Boletín de aludes

Purcells

Mar 24 – 26, 2020Avalanche Canada
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Archivado · caducó 7 years ago

Peligro de aludes

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

Small wind slabs below ridgetops are currently the primary concern. 

Problemas de aludes

  • Wind Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1–1.5

    Recent winds may have formed reactive slabs on lee features below ridgetops.

  • Deep Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Unlikely - Possible
    Tamaño
    2–3.5

    Weak faceted snow near the base of the snowpack continues to be a concern. Treat wind-scoured, rocky, shallow terrain as suspect and avoid big alpine slopes that are threatened by cornices overhead. 

Confidence

Low - Uncertainty is due to the limited number of field observations.

Weather Forecast

TUESDAY NIGHT: Partly cloudy, light southwest winds, alpine low -10 C, freezing level valley bottom.

WEDNESDAY: Mix of sun and cloud, light west winds, alpine high -4 C, freezing level 1200 m.

THURSDAY: Mix of sun and cloud, moderate west winds, alpine high -2 C, freezing level 1400 m.

FRIDAY: Cloudy with possible flurries; 0-3 cm, moderate west winds, alpine high -1 C, freezing level 1600 m

Avalanche Summary

Over the past week, avalanche activity was reported as natural loose wet avalanches (size 1-2.5) running in steep, sun-exposed terrain. One large (size 2.5) cornice failed as a result of explosive mitigation.

Last week there was a report of a skier remotely triggering (from a distance) a large (size 2) deep persistent slab avalanche at 2600 m on a northwest aspect. The avalanche was triggered from a thin spot, released 40-80 cm deep, and ran on depth hoar near the base of the snowpack.

Snowpack Summary

Sunday's storm only produced a few cm of snow with light to moderate wind mainly out of the southwest. 

The new snow is falling on a variety of snow surfaces, consisting of sun crusts, hard wind-affected snow, and soft faceted snow. There have also been reports of surface hoar forming on sheltered, shady slopes. See this MIN for a helpful illustration from nearby Glacier National Park. It will be important to track the depth, cohesiveness, and bond of the new snow to these various old snow surfaces across aspects and elevations where you are travelling.

Cornices are large and looming. Surface hoar buried February 22 may be found 50-100 cm deep. Avalanche activity on this layer was last reported March 11th. 

Deeply buried facets lurk near the bottom of the snowpack. This layer has been responsible for sporadic deep persistent slab avalanches, usually triggered from shallow, rocky start zones.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
  • Make observations and assess conditions continually as you travel.
  • Be alert to conditions that change with aspect and elevation.

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