Avalanche forecast

Purcells

Dec 23 – 24, 2013Avalanche Canada
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Avalanche danger

Wed
Thu
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Highlights

The snowpack structure is complex and varies throughout the region. A conservative approach is essential.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–4
    New snow and wind will likely build touchy wind slabs over the old dense wind slabs. Rider triggering is likely and a small wind slab release may be enough to trigger a deep weak layer, producing a large-very large avalanche.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–5
    May be stubborn to trigger, especially in deeper snowpack areas. The sensitivity to triggers will likely increase in shallow locations, especially on steep, convex, north-facing slopes. If triggered, consequences can be devastating.

Confidence

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

Weather Forecast

A ridge of high pressure will set up over the Interior bringing a dry, cool northwest flow Tuesday-Wednesday. The next system should arrive Wednesday night bringing snow, wind and warming. Generally, the pattern is repeating itself. Tuesday: Cloudy with sunny breaks. Alpine temperatures -13. Ridgetop winds moderate gusting strong from the West.Wednesday: Snow amounts up to 10 cm. Alpine temperatures -5. Ridgetop winds moderate-strong from the West. Thursday: Cloudy. Alpine temperatures -5. Ridgetop winds light from the SW.

Avalanche Summary

On Sunday, one large size 2.5 natural slab avalanche occurred from a South aspect around 2650 m, this was said to have most likely run on a crust buried down 75 cm on a 40 degree slope. A couple of operators were out doing explosives avalanche control and triggered several large size 2-3 slab avalanches from NE-E aspects . Some of those ran on the deep persistent crust layer, and some were within the storm snow.

Snowpack Summary

Low density new snow covers stiff, dense wind slabs in exposed lee terrain at and above treeline. Average snowpack depths at treeline elevations are 100-130 cm. In the upper 80 cm of the snowpack a couple persistent weak layers exist, comprising of surface hoar and a facet/ crust combo. This interface has produced variable results with snowpack tests, and operators are keeping a close eye on them as the load above increases and/or a slab develops.A bigger concern, especially in the Northern part of the region where the snowpack is thinner and more variable is weak faceted and depth hoar crystals combined with a crust from early October. This is now down around 80-120 cm. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on steep, convex, north-facing slopes.

Regions covered