Avalanche forecast

Purcells

Jan 27 – 28, 2019Avalanche Canada
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Avalanche danger

Tue
Wed
Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
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Highlights

The snowpack in the Purcells this season is exceptional, and not in a good way. We've summarized our thoughts on this precarious snowpack in the latest forecasters blog here. Take it easy out there, this is not the time for the big lines.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1.5–2.5
    Wind over the last 48 hours has been out of the south, southwest, west and northwest with more than enough oomph to form wind slabs. These wind slabs may rest on a crust, or perhaps even buried surface hoar near treeline.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible - Likely
    Size
    1–2
    10 to 50 cm of snow sits above a weak interface of surface hoar and crust. The recent warm to cold temperature transition has allowed a more cohesive slab to form above the surface hoar which is most prevalent between at and below treeline.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    2.5–4
    The last avalanche observed on the weak facet/crust interface at the ground was Thursday, but human triggered avalanches remain possible. Is it a 1 in 100 slope, or a 1 in 1000 slope problem now? We're not sure and this is what makes it so tricky.

Confidence

High -

Weather Forecast

High pressure, cold temperatures and clear skies should allow for great visibility Monday and Tuesday. Cloud cover starts to build back in Wednesday, but the models are not showing any significant precipitation until Friday.SUNDAY NIGHT: Freezing level at valley bottom, light to moderate north/northwest wind, trace of precipitation possible.MONDAY: Clear skies at dawn, with a few clouds building in the afternoon, freezing level at valley bottom, light northerly wind, no precipitation expected.TUESDAY: Clear skies, freezing level at valley bottom, light west/northwest wind, no precipitation expected.WEDNESDAY: Scattered cloud cover, freezing level at valley bottom, light northwest wind, trace of precipitation possible.

Avalanche Summary

On Friday and Saturday wind slab avalanches up to size 2 were reported from east and northeast aspects between 1900 and 2400 m. One skier-triggered avalanche was reported on Wednesday in storm snow at approximately 2000 m that released 40 cm below the surface. On Thursday, explosive control work released another slide on the deep persistent layer at the base of the snowpack. There is a great MIN report from last Saturday that shows a natural avalanche (size 3.5) in International Basin, also on the deep persistent layer. Check out the MIN here.

Snowpack Summary

Saturday delivered warmth and strong to extreme wind out of the south, southwest and northwest. This left a crust on steep south facing aspects and likely redistributed quite a bit of snow into fresh and potentially deep wind slabs in lee alpine features. The warmth also allowed 10 to 50 cm of snow to continue to consolidate above the mid-January persistent weak layer (PWL). This PWL is made up of large surface hoar that is most prevalent at and below treeline. On steep solar aspects this interface presents as a crust, there may be locations where the surface hoar actually sits on the crust.The snowpack is also harboring a nasty weak layer near the ground that is made up of weak faceted grains above a crust. This interface continues to produce sporadic avalanches that are very large and destructive. Avalanches triggered on this weak layer take the entire seasons snowpack with it and have resulted in numerous close calls and serious incidents. This layer is most likely to be triggered from zones where the snowpack is thin and weak. Rock outcroppings and ridge crests around large open slopes and bowls in the alpine are particularly suspect

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