Bulletin d’avalanche

Northwest Coastal

Dec 24 – 25, 2020Avalanche Canada
Voir sur la carte
Archivé · expiré 6 years ago

Danger d’avalanche

Sat
Sun
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
Ouvrir la carte complète

Points saillants

Strong wind and a whole lot of snow = large avalanches! Staff safe friends, wait out the storm before you dive into avalanche terrain. 

Problèmes avalancheux

  • Persistent Slabs

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

    A weak layer of surface hoar is down 40-60 cm and seems to be very reactive to human triggers in the Nass Valley. At the moment the reports are localized. I'm uncertain where else it exists regionally. 

    A crust that was buried in early December is now down 80-120 cm and counting. Around this crust are facets and potentially surface hoar in sheltered areas. Human triggered avalanches and storm slabs may step down to this layer.

  • Storm Slabs

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

    Fresh storm slabs on Thursday will be very reactive and a widespread avalanche cycle is likely. Below treeline hazard is rated HIGH due to the potential of large avalanches from above running to that elevation.

  • Loose Wet

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

    Steep slopes and terrain features below treeline may see loose wet avalanche activity with the rising freezing levels and rain. 

Confidence

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

Weather Forecast

Yet another big storm batters the region through the forecast period. Hopefully, Santa will find his way through the wind and the snow!

Wednesday Night: Snow 20 cm. Alpine temperatures -3 and freezing levels 600 m. Ridgetop wind strong to extreme from the southwest. 

Thursday: Heavy snow 20-30 cm. Alpine temperatures -1 with freezing levels 1000 m. Ridgetop wind strong from the southwest.

Friday: Mix of sun and cloud. Alpine temperatures -4 and freezing levels 700 m. Ridgetop wind generally light with strong easterly gusts. 

Saturday: Cloudy with some flurries. Alpine temperatures near -3 and freezing levels 600 m. Ridgetop winds will be light.

Avalanche Summary

On Tuesday reports from the Beaupre sled area and the Nass Valley showed that storm slabs were easily triggered by humans up to size two. Check out the MIN posts here. Reports indicate that the storm slab may be sitting on a weak layer of surface hoar down 40-60 cm which is why the slab is so touchy. Explosive control also showed slabs up to size 2 and natural loose dry sluffing was seen from steeper terrain features. 

Thursday will be a different beast with the new storm. A widespread avalanche cycle is expected. 

Please consider sharing your observations with the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter!

Snowpack Summary

The incoming storm will build new and very reactive storm slabs, especially where the snow has been stiffened by the wind and/ or sit above a recent surface hoar layer buried 40-60 cm down. I'm uncertain how widespread this buried interface is throughout the region besides the Nass Valley. 

A crust that was buried in early December is now down 80-120 cm and counting in the alpine but is closer to the surface at and below treeline elevations. Around this crust are facets and potentially surface hoar in sheltered areas. Storm slabs may step down to this layer.

The early-November crust is buried around 100-200 cm at treeline. This crust may have weak and sugary facets above it in parts of the region. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

Régions couvertes