Avalanche forecast

Purcells

Jan 5 – 6, 2012Avalanche Canada
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Avalanche danger

Sat
Sun
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    In the alpine and at treeline winds continue to redistribute storm snow into wind slabs. The winds have been randy; I'd be suspect of any open area even below treeline. Wind slabs may be stiff, and have a hollow drum like sound beneath you.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–7
    A cohesive slab sits over a surface hoar weakness buried in mid-December. This layer is still touchy and susceptible to rider triggers. Avalanches on this layer will be large, destructive and may fracture across surprisingly far distances.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    Storm slabs have been building in the past 48hrs over the January 03 buried surface hoar layer. In some locations up to 50cms has fallen. These slabs are likely touchy. They can run far, fast and be destructive.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain on Sunday

Weather Forecast

The next couple days brings cooler temperatures and dryer conditions. Friday: Mix of sun and cloud in the afternoon. Light snow amounts near 5cms. Ridgetop winds 20-30km/hr from the SW. Alpine temperatures near -9. Freezing levels at valley bottom. Saturday: A Northerly flow brings mainly sunny skies with seasonal conditions. Ridgetop winds 15-20km/hr from the NW. Treeline temperatures near -9. Sunday: Light to moderate precipitation is expected accompanied by strong SW winds. Freezing levels may rise to 1300m in the Northern part of the region, and 2000m in Southern locations by the afternoon.

Avalanche Summary

One large natural slab avalanche was reported. This was a size 2.5 that occurred on a East aspect, at 2500m. The crown was 100cms in depth, 100m wide, and ran 200m down slope. Natural activity has tapered off, I'd still be suspicious of the mid-December layer susceptible to rider triggers (especially sledders) creating large avalanches. Please don't rule this out yet.

Snowpack Summary

Some locations in the region has received up to 50cms in the past 48hrs. In the alpine and at treeline this new snow is being blown onto lee slopes and terrain features adding to previous soft slabs and wind slabs. In sheltered locations this new snow buries the surface hoar that formed over the New Years. We'll date this the January 3 SH layer, the crystals reported to be up to 10mm. This may become a concern with increased load as it reaches it's threshold. Some locations in the region received some rain up to 2000m, but consistent rain to 1500m. This may have solved our lower elevation New Years surface hoar layer. Below the surface down 80-140cms lurks the mid-December surface hoar/ crust/ facet layer. This is a layer of concern. Test results on this are still variable in the moderate to hard ranges with sudden planar characteristics. It continues to be sensitive to large triggers like cornice fall and explosives. Between this layer and the bottom of the snowpack sits a well settled mid pack. At the bottom of the snowpack basal facets and depth hoar crystals live. These become a concern in thinner snowpack areas, and became reactive under the new load of the post-Christmas storms.

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