Avalanche forecast

Purcells

Mar 22 – 23, 2016Avalanche Canada
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Archived · expired 11 years ago

Avalanche danger

Thu
Fri
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
1 · Low

Highlights

These danger ratings are for the north of the region where triggering the buried persistent weak layer continues to be a concern. Danger may be lower in areas that do not have this problem.

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    3–5
    Cloud cover and reduced solar may reduce likelihood, but forecast new snow and wind may increase the load on fragile cornice structures. Avoid slopes below cornices and chutes with corniced entrances.
  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    3–6
    The late February persistent weak layer has been remotely triggered as recently as Monday March 21st on a southeast aspect in the alpine. This problem may be more likely in the north of the region.
  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–3
    Forecast new snow and wind are expected to develop new storm slabs at all elevations. New snow may release as loose wet avalanches due to daytime heating.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Overcast with flurries, light southwest winds, and freezing levels down to 1000 metres overnight. Light snow with increasing southwest winds on Wednesday and daytime freezing levels up to 1600 metres. Light to moderate precipitation starting early Thursday with moderate to strong southwest winds and overnight freezing levels around 1300 metres. Freezing dropping back to valley bottoms by Friday morning. A weak ridge is expected to build on Friday, but we are un-certain regarding the amount of sunshine we will see.

Avalanche Summary

An early report on Monday of another skier remote triggered avalanche size 2.5 from 200 metres away on a southeast aspect at 2320 metres, believed to have released on the February 27th weak layer. A MIN report from Monday at Gorman lake in the Dogtooth range describes "a lot of cornice failures", as well as "many slides running full path." On Sunday, large cornice releases triggered persistent slabs on slopes below up to size 3.0 in the central part of the region, and a group of skiers remotely triggered a size 2.5 from 6 metres away on a southeast aspect at 2400 metres in the north of the region. On Saturday several natural and explosive initiated cornice failures to size 2.5 were reported. In the north of the region on friday control work produced several size 2 to 3 persistent slab avalanches on high elevation north through east facing features. These avalanches were failing on the mid and early February persistent weak layers.

Snowpack Summary

Recent moist surface snow has re-frozen into a crust at all elevations on solar aspects and up to at least 2000 metres on shaded aspects. Cornices continue to be described as large and fragile, and may fail with additional loading from forecast snow, or from high daytime temperatures. Some recent storm snow or wind slabs are likely to release as loose wet snow during periods of daytime warming. Buried persistent weak layers continue to be a concern for remote triggering in isolated areas where crusts are not strong enough to "bridge" the weakness. The late February surface hoar/crust weak layer is down 40-90 cm. This layer is still reactive to human triggers in some places while in other spots it's really tough to trigger, and there's not much of a reliable pattern telling us what exact aspects are most suspect. Deeper weak layers from mid-February and early January are now down 50-90cm and 70-120cm respectively. Triggering an avalanche on either of these layers has become unlikely but still has the potential to produce very large avalanches in isolated locations.

Regions covered