Bulletin d’avalanche

Kootenay Boundary

Dec 30 – 31, 2020Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Fri
Sat
Alpin
3 · Marqué
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Points saillants

With fresh snow on the way keep in mind we are concerned about buried weak layers. Cautious terrain selection remains important.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–1.5

    Watch for new snow and wind to form reactive slabs on leeward terrain in the alpine and near ridgetops.

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–2.5

    Weak layers of surface hoar and/or faceted grains overlie a hard melt-freeze crust 30 to 80 cm deep. The new snow load before Christmas pushed this problem over the tipping point and resulted in large avalanches. Although the likelihood of triggering persistent slab avalanches is decreasing, the potential for triggering a high consequence avalanche should still be top of mind in your decision making process. 

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

A weak frontal system crosses the region on Wednesday then a bigger system is poised to hit the region on the weekend.

TUESDAY NIGHT: Increasing cloud with snow starting around 3 am, moderate southwest wind, temperatures around -8 C.

WEDNESDAY: Flurries with 5-10 cm of snow, moderate southwest wind, temperatures around -6 C.

THIURSDAY: Flurries end early in the morning then mostly cloudy in the afternoon, moderate west wind, temperatures around -5 C.

FRIDAY: Flurries starting midday with a trace of new snow by the end of the day, moderate south wind, temperatures around -5 C.

Avalanche Summary

No new avalanches were reported on Monday, but a few skier triggered size 1 slab and loose avalanches were reported over the weekend. Many storm and persistent slab avalanches were observed last week. They were generally large (size 2), on west, north, and east aspects, 20 to 70 cm thick, and at elevations between 2000 and 2300 m. Although avalanche activity appears to have diminished, I wouldn't rule out the possibility of seeing more persistent slab avalanches.

Snowpack Summary

Stormy weather on Wednesday will bring 5-10 cm of new snow and could form new wind slabs in leeward terrain. Two weak layers are buried in close proximity to one another. They are 50-80 cm deep around Nelson and 30-50 cm deep around Rossland and other western parts of the region. The layers are composed of feathery surface hoar and sugary faceted grains and they overly a hard melt-freeze crust. There was substantial avalanche activity on these layers prior to Christmas from natural and human triggers. Although reports of such avalanches have been dwindling, these weak layers remain a concern, as they can produce large and destructive avalanches.

Terrain and Travel

  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Use conservative route selection and resist venturing out into complex terrain.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Régions couvertes