Avalanche forecast

Purcells

Mar 4 – 5, 2013Avalanche Canada
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Archived · expired 14 years ago

Avalanche danger

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

Avalanche problems

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–5
    Large looming cornices exist on ridgelines. These cornices may be weak and fail, especially if the sun shines through. The weight of cornice fall could trigger a slab avalanche on the slope below.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2–6
    Loading from new snow and wind may add reactivity to persistent buried surface hoar layers. In deeper snowfall areas, resulting avalanches may be large and destructive.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–5
    Recent new snow and wind have created new slabs. These may be particularly touchy on slopes lee of the wind and it may take several days for the storm snow to settle out. Skier and rider triggering is likely. Watch sluffing from steeper terrain.

Confidence

Good

Weather Forecast

Tonight and Tuesday: A weak ridge will remain over interior ranges with generally dry conditions. Ridgetop winds will blow moderate from the South. Light snow amounts. Alpine temperatures near -10 and freezing levels 1100 m.Tuesday night and Wednesday: A low pressure system will move inland. Most of this system will remain South of the border, but some cloud and light precipitation will spread into the Southern Interior ranges. Ridgetop winds light from the West. Alpine temperatures near -8 and freezing levels at 1400 m, falling to valley bottom overnight.Thursday: Generally clear and dry. Ridgetop winds light from the West. Alpine temperatures near -7 and freezing levels 1600 m the dropping overnight.

Avalanche Summary

Over the weekend the region saw a widespread large natural avalanche cycle, with avalanches up to size 3.5. On Sunday, numerous natural slab avalanches were reported up to size 2.5 on a a variety of aspects. Explosive avalanche control in region revealed several large slab avalanches up size 3.5.On Monday, explosive avalanche control produced a size 2.5 on a West aspect around 2900 m. No natural avalanche activity has been reported.

Snowpack Summary

Over the past week 60-80 cm snow fell. This new snow added to an ongoing storm snow instability, particularly on the west side of the region where accumulations have been highest. Buried surface hoar and sun crust layers exist up to 80cm below the surface and seem most prevalent on the west side of the region. Large avalanches initiated on these weak layers during the weekend storm. Large looming cornices exist on ridgelines and may become weak, especially when the sun comes out. Cornice fall could trigger slab avalanches on slopes below.A surface hoar layer buried on January 23 is still on the radar of some operators. This layer has been less likely to trigger by skiers, but may still be sensitive to large loads like avalanches in motion or cornice fall.Below treeline exists a melt-freeze crust which may be bridging instabilities deeper in the snowpack. If temperatures warm, you'll notice the crust breaking down and the snowpack becoming weaker.

Regions covered