Bulletin d’avalanche

Purcells

Dec 11 – 12, 2021Avalanche Canada
Voir sur la carte
Archivé · expiré 5 years ago

Danger d’avalanche

Mon
Tue
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
Ouvrir la carte complète

Points saillants

Today is a good day to choose mellow slopes that are protected from the wind. Time will tell how well the new snow bonds to the wind slabs and crust that it covered. 

Problèmes avalancheux

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–2.5

    Underneath the new storm snow, there are lingering wind slabs on most aspects, due to recent, strong winds of varying direction. An avalanche that starts in the storm snow has the potential to step down to these wind slabs, that were most prominent at treeline and in the alpine.

    If you are unsure where the old wind slabs are lurking, then assume any storm slab avalanche has the potential to get bigger than expected.

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3.5

    A widespread weak layer of facets and depth hoar exists at the base of the snowpack above 1900m.

    Avoid thin and rocky start zones where this layer may sit closer to the surface, and big open slopes capable of producing large avalanches.  

Confidence

Moderate - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

FRIDAY NIGHT: Mostly cloudy. 5-10 cm of snow expected. Strong southwest wind. Alpine low around -13.

SATURDAY: Overcast. 10-20 cm of snow expected. Possibly another 10 cm overnight. Strong to extreme southwest winds. Expect wind speed to increase drastically as you gain elevation. Freezing levels climb to between 1000 and 1500m. Alpine highs of -3. 

SUNDAY: Mostly cloudy. 0-7 cm snow expected. Moderate to strong southwest wind. Freezing levels below 1000m. Alpine highs of -6. 

MONDAY: Mostly cloudy. 0-5 cm snow expected. Light to moderate south winds. Warming through the day, alpine high around -7.

Avalanche Summary

No new avalanches observed. Expect human triggered avalanches to become likely as the storm snow accumulates.

On Wednesday, natural and skier triggered slab avalanches were observed at treeline and above to size 1.5.

Explosive control work near Golden on Dec 5th produced a size 2 slab avalanche that failed to ground in a steep and unsupported terrain feature. A naturally triggered size 3 was also observed on a west facing slope in the Northern zone of the Purcells, believed to have occurred around the 2nd of December. 

Two Mountain Information Network (MIN) reports (MIN 1 and MIN 2) from Dec 3 in Quartz Creek also reported deep persistent avalanches failing at the base of the snowpack. 

While these observations are almost a week old, this deeply buried weak layer is still a concern.

Snowpack Summary

Over the course of the day, 15-25 cm of new snow that is falling with strong wind and warming temperatures has the potential to create a reactive, upside-down snowpack. 

The new storm snow is falling on 50cm of settling snow from the last storm. This overlies a thick and supportive melt freeze crust on all aspects up to 2400m. Westerly winds have redistributed new snow into deeper deposits in wind loaded features at higher elevations.

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. This layer has been reactive to human triggers, producing large avalanches. This layer is widespread and will likely continue to be a layer of concern.

Average snowpack depth at treeline is 100-180cm, with the deepest snowpack found near the Bugaboos. 

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Be aware of highly variable recent wind loading patterns.
  • Be mindful that deep instabilities are still present and have produced recent large avalanches.

Régions couvertes