Avalanche forecast

Purcells

Mar 1, 2018Avalanche Canada
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Archived · expired 9 years ago

Avalanche danger

Fri
Sat
Alpine
3 · Considerable
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

Storm slabs on steep slopes, wind slabs on lee slopes, and a persistent slab that seems to be "waking up" on southerly slopes. There's lots to think about, and manage!

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2.5
    New snow and ongoing strong winds will continue to promote wind slab formation in wind-loaded areas on the leeward side of ridges and on cross-loaded slopes and gulleys. Storm slabs may also be found in sheltered area on steeper slopes and rolls.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–3
    An interface buried up to 70cm deep has "woken-up". This problem seems most reactive in south-facing terrain where buried crusts exist.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

An approaching Low and weak front should only bring light snow Wednesday afternoon and overnight with winds backing to the south.THURSDAY: light snow with moderate to strong southeast winds during the day. Treeline temperatures around -10 CFRIDAY: more snow overnight Thursday and possibly into Friday with up to 10 or even 15 cm possible. However, there's significant uncertainty about the just how much new snow will fall. Having said that, highest amounts will be in the south, less towards Golden. Light to moderate South winds.SATURDAY: trace to a few centimetres of snow, light and variable winds, continued treeline temperatures of around -10 C.

Avalanche Summary

Recent avalanche activity has consisted of mainly wind slabs (skier triggered and skier remote) in the size 1-1.5 range. However, we've also received reports of persistent slab avalanches (to size 3) where recent accumulations have been the highest. These avalanches, were skier-triggered or remotely triggered (from a distance) on Monday and naturally occurring on Tuesday with wind loading on cross-loaded slopes. We suspect the buried sun crust buried mid-February.Deep persistent avalanche activity has become less frequent over the past week.

Snowpack Summary

Around 30 cm of recent storm snow is being redistributed into deeper, reactive slabs in wind-exposed terrain. Up to 60cm below the surface there's a layer buried mid-February that's a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above.There are several deeper layers that have shown signs of improving but still remain suspect as low probability - high consequence avalanche problems. I'm talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall, smaller avalanches coming down from above); human triggering is also possible in shallow snowpack areas with convoluted terrain.

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