Bulletin d’avalanche

North Rockies

Feb 23 – 25, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Thu
Fri
Alpin
4 · Fort
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

There was a report of an avalanche fatality in the Hasler area on Saturday. Heavy snowfall over the weekend has increased the likelihood and consequence of triggering a persistent slab avalanche. Adopt a conservative approach to terrain selection in the coming days.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    1.5–3

    Heavy snowfall and an overall warming trend has likely made a weak layer of surface hoarthat developed late-January reactive to riders. The layer can be found 50 to 110 cm deep across the region, being deepest in the south and shallowest in the north. This layer has been the most sensitive right at treeline, but it may extend up into the alpine, and be found in openings in the trees below treeline. 

  • Storm Slabs

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

    New reactive wind and storm slabs have formed with the 30-70+ new snow falling and strong winds blowing through the weekend. The snowpack will take time to adjust to the new load.

Confidence

Moderate - Uncertainty is due to limitations in the field data.

Weather Forecast

MONDAY Night: Cloudy with isolated flurries, light to moderate west wind, alpine temperature -5 C, freezing level 1000 m.

TUESDAY: Mix of sun and cloud, moderate to strong west wind, alpine temperature -7 C.

WEDNESDAY: Cloudy with sunny breaks and isolated flurries, moderate to strong southwest wind, alpine temperature -8 C.

THURSDAY: Snow, accumulation 10-15 cm, moderate west wind, alpine temperature -5.

Avalanche Summary

There is a preliminary report of an avalanche fatality in the Hasler area on Saturday. The details are still limited at this time, but the incident happened on a northeast aspect between 1400 and 1500m. The avalanche was a size 2. The fracture line was estimated to be 50-100 cm and is suspected to have been a persistent slab avalanche running on a weak layer of surface hoar. Click here to link to a report on the incident.

There was likely a widespread natural avalanche cycle on Sunday and Monday as a result of heavy loading from snow and wind.

There were numerous reports of cracking and whumpfing on the persistent slab mentioned in the problem section over the past several days. This MIN post outlines the issue nicely.

Snowpack Summary

40-60+cm of new snow fell through the weekend with strong southwest and west winds to form reactive storm slabs and wind slabs in alpine lees.

The snow has increased the load on a widespread persistent surface hoar layer. The layer is likely 80-120 cm deep near Renshaw and 60-100 cm deep around Torpy and further north. Reports suggest this layer is most prevalent around treeline elevations, but likely reaches into the alpine and down into the trees too. It may sit above a crust below 1600 m. The likelihood of triggering this layer has likely increased with the new load from the snowfall. For sure the consequence of triggering this layer is high.

There are presently no deeper concerns in the snowpack.

Terrain and Travel

  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • In times of uncertainty conservative terrain choices are our best defense.

Régions couvertes