buried weak layer underneath the persistent slab. This interface has remained problematic longer than we'd typically expect on the coast. Cautiously gather info before venturing beyond simple terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    2–3
    Storm snow from the last week has coalesced into a slab up to a meter in depth that is poorly bonded to the old surface due to a persistent buried weak layer. These slow to heal slabs are most likely to be triggered in wind exposed terrain.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2
    Watch for the development of fresh small storm slabs Monday if storm totals exceed 10cm.

Confidence

Moderate -

Weather Forecast

A cold broad upper trough will be the dominant weather feature over southwestern BC for the forecast period. This feature is expected to keep freezing levels around 500m and should deliver consistent snow showers through the first half of the workweek.MONDAY: Overcast skies, freezing level around 500m, moderate SW wind, 5 to 10cm of snow. TUESDAY: Overcast skies, freezing level around 500m, moderate to strong SW wind, 5 to 15cm of snow. WEDNESDAY: Overcast skies, freezing level around 500m, moderate SW wind, 1 to 5cm of snow. Visit avalanche.ca/weather for a more detailed mountain weather forecast.

Avalanche Summary

There were two significant avalanche accidents on the South Coast Saturday. Sadly, there was an avalanche fatality west of Whistler near Gin Peak/Hanging Lake. This avalanche occurred on a west-facing feature at treeline, size is estimated to be 2 to 2.5, approximately 80m wide with a 100cm crown. At this time it is not clear what interface the avalanche failed on. We're still short on details, but there is a bit more information on our website: https://bit.ly/2m9xtsm as well as the South Coast Touring FB page: https://bit.ly/2m9liMjThe second incident occurred in the South Coast region where one person was reported to be fully buried in a feature called the Tony Baker Gully near Cypress Mountain. North Shore SAR removed the person from the scene with reportedly serious injuries.Previous to this a natural avalanche cycle occurred on March 3rd which mainly involved storm slabs up to 60cm in depth, but a persistent slab running on the mid-February crust was also observed.

Snowpack Summary

Over the weekend strong winds out of the south/southwest formed fresh wind slabs with the 75 to 170cm of snow that has fallen in the last week. Recent observations suggest this slab ranges from 20 to 100cm in depth throughout the region, but it could easily be twice that deep on lee features at and above treeline. We usually see rapid settlement and bonding on the coast, but this slab is still bonding poorly to the the late February persistent weak layer that is composed of a sun crust on southerly aspects, and surface hoar on shaded aspects. Below this interface is the mid-February crust which was active in a natural avalanche cycle on March 3rd. This crust has been reported to have facets above it.  It should be easy to find and test in your profiles, look for it around 75 to 125cm below the surface.. The mid and lower snowpack appear to be well settled and strong.

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