Bulletin d’avalanche

Lizard-Flathead

Feb 17 – 18, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Fri
Sat
Alpin
2 · Modéré
Limite forestière
3 · Marqué
Sous la limite
1 · Faible
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Points saillants

Conservative decision-making is still essential! Slabs on the late January persistent weak layer consisting of surface hoar and sugary facets continue to be reactive to skiers and riders. Don't let your guard down while this layer takes its time to heal.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1–2

    Look out for wind slabs in unusual places. There have been some localized moderate to strong winds from variable directions during the weekend. 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 reports suggested avalanches failing up to 70 cm deep. These avalanches can be triggered from a distance away.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2.5

    Human triggering of this layer is likely. Small terrain features are producing small avalanche results, bigger features produce larger more dangerous avalanches. 40-65 cm of snow sits above a buried weak layer consisting of surface hoar, facets, and a crust (depending on elevation and aspect). The surface hoar interface is the biggest repeat offender, and things have been most reactive on northerly and easterly aspects at treeline and the treeline/alpine interface, but don't let your guard down elsewhere! These kinds of avalanches can happen in surprisingly mellow terrain and can 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: Mostly cloudy, trace to 5 cm new snow, light westerly wind, temperature low -15 C.

WEDNESDAY: Mix of sun and cloud, trace of new snow, light northwest wind, temperature high -7 C.

THURSDAY: Mix of sun and cloud, trace of new snow, light westerly wind, temperature high -8 C.

FRIDAY: Mostly cloudy, up to 5 cm new snow, light southwest wind, temperature high -7 C.

Avalanche Summary

On Monday, skiers triggered size 1 avalanches at treeline and in the alpine on northeast aspects. One avalanche was triggered from a short distance away (see this MIN report). On Sunday skiers triggered avalanches up to size 2.5 on open features at the treeline/alpine interface in the Lizard Range and Tunnel Creek. These failed on the late January persistent surface hoar layer (see this MIN as an example). 

On Thursday and Friday there were human and remote triggered avalanches up to size 2 reported. Locations like Mount Fernie, 2000, Liverwurst and McDermid were a few location examples. Some avalanches were triggered from a distance away. 

Snowpack Summary

Surface faceting and surface hoar growth is promoted by clear nights and frigid temperatures. Below 1600 m a hard melt-freeze crust is underneath 20-40 cm recent snow. 

A persistent weak layer lurks 30-70 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. This weak interface has been responsible for the majority of recent avalanches. Reports suggest the surface hoar interface at treeline 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 a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which is currently unreactive. 

Terrain and Travel

  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.

Régions couvertes