Avalanche forecast

Purcells

Mar 19 – 20, 2021Avalanche Canada
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Archived · expired 6 years ago

Avalanche danger

Sun
Mon
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Fresh wind slabs may form throughout the weekend on upper elevation north, northeast & east facing slopes. Clearing Saturday afternoon could heat things up fast. Avoid being on or below cornices.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    Southwest winds and dribs and drabs of new snow may build thin wind slabs in lee terrain features. This problem may increase in sensitivity over the next few days as new snow and wind continue to build the slab. Steep, convex slopes below alpine ridge tops are the most likely places to trigger these slabs. 

    If the sun pokes out it may have enough punch to initiate the recent snow as loose wet or dry avalanches from steep terrain features. 

  • Cornices

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Where cornices exist they pose a threat both from the potential to collapse under your feet (or machine) and from the potential to send large chunks of snow far down a slope. If anything can trigger the more stubborn persistent weak layers it's a large falling cornice. They are most likely to fail during intense periods of solar radiation. Cornice failures are very unpredicatble. 

Terrain and Travel

  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • Avoid freshly wind loaded features, especially near ridge crests, roll-overs and in steep terrain.
  • Avoid exposure to slopes that have cornices overhead.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Looks like it’s back to winter for the next few days.

FRIDAY NIGHT: Freezing level lowering to about 800 m, light southwest wind with potential for moderate gusts, 1 to 3 cm of snow possible.

SATURDAY: Overcast, freezing level rising to about 1800 m, light to moderate southwest wind, 1 to 6 cm of snow expected in most locations. Convective flurries could produce 10+ cm in favoured locations.

SUNDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1500 m, light to moderate southwest wind, 1 to 4 cm of snow possible during the day with potential for another 1 to 5 cm Sunday night.

MONDAY: Broken cloud cover at dawn with skies steadily clearing throughout the day, freezing level beginning near valley bottom rising to about 1500 m, light northwest wind, 2 to 6 cm of snow possible.

Avalanche Summary

One small loose wet avalanches was reported on Wednesday and another on Thursday from solar aspects. A small wind slab was also reported from a high elevation east facing aspect Thursday.

On Tuesday, natural cornice falls were observed. Reports indicated that they did not pull a slab on the slope below. Sunshine may initiate loose wet avalanches on steep solar slopes and continue to weaken cornices.

Snowpack Summary

Surface hoar crystals can be found on Northerly aspects above 1800 m combined with dry wintery snow. On solar aspects and at lower elevations expect crusty snow in the morning and soft, moist snow in the afternoon. Large cornices may still pose a hazard close to alpine ridgelines, especially when it's warm and sunny.

A persistent weak layer of facets 40-60 cm deep that was buried in mid-February was reactive in the north of the region earlier this month but since the first week of March, only a couple of avalanches have been reported on this layer resulting from large triggers such as cornice fall. There are several other weak layers deeper in the snowpack composed of old surface hoar, facets and/or crusts, all of which have been recently unreactive.

Regions covered