Avalanche forecast

Purcells

Mar 4 – 5, 2012Avalanche Canada
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Archived · expired 15 years ago

Avalanche danger

Tue
Wed
Alpine
4 · High
Treeline
4 · High
Below
4 · High
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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 may overload buried weaknesses.

  • 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.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely - Very Likely
    Size
    1–4
    20cm has fallen as of Sun. eve and I expect an additional 15 -25 cm by Tues AM. Storm slabs will be sensitive Monday & will also add fuel to the wind slab problem. Don't let your lust for pow riding lure you into a dangerous situation.

Confidence

Fair - Intensity of incoming weather is uncertain

Weather Forecast

The Purcells do quite well with regard to snowfall for the next few days. The region should pick up 4 – 8cm Sunday evening and an additional 3 – 5cm Sunday night. MON: A surface low develops over the Southern Interior Monday which should bring an additional 10 – 15 cm. TUE: High pressure builds in Tuesday which should result in quite a bit of solar & cooler (seasonal) temps. Winds increase late in the day out of the W/NW near ridgetop. WED: The pattern looks very similar to last week. Freezing levels should be on the rise, but, a ridge of high pressure off the coast of California is shielding the region from moisture.FZLVL:Mon: 500m, lowering to the surface by evening.Tue: SurfaceWed: Starting near the surface, rising as high as 1700 in the afternoon.Wind: Mon: L SW, switching NW late in the day with frontal passage. Strong to Extreme W at ridgetopTue: L, NE at all elevations.Wed: Mod W/NW ridgetop winds strong NW.

Avalanche Summary

Control work in the Dogtooth range produced numerous slab avalanches to size 1, crowns 5 - 20cm in depth. With all the new snow & wind I suspect there was some natural activity, although we probably won't know the extent of it until skies clear Tuesday. There are two great observations from professionals working in the region recently. The first one can be found on the MCR, it talks about the widespread & sensitive nature of the SH in the Northern Purcells. You can start here and work your way into the March observations:https://www.acmg.ca/mcr/archives.aspThe other is in the form of a youtube video which also deals with the surface hoar, highlighting the potential for remote triggering and large propagations when this layer fails. Check out the shooting cracks in the video. Wild!:https://www.youtube.com/watch?v=UmSJkS3SSbA&feature=youtu.be

Snowpack Summary

A cohesive slab continues to settle over the mid-February surface hoar, which is generally down in the 65-75cm 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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