Bollettino valanghe

Purcells

Dec 29 – 30, 2011Avalanche Canada
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Archiviato · scaduto 15 years ago

Pericolo valanghe

Sat
Sun
Alta quota
4 · Forte
Limite del bosco
4 · Forte
Sotto il limite
3 · Marcato
Apri la mappa completa

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely - Very Likely
    Dimensione
    1–4
    Predominantly on North through South East aspects, but some localized northerlies have formed wind slabs into unusual places. Stiff snow surfaces, cracking and hollow drum like sounds are signs of unstable snow.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible - Likely
    Dimensione
    2–6
    As the load increases the mid-December buried surface hoar layer may become reactive. The failure of this layer could initiate large, destructive avalanches.

  • Storm Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely - Very Likely
    Dimensione
    1–4
    Storm slabs can be destructive, run far and fast. The slabs are sitting on two weak layers in the upper 100cms of the snowpack. The weight of the slab may trigger the initial weakness, then step down to the deeper layer creating large avalanches.

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Friday: Snow amounts 5-10cms. Ridgetop winds 40km/hr from the West. Freezing levels could rise to 1200m. Saturday/Sunday: A ridge of high pressure is expected to move into the region for the weekend. Mainly sunny skies, and seasonal temperatures with a light-moderate NW flow.

Avalanche Summary

An operation in the North end of the region saw a natural avalanche cycle up to size 3.5 on Wednesday. Additionally naturals up to size 1.5 were reported in the Southern sections. There was also a skier remote avalanche that was triggered from 25m away. This failed on the December 24th surface hoar layer. Where this layer exists is quite touchy and has wide propagation propensity.

Snowpack Summary

The region has received up to 40cms of new snow since Christmas. New snow and consistent winds have deposited soft slabs onto leeward exposed slopes, and terrain features. This new snow has buried the December 24th surface hoar layer. I'm not sure how widespread this exists in the Purcells, but it also formed in adjacent regions which makes me suspicious. With additional load this layer may fail stepping down to the mid-December layer. There is about 60-80cms of snow sitting over the Mid-December interface of surface hoar and facets. Some observations suggest this layer is gaining strength, but still remains within the threshold of human triggering where there are sufficient load/slab properties. This will be the layer to watch as more snow and wind accumulates this week. Below this weak interface the mid pack is well-consolidated and strong. Near the base of the snowpack there are a few layers that have the potential to trigger with very heavy loads or from shallow spots. These include a surface hoar/crust/facet layer from early November, and the basal facets/depth hoar that are currently unreactive but still a concern in areas that have not previously avalanched.

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