Boletín de aludes

South Rockies

Feb 17 – 18, 2021Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Fri
Sat
Alta montaña
2 · Moderado
Límite del bosque
2 · Moderado
Bajo el límite
1 · Débil
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Lo esencial

Slabs on the late January persistent weak layer consisting of surface hoar and sugary facets are still reactive and can be triggered in mellow terrain and from a distance away. Don't let your guard down! Read our latest forecaster blog on "Managing Moderate".

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–2

    Look out for wind slabs in unusual places. There have been some localized moderate to strong winds from variable directions. These winds have redistributed loose snow developing wind slabs in lee features, especially in the alpine and open areas at treeline. Newer reactive wind slabs will be 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. In some locations wind slabs sit directly on the persistent weak layer. Recent avalanches were triggered by humans on mellow slopes and 60 cm deep.  

    In sheltered zones the surface snow is becoming faceted and sugary and sluffing should be expected in steep terrain.

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible - Likely
    Tamaño
    1–2

    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 and the treeline/alpine interface in the Elk Valley and north of Crowsnest Pass close to the BC boarder are the biggest repeat offenders, 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

TUESDAY NIGHT: Clear with cloudy periods, trace of new snow, light to moderate northwest wind, temperature low -15 C.

WEDNESDAY: Mix of sun and cloud, trace of new snow, light northwest wind, temperature high -9 C.

THURSDAY: Sunny with cloudy periods, light westerly wind, temperature high -8 C.

FRIDAY: Mostly cloudy, trace of new snow, moderate southwest wind, temperature high -6 C.

Avalanche Summary

Several wind slab avalanches up to size 2 were triggered by skiers and released naturally at treeline and in the alpine on Monday. A couple human triggered avalanches were reported north of Crowsnest Pass. The avalanches were triggered on east aspects on gentle 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. Older natural avalanche activity of up to size 3 was reported as well on Sunday dating back a couple days. Reports on whumpfing and cracking of the upper snowpack were varied. Some parties experienced whumpfs and cracks (see this MIN report) whereas others didn't (see this MIN report).

A skier accidentally triggered a size 1.5 wind slab in a reverse loaded feature on the Alberta side of the region on Saturday.

Snowpack Summary

The snow surface is wind affected, especially in the alpine and open areas at treeline. Cold temperatures promote faceting of the snow surface. 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. Reports suggest the surface hoar interface 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. 

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.
  • If triggered, loose dry avalanches may step down to deeper layers resulting in large avalanches.

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