Bollettino valanghe

Northwest Coastal

Mar 9 – 10, 2022Avalanche Canada
Vedi sulla mappa
Archiviato · scaduto 5 years ago

Pericolo valanghe

Fri
Sat
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
Apri la mappa completa

In sintesi

Another sunny day! Wind slabs will form with moderate to strong wind from the northeast. Two buried persistent weak layers that consist of feathery surface hoar and a crust with sugary facets are still of concern.

Problemi valanghivi

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible - Likely
    Dimensione
    1–2

    The wind is forecast to blow moderate to strong from the northeast overnight Tuesday to Wednesday. Fresh wind slabs will build behind ridge crests and in lee terrain features in the alpine and at exposed treeline.

    On Sunday, strong to extreme wind from the northwest formed wind slabs. These slabs might still be reactive to human triggers, especially where they sit on feathery surface hoar. 

    Triggered wind slabs might step down to deeper buried weak layers and result in larger avalanches. 

  • Cornices

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely - Possible
    Dimensione
    1–2

    Cornices are large and can become weak with sun exposure. Caution around slopes that have cornice hazard above. Keep in mind that firm cornices can pull back into flat terrain at ridgetop if they fail. 

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Unlikely - Possible
    Dimensione
    1.5–2.5

    A layer with weak, feathery surface hoar crystals is buried 25-50 cm deep at sheltered treeline features and in the lower alpine.

    A thick crust is buried 60-100 cm deep. Avalanches on this layer will likely reach large sizes.

    A few, skier triggered avalanches and isolated natural activity up to size 2 were reported on both layers in the last few days.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

Tuesday night: Clear, moderate to strong northeast wind, alpine low -8 °C, freezing level at valley bottom.

Wednesday: Sunny, moderate northeast wind switching to moderate west wind around noon, alpine high -6 °C, freezing level at 500 m.

Thursday: Cloudy, 5-10 cm new snow, moderate to strong southwest wind, alpine high -5 °C, freezing level at 500 m.

Friday: Cloudy, 20 cm new snow, extreme southwest wind, alpine high -2 °C, freezing level at 1000 m.

Avalanche Summary

There have been a few, skier triggered slab avalanches to size 2 on the two buried persistent weak layers described in the Snowpack Summary in the last few days.

A skier triggered a small wind slab from a distance away on a northeast facing alpine slope on Monday. The avalanche released on feathery surface hoar that was buried in late February. Several natural wind slab avalanches and cornice failures up to size 2 were observed in the alpine. 

On Sunday, a large (size 3) wind slab released naturally in steep alpine terrain and many small natural wind slab avalanches up to size 1.5 were reported. One was triggered by a failed cornice. Skiers triggered small (size 1) wind slabs on south, east and north facing slopes in the alpine. Loose wet avalanche activity to size 1.5 was observed on steep sun-exposed slopes.

Snowpack Summary

There's a lot going on in the upper snowpack. Careful assessment is recommended. 

The snow surface is heavily wind affected in wind exposed areas. There is a crust on the surface below around 1000 m and on solar aspects below around 1200 m.

Feathery, weak surface hoar crystals buried around February 26th are found down 25-50 cm, most prominently at treeline elevations. This layer has been reactive to skier traffic in the last few days. 

A thick crust buried in mid-February is now found down 60-100 cm. Skiers triggered avalanches on this layer last weekend.  

The lower snowpack is effectively bridged by the layers above, and we do not expect avalanches to be triggered in the lower snowpack at this time. 

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Minimize your exposure time below cornices.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Be aware of the potential for large avalanches due to the presence of a buried crust.

Regioni coperte