Lawinenlagebericht

South Rockies

Feb 19 – 20, 2021Avalanche Canada
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Lawinengefahr

Sun
Mon
Hochgebirge
2 · Mässig
Waldgrenze
2 · Mässig
Unterhalb
1 · Gering
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Kernpunkte

Slabs on the late January persistent weak layer continue to be easily triggered by humans. For skiers and riders in the Elk Valley the Lizard-Flathead forecast with danger rating Considerable at treeline is more appropriate.

Lawinenprobleme

  • Wind Slabs

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

    Moderate westerly wind is forming fresh wind slabs on northeast to southeast facing lee terrain features in the alpine and open areas at treeline. Look out for wind slabs in unusual places. Recently localized moderate to strong winds blew from variable directions. 

    Wind slabs are slow to bond where they sit over cold sugary facets. There is also potential for wind slabs to step down to the late January persistent weak layer. 

    When the sun comes out wet loose avalanches might release on steep slopes which are directly hit by the sun.

  • Persistent Slabs

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

    This layer continues to be easily triggered by skiers and riders. 40-65 cm of snow sits above a buried weak layer of surface hoar, facets, and a crust (depending on elevation and aspect). Reports suggest the persistent weak layer at treeline in the Elk Valley is the biggest repeat offender, and things have been most reactive on northerly and easterly aspects, but don't let your guard down elsewhere. 

    Small terrain features are producing small avalanche results, bigger features can produce larger more dangerous avalanches. These kinds of avalanches can happen in surprisingly mellow terrain and be triggered from a distance away.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

THURSDAY NIGHT: Cloudy with clear periods, trace of new snow, moderate westerly wind, temperature low -13 C.

FRIDAY: Mostly cloudy with sunny periods, trace of new snow, moderate westerly wind, temperature high -7 C.

SATURDAY: Mix of sun and cloud, trace of new snow, moderate southwest wind, temperature high -5 C.

SUNDAY: Mostly cloudy, 3 cm new snow, moderate to strong southwest wind, temperature high -1 C, freezing level rising to 1700 m. 

Avalanche Summary

On Tuesday and Wednesday a few wind slab avalanches up to size 2 were triggered by explosives and released naturally. 

Several wind slab avalanches up to size 2 were triggered by skiers and released naturally at treeline and in the alpine on Monday. Human triggered avalanches were reported north of Crowsnest Pass. The avalanches were triggered on east aspects on mellow slopes in the alpine and at the treeline/alpine interface (see this MIN report). The failure plane of these avalanches is likely the late January persistent weak layer consisting of surface hoar, sugary facets or a crust/facet combination. 

Several skier triggered wind slab avalanches up to size 1.5 were reported on Sunday on usually and reverse loaded terrain features. 

Snowpack Summary

A few centimetres of new snow sit on top of wind affected snow surfaces, especially in the alpine and open areas at treeline, and a facet layer which is 20-30 cm thick in places. A persistent weak layer lurks 40-65 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack. Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be approached with caution.

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.

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