Boletín de aludes

Lizard-Flathead

Jan 31 – Feb 1, 2021Avalanche Canada
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Archivado · caducó 6 years ago

Peligro de aludes

Tue
Wed
Alta montaña
3 · Notable
Límite del bosque
3 · Notable
Bajo el límite
2 · Moderado
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Lo esencial

Storm slabs are reactive to human triggers at all elevations and particularly where the new snow overlies surface hoar. Moderate to strong southwest wind will form fresh wind slabs at higher elevations. 

Problemas de aludes

  • Storm Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Likely
    Tamaño
    1–2.5

    20-30 cm of recent storm snow has formed reactive storm slabs in the alpine and at treeline elevations. With rising temperatures throughout the day the new snow slab might become stiffer and a failure in the weak layer underneath might propagate wider than expected resulting in larger avalanches. The storm slabs are particularly reactive where they overlie surface hoar in sheltered areas at and below treeline.

    The new snow is redistributed by moderate to strong southwest wind and forms fresh wind slabs on lee terrain features at higher elevations. 

    Cornices might grow larger and become more fragile.

Confidence

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

Weather Forecast

SATURDAY NIGHT: Mostly cloudy with clear periods, 3 cm new snow, moderate to strong southwest wind, treeline temperature -6 C, freezing level at 900 m.

SUNDAY: Mix of sun and clouds, up to 4 cm new snow, moderate to strong southwest wind, treeline temperature -4 C, freezing level at 1400 m.

MONDAY: Cloudy, 10-15 cm new snow, moderate southwest wind, treeline temperature -2 C, freezing level at 1700 m.

TUESDAY: Cloudy, 20-25 cm new snow, moderate southwest wind, treeline temperature -3 C, freezing level at 1500 m.

Avalanche Summary

Several skier and explosives triggered slab avalanches up to size 2 were reported on Saturday as well as a few natural cornice failures. A few small natural slab avalanches were observed on Saturday (see this MIN report). Several slab avalanches up to size 2 released naturally and were triggered by explosives and skiers on Thursday and Friday. Some avalanches were larger than expected (see this valuable MIN post). Other parties reported signs of instability as whumpfing and shooting cracks. Loose dry avalanches (sluffs) in steep alpine and treeline features were observed in the last few days. 

Snowpack Summary

20-30 cm recent snow buried surface hoar and other old surfaces. In the alpine, the new snow sits on top of layers of hard wind slab, scoured areas, sastrugi and isolated pockets of soft snow. A hard crust underneath the new snow is found up to 1800 m.    

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

  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.
  • 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.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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