Lawinenlagebericht

Purcells

Dec 7 – 8, 2011Avalanche Canada
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Archiviert · abgelaufen 15 years ago

Lawinengefahr

Fri
Sat
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Lawinenprobleme

  • Wind Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Possible - Likely
    Größe
    1–3
    Stiff wind slabs in the alpine and open areas at treeline may be triggered by skiers and riders. It may be possible to remotely trigger a slide from a weak spot nearby.

  • Persistent Slabs

    • Hochgebirge
    • Waldgrenze
    • Unterhalb der Waldgrenze
    Wahrscheinlichkeit
    Unlikely - Possible
    Größe
    2–5
    The weak facetted layer near the ground may still be triggered by human activity. Areas with a lot of variability in the snow cover may be the most suspect. Triggering may occur from weak spots like rocks or clumps of small trees.

Confidence

Fair - Freezing levels are uncertain on Friday

Weather Forecast

Thursday, Friday, and Saturday are forecast to be mostly clear and sunny with freezing down to the valley at night and rising slightly above the valley during the warmest part of the day. The freezing level on Friday may rise up to about 1200 metres. These conditions are prime for surface hoar to develop and continue to grow. We may continue to develop sun crust on steep slopes in the alpine that are exposed to the sunshine. Winds should be light from the west, but we may see some moderate outflow winds from the north in the alpine.

Avalanche Summary

No new avalanche observations from this region. We have dropped the danger rating in the alpine to moderate. It is still likely that you could trigger a windslab in steep terrain. Triggering a full depth release is getting less likely, but weak spots are sure to exist that may propagate a large avalanche. The snow pack is still relatively young and needs some time to mature. I am having a hard time dropping the treeline danger level to LOW because I think the snowpack is weaker and more variable in this region than it is to the west.

Snowpack Summary

I wrote this on Monday, but I am going to leave it in here again today. There is not much change taking place. Previous problems are healing slowly, and I don't think it is cold enough to cause much facet growth in the base layers. We suspect that surface hoar may be growing during the clear cold weather that has dominated over the past few days. Some steep south facing slopes may have developed a thin sun-crust. Windslabs continue to be a concern in the Purcells. Strong winds last week developed unstable slabs of transported snow on steep terrain in the alpine and at treeline. Snow depths are quite variable through the region. In the alpine there is 170- 250cm. At treeline there is anywhere from 130-150cm.The upper snowpack is tightening up forming a stronger mid-pack. A highlighted concern for the Purcells was the mid-November storms that created a heavy slab over a weak basal faceted base, resulting in a significant cycle of large avalanches running full depth.

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