Boletín de aludes

Lizard-Flathead

Feb 3 – 4, 2021Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Fri
Sat
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Lo esencial

New snow accompanied by a strong southwest wind will build touchy and reactive slab avalanches, especially where they sit above a surface hoar, facet or crust interface. Natural avalanche activity may taper but skier and rider triggers are likely.

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    A cohesive slab 30-45 cm thick now sits above a buried weak layer of surface hoar and surface facets. These slabs have been very reactive to human triggers showing wide propagations in moderate to low angle terrain. They have been catching people by surprise, so pay attention to signs of instability and stay clear of terrain traps like creeks, cliffs, and depressions below you.

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1.5–2.5

    Strong southwest wind and new snow will build reactive storm slabs at all elevations. Cornices are large and fragile and don't respond well to rapid change- like new load from snow or rain, rapid warming or rapid cooling. They deserve respect and a wide berth from above and below. 

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: Snow amounts 5-15 cm. Ridgetop wind generally light from the southwest with strong gusty periods. Alpine temperatures near -7 and freezing levels at valley bottom.

Wednesday: Mix of sun and cloud. Ridgetop wind moderate from the West. Alpine temperatures near -5 and freezing levels 1100 m.

Thursday: Cloudy with flurries. Ridgetop wind light to moderate from the southwest. Alpine temperatures near -10 and freezing levels at valley bottom.

Friday: Light snow up to 5 cm. Ridgetop wind generally light with some strong gusts from the West and freezing levels at valley bottom.

Avalanche Summary

On Tuesday, a widespread natural avalanche cycle occurred up to size 2.5. 

On Monday, several storm slab and loose dry avalanches up to size 2 were triggered with the use of explosives. Reports of natural cornice failures were seen up to size 2. On Sunday, numerous storm slab and persistent slab avalanches were reported up to size 1.5 primarily on NE aspects above 1700 m. These avalanches were easily triggered by the weight of a human either directly or remotely (from a distance away). Check out these reports that show how reactive the slab is: MIN Report, MIN report, or this MIN report. 

With additional forecast snow and strong wind, skier and rider triggered avalanches will be likely on Wednesday. 

Snowpack Summary

Up to 45 cm of recent snow has formed a cohesive and reactive slab that sits above a weak interface of surface hoar and surface facets (weak sugar or feather-like snow crystals). In the alpine, this slab of recent snow sits on top of a plethora of old snow surfaces comprising of hard wind slab, scoured areas, sastrugi, and isolated pockets of soft snow. Below 1800 m a hard melt-freeze crust underneath the new snow is found. Moist surface snow now exists below 1600 m. Once the freezing levels drop Tuesday evening the surface snow at lower elevations will likely form a crust.

A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which are currently unreactive. 

Terrain and Travel

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Persistent slabs have potential to pull back to lower angle terrain.
  • Avoid terrain traps where the consequence of any avalanche could be serious.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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