Avalanche forecast

Cariboos

Dec 19 – 20, 2011Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–4
    Wind slab development on lee and cross-loaded features. Anticipate loading lower on the slope with forecast high winds. These wind slabs may be sliding easily on the early December surface hoar/facet/crust layer.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    The recent storm snow may settle into a cohesive slab above the early December surface hoar/facet/crust layer. This weakness is touchy to rider triggers and may produce wide propagations in protected terrain features.

Confidence

Fair - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

10-20cms expected overnight Monday through Tuesday. Strong westerly winds switching from the northwest in the afternoon . Freezing levels could rise to 1200m then falling back down to valley bottom. A ridge of high pressure over the interior on Wednesday will bring mainly dryer conditions. Winds will be moderate from the northwest, and teeline temperatures could dip to -13.

Avalanche Summary

Numerous natural avalanches up to size 2.5 occurred in the Cariboos on Sunday. They ran on all aspects above 1800m. Most of this avalanche activity has occurred on the early December surface hoar/facet/crust layer.

Snowpack Summary

Some areas of the North Columbia (Cariboos) received up to 30 cm on Saturday then another 5-10cm overnight Sunday. The North and West Monashees received an additional 20 cm on Saturday night. Strong southwest winds and warm temperatures have created wind slabs on North through East aspects in the alpine and at treeline. The storm slab sits between 50-80 cms and has been been naturally reactive. This layer is very touchy and rider triggers are likely. The East and South ranges of the North Columbias have been much drier. The new snow load continues to build faster in the northern ranges than in the southern and eastern ranges. The depth of the new storm snow above the various old surfaces is what is driving the danger ratings at this time. Large surface hoar and near surface facets are widespread above various crusts and hard wind slabs. Some areas have a sun crust in the alpine on steep south and west aspects. There is a rain crust that is buried between 40-55 cm in some areas that reaches up to about 2200 metres. The mid-pack is reported as generally strong and well settled. Observers are still able to find the early November surface hoar layer that sits around 120-150cms down. This layer has not been reactive during the recent long dry spell. Tests show that it is getting harder to pull the snowpack apart at this interface. We may still see this layer become active again if we get the right combination of load and warm temperatures. The midpack is well settled. Going down deeper sits the interface between the snow that did not melt over the summer, the glacial ice, and the October rain event. At this point the interface remains dormant.

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