Avalanche forecast

Purcells

Feb 28 – 29, 2012Avalanche Canada
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Avalanche danger

Thu
Fri
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
    Winds are forecasted to be out of the SW with enough velocity to form wind slabs Wednesday. Fresh wind slabs will likely be touchy in wind exposed areas. Stay alert for changing conditions.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–7
    40 -100 cm of storm snow is settling into a cohesive slab above a very sensitive surface hoar layer. I still expect to see some natural avalanche activity on Wednesday.

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–3
    Loose dry storm snow is sliding easily and running fast on the old surface. The 5 - 10 cm of snow forecasted for Tuesday eve into Wednesday will only add to this problem.

Confidence

Good

Weather Forecast

A low pressure system is tracking just south of the international border Wednesday, and the Purcells will see 5 to 10 cm of snow from the system Wednesday. Alpine winds will be strong out of the SW, but will quickly diminish as you drop in elevation. Wed. 1500m Temp: H: -3, L: -11. On Thursday a weak ridge builds back into the region and no significant precip is expected for most of the region. The exception will be in the Panorama area where 5 cm are expected to fall from convective flurries. Thur. 1500m Temp: H: - 4, L: -10. The ridge flattens back out on Friday, opening the door to zonal flow for most of the province. A few cm are expected each day: Fri, Sat & Sun.

Avalanche Summary

Numerous Natural, Explosive Controlled, Skier Controlled and Skier Remote avalanches to size 2.5 were reported on all aspects and elevations Monday, the majority of which failed on the Feb. 08 Surface Hoar.

Snowpack Summary

20-25 cm of dry light snow rests above the recent stiff windslabs. The upper snowpack structure is very complex. There are buried layers of surface hoar, buried melt-freeze crusts, and some buried crusts with facets. These weak sliding layers are buried anywhere from 40 - 80 cm by several different storm layers. There are some shears in the storm layers on decomposed and fragmented snow crystals. As the snow above the surface hoar layers settles into a cohesive slab, we are seeing easier and more sudden shears that are a bit deeper. The surface hoar is more likely to produce wider propagations, and lower angle fractures in areas where it is associated with a crust. The crust has been reported to be 2-3 cm thick in some areas. The mid-pack is generally well settled. Basal facets have not been reactive, but operators continue to monitor this layer in tests. Triggering this deep persistent weak layer is unlikely, but shallow snowpack areas or shallow weak areas adjacent to deeper wind loaded slopes are the most suspect locations.

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