Boletín de aludes

Purcells

Feb 15 – 16, 2022Avalanche Canada
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Archivado · caducó 5 years ago

Peligro de aludes

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

Don't rely on surface conditions for clues to where the tricky persistent problem still exists. Open slopes at treeline are the most concerning, where buried surface hoar may be preserved. 

Whumpfing, shooting cracks and recent avalanches are clear signs of an unstable snowpack. 

Problemas de aludes

  • Persistent Slabs

    • Alta montaña
    • Límite del bosque
    • Bajo el límite del bosque
    Probabilidad
    Possible
    Tamaño
    1.5–2.5
    • A layer of surface hoar from late January is buried 20-50 cm deep. On solar aspects and at lower elevations surface hoar sits over a melt freeze crust. 
    • Another layer of surface hoar/facets over a crust from early January is buried 60-100 cm deep. 

    Treat sheltered open slopes at a treeline with extra caution where the surface hoar is most likely to be preserved - like cut blocks. Deeper instabilities could be triggered in shallow snow pack areas or by a large load such as a cornice or step down avalanche. 

    Avalanche activity is less likely where a thick and supportive crust sits on the surface. 

Snowpack Summary

Exposed terrain at alpine and treeline elevations hold dense wind effected surfaces with large cornices from westerly winds. Sheltered areas and lower elevations hold a widespread melt freeze crust.

The late January interface is buried 20-50cm deep, and consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine. Surface hoar sits above the crust in sheltered areas at treeline and below.

Several surface hoar layers are now buried in the upper snowpack 40-120cm deep. The snowpack below is well consolidated, with the early-December crust/facet persistent weak layer buried 80-150 cm deep. It is currently considered dormant. We expect this layer to become active later this season, check out the forecaster blog for more information.

Confidence

High - We have a good understanding of the snowpack structure and confidence in the weather forecast Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

The cold front moves out of the region tonight, light flurries continue Tuesday. A high pressure system builds Wednesday, bringing mostly dry conditions and scattered cloud.

MONDAY NIGHT: Cloudy with flurries, trace to 3 cm overnight. Freezing levels around 500 m in the north with an inversion possible, 1000 m in the south. Light northwest winds and an alpine high of -4. 

TUESDAY: A mix of sun and cloud. Chance of flurries. Moderate northwest winds with an alpine high of -2. Freezing levels rise to 1300m in the afternoon. 

WEDNESDAY: A mix of sun and cloud. Chance of flurries. Moderate northwest winds, alpine high of -3 with 1300m freezing levels. 

THURSDAY: Increasing cloud. Chance of flurries. Strong northwest winds. Freezing levels rise toward 2000 m. Alpine high of 0. 

Avalanche Summary

Last weeks warming trend and sun produced naturally and human triggered loose wet avalanches to size 2.5, mainly in steep sun baked terrain features. Natural cornice failures were observed, triggering small wind slabs on the slope below. 

As expected, persistent slab activity also increased during the warmer weather. Explosive control work on Sunday triggered a small avalanche that stepped down to the January surface hoar layer, producing a size 2.5 avalanche. On Saturday several natural persistent slabs were triggered by tree bombs and cornice failures. These failed on the late January surface hoar layer, on all aspects at treeline. 

Terrain and Travel

  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Be alert to conditions that change with aspect and elevation.
  • Be careful as you transition into wind affected terrain.

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