Avalanche forecast

Purcells

Mar 3 – 4, 2012Avalanche Canada
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Avalanche danger

Mon
Tue
Alpine
4 · High
Treeline
3 · Considerable
Below
3 · Considerable
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Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–5
    Generally lurking below ridgecrests, behind terrain breaks, and in gullies. Fresh wind slabs are expected to be very touchy and continued strong winds over the forecast period is expected to overload weaknesses.

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–3
    Conditions continue to be prime for cornice growth & ultimately, cornice failure. Falling chunks of cornice have the potential to initiate wind slab avalanches.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–6
    Persistently weak buried surface hoar demands continued diligence and conservative decisions. The potential for remote triggering, step down avalanches, and wide propagations, makes this weakness particularly tricky to predict.

Confidence

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

Weather Forecast

An "almost pineapple" weather pattern is setup across the province directing the firehose at the neighboring regions to the north & west, directing a more modest amount over the Purcells. SUN: FZLVL stays near 1300m. Elevations above the freezing level should see 4 - 8 cm in the afternoon. Ridgetop winds are expected to be Strong out of the West. MON: FRLVL lowers to 900m. 5 -10 cm of snow expected above 900m. Winds 10 - 15cm of snow is expected above 1200m, light rain below. Ridgetop winds remain strong out of the W/SW. Tue: A ridge of high pressure slides into the region bringing more seasonal cool temperatures, high solar & light winds.

Avalanche Summary

No new avalanches to report from the Purcells but, visibility was super limited Saturday by all accounts.

Snowpack Summary

A cohesive slab continues to settle over the mid-February surface hoar, which is generally down in the 40-55cm range. Recent reports include whumpfing and cracking, and moderate but sudden compression test results. This persistent weakness is susceptible to remote triggering and has the ability to propagate in low angled terrain, and the overlying slab structure creates the potential for step-down avalanches. Basal facets have only been reactive on steep, shallow, and rocky slopes, 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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