Lawinenlagebericht

Purcells

Dec 29 – 30, 2020Avalanche Canada
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Lawinengefahr

Thu
Fri
Hochgebirge
3 · Erheblich
Waldgrenze
3 · Erheblich
Unterhalb
2 · Mässig
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Kernpunkte

  

Multiple critical weak layers in the snowpack that could produce large avalanches remain possible to human trigger and are keeping the hazard elevated. A disciplined approach to decision making is needed to play safe.

Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    1–2

    Lingering wind slabs may remain reactive to human triggers on a variety of aspects.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible - Likely
    Größe
    2–3

    A weak layer of surface hoar down 50-100 cm. has been reactive to human triggers, resulting in large avalanches.

  • Deep Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible
    Größe
    2.5–4

    A Crust buried near the bottom of the snowpack has been responsible for some very large explosive triggered avalanches up to size 4.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

  

MONDAY NIGHT: Partly cloudy / Light, northwest ridgetop wind / alpine low temperature -15 / Freezing level valley bottom.

TUESDAY: Mix of sun and cloud / Light, northwest ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.

WEDNESDAY: Cloudy / Moderate, southwest ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

THURSDAY: Cloudy with flurries; 0-3 cm. / Light, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.

Avalanche Summary

On Sunday, a size 2.5 explosive triggered persistent slab avalanche was reported on a north aspect near Golden. Another reminder that on the wrong piece of terrain, very large avalanches are still possible to trigger.

On Saturday, a skier remotely triggered an avalanche on a southwest aspect below treeline, north of Kicking Horse Mountain Resort. No size was reported.

Snowpack Summary

Winds blowing from a variety of directions last week formed wind slabs in lee features at treeline and above.

There are currently several critical layers of concern. The early December surface hoar is down 30 to 80 cm. It has recently been sensitive to remote triggering which is well illustrated in this MIN post from the Golden area.

Below, or near the surface hoar you may encounter a crust. This crust has been observed as high as 2400 m. in the south of the region and 1800 m. in the north.  

The lower snowpack is characterized by more crusts, the most notable is a rain crust from early November that is 50 to 130 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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