Bulletin d’avalanche

Purcells

Dec 22 – 23, 2021Avalanche Canada
Voir sur la carte
Archivé · expiré 5 years ago

Danger d’avalanche

Fri
Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
Ouvrir la carte complète

Points saillants

Another winter storm will likely build fresh and reactive storm slabs by Wednesday afternoon and into Thursday, especially on leeward slopes that are wind-loaded.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    1.5–3.5

    A layer of weak facets (sugary snow) can be found down 50-100 cm over a crust that formed in early December. This layer is starting to produce avalanches across the province and as we assess the additional load on this layer from the storm, it will be critical to employ good travel habits and diligent decision making.

    At the base of the snowpack above 2200 m, a layer of depth hoar lingers. Avalanches-in-motion have the potential to step down to this layer. 

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–2

    Reactive storm slabs will build through the day with new storm snow and strong southwest wind, especially in the southern part of the region that receives higher snowfall amounts. 

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system.

Weather Forecast

Expect some enhanced snowfall amounts in the southern part of the region Wednesday through Thursday as a warm and wet air mass rises from the South and collides with the predominant colder air mass sliding down from the North.

Tuesday Night: Trace of new snow with strong ridgetop wind from the SW. Alpine temperatures near -13 and freezing levels at the valley bottom.

Wednesday: New snow throughout the day, heavy at times with 10-15 cm accumulation. Strong to extreme ridgetop wind and alpine temperatures near -5. Freezing levels 1000 m.

Thursday: Heavy snowfall amounts, 10-20 cm accompanied by strong SW winds. Alpine temperatures near -5 and freezing levels rising to 1100 m.

Friday: Mostly cloudy with some flurries. Gusty ridgetop winds from the South and freezing levels dropping back to the valley bottom. 

Avalanche Summary

No updated reports by Tuesday afternoon. 

On Sunday, operators reported ski cutting and explosive storm slab results to size 1 in the alpine and treeline.

New snow and wind will likely build reactive storm slabs. Loose-dry sluffing may be seen from steep terrain features.

Snowpack Summary

New snow and wind will likely build reactive storm slabs through Friday and older wind slabs at upper elevations below ridgecrest may continue to be reactive to human triggers. Low-density storm snow exists in sheltered terrain. 

Below this new snow, 40-60cm of consolidated snow sits over a substantial crust that formed in early December. This crust is 10-30 cm thick and can be found down 60-120 cm. It is present across aspects below 2300m. A thin layer of weak facets (sugary snow) can be found above this crust that has demonstrated reactivity in snowpack tests. This problem is particularly hard to predict and tricky to manage. For this reason wide, conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog. 

A late October facet/crust layer of concern sits at the bottom of the snowpack above 1900m. Although this layer has been trending less reactive, it remains on our radar.

The snowpack depth at treeline is around 115-200 cm. The deepest snowpack can be found near the Bugaboos. 

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Be careful as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Régions couvertes