Bulletin d’avalanche

Lizard-Flathead

Mar 5 – 6, 2021Avalanche Canada
Voir sur la carte
Archivé · expiré 6 years ago

Danger d’avalanche

Sun
Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
Ouvrir la carte complète

Points saillants

Avalanche danger could reach HIGH by the afternoon with sunshine and intense warming. Pay close attention to rising temperatures and the sun's intensity. Stick to simple, low-angle terrain and avoid overhead hazard, especially during the warmest part of the day.

Problèmes avalancheux

  • Cornices

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

    Large cornices exist along ridgelines and require a wide berth from above and below. The likelihood of them becoming weak and failing is greater with warming and solar radiation. They have the potential to trigger slab avalanches from slopes below. 

    West to southwest wind has formed pockets of wind slab on leeward slopes. These could be triggered by the weight of a skier or rider, especially on east-northeast aspects. 

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    2–3

    Two layers of concern exist and have been reactive over the past couple of days. The upper layer is down 30-50 cm and has recently failed primarily on a sugary facet interface. The deeper layer of concern is down 60-100 cm. This layer consists of surface hoar, faceted grains, and/or a melt-freeze crust. The layer has been most problematic around treeline elevations and in openings below treeline, but also reaches into the lower alpine. 

  • Loose Wet

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

    Wet loose avalanches are likely when the sun comes out and freezing levels rise. Watch for signs of warming and snowpack instability such as rolling snowballs, moist snow and natural avalanche activity. 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

THURSDAY NIGHT - Mainly clear / moderate to strong southwest wind / alpine low temperature near 1 / freezing level 2400 m

FRIDAY - Sunny / moderate to strong southwest wind / alpine high temperature near 4 / freezing level 2400 m

SATURDAY - Sunny in the morning and increasing cloud cover in the afternoon / moderate to strong southwest wind / alpine high temperature near 2 / freezing level 2400 m, dropping to valley bottom overnight 

SUNDAY - Mainly cloudy with flurries / moderate southwest wind / alpine high temperature near -3 / freezing level 1500 m

Avalanche Summary

On Thursday, at the time of publishing, there were several reports of natural loose wet avalanches up to size 1.5 and natural wind and wet slab avalanches up to size 2. There were also a few reports of size 2.5 natural persistent slab avalanches in the nearby Waterton National Park region.

On Wednesday there were several reports of natural size 1 wet loose avalanches on solar aspects in the afternoon.

Sun and warm temperatures are our primary concern over the next few days. 

  • Large cornices may weaken and fail, triggering slabs on the slopes below. 
  • Wet loose avalanches will likely be seen from solar aspects first and then possibly all aspects. 
  • The persistent slab sitting above weak layers may stiffen and consolidate further, failing as a natural avalanche or becoming more sensitive to skier and rider triggers. 
  • Pockets of wind slab may be reactive on northeast-east aspects at upper elevations. 

Snowpack Summary

Strong southwest to west wind has formed wind slabs on leeward slopes while freezing rain formed a widespread breakable crust on the surface below about 1800 m, and in spotty locations at upper elevations. 

Up to 50 cm of snow sits above a variety of old interfaces that formed in mid-February. There is 60-100 cm sitting on a persistent weak layer that was buried in late January. These interfaces are mostly made up of sugary facets, hard wind pressed surfaces, surface hoar in wind-sheltered locations, and sun crust on steep solar aspects. Recent test results indicate that the late January persistent weak layer is potentially still quite reactive.

Terrain and Travel

  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.

Régions couvertes