Bulletin d’avalanche

Purcells

Jan 27 – 28, 2023Avalanche Canada
Voir sur la carte
Archivé · expiré 4 years ago

Danger d’avalanche

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

Points saillants

Triggering a slab or getting even smaller amounts of loose snow moving could result in a widespread destructive avalanche if buried weak layers are affected by the increased load.

Be careful when transitioning into wind-affected terrain and keep the deep persistent problem at the forefront of your decision-making process.

Fresh tracks are best enjoyed on low-angle low consequent terrain today.

Problèmes avalancheux

  • Persistent Slabs

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

    The top metre of the snowpack holds a couple of weak layers which are at depths that can be triggered by human activity. Down 20 to 40 cm from the surface there is a surface hoar layer that was buried in early January. Below this, down 40 to 70 cm from the surface there is a layer made of surface hoar, facets and or a crust that us from December.

    Smaller avalanches could create a "domino effect" and create large avalanches that encompass massive areas.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    1–1.5

    Incoming snow will be sitting on a variety of surfaces that include wind slabs at higher elevations. This incoming snow will continue to bury weaker layers that can be found just below the surface which have the potential to be triggered. Wind will be redistributing this new snow into deeper pockets primed for human triggering.

  • Deep Persistent Slabs

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

    A weak layer near the base of the snowpack, buried in November, has been recently reactive in the Dogtooth Range . Human and natural triggering of this layer remains possible, especially in shallow areas with variable snow depths.

Confidence

Moderate

Avalanche Summary

Wednesday saw a range of avalanches that varied and size, characteristics, and what it was that triggered them. Wind slabs and deep persistent, with some avalanches having a combination of both, were the main culprits. They were between size 1 to 2.5. Most were natural avalanches but some explosive work on cornices that are beginning to be a problem also produced avalanches.

On Tuesday there was a report of a size 3.5 natural avalanche in the Dogtooth Range. This was likely a deep persistent avalanche with a wide propagation triggering near ridgetop at the upper end of treeline on an easterly aspect.

On Monday there was a size 3 skier triggered a deep persistent avalanche on an east aspect starting at 2300 m in the Terminator area in the Dogtooth Range. This MIN outlines the avalanche.

Skiers on Saturday were surprised by a size 2 avalanche that slid on deeply buried surface hoar. What was most surprising about this avalanche was how little of an angle it occurred on. Our persistent slab problem and deep persistent slab problem are still problems.

Snowpack Summary

New snow arriving Thursday night and into Friday will be surface hoar and/or wind slabs. The surface hoar can be found developing on most elevations and aspects in the western and northern parts of our region. While the wind slabs can be found in exposed areas at higher elevations.

The mid-snowpack contains a couple of layers of major concern. The first is down 30 to 50 cm and is a layer of surface hoar from early January. The second is a layer of surface hoar, facets, and crust created in December and found 40 to 60 cm down. The surface hoar is most prevalent in sheltered areas while crusts and any associated faceted snow are more widespread.

The bottom of the snowpack is weak and faceted and contains a weak layer from late November. The total depth of this weak and shallow snowpack ranges between 80 and 180 cm at treeline and is shallowest in the eastern part of our region.

Weather Summary

Thursday Night

Cloudy, up to 8 cm accumulation focused mainly in the west, wind southwest 13 km/h gusting to 40, treeline temperatures at -6 C with freezing level climbing to 1500 m.

Friday

Mostly cloudy, 4 to 12 cm accumulation, wind northwest 20 km/h, treeline temperatures -5 C.

Saturday

Mainly sunny, trace accumulation early in the morning, wind northest 15 km/h, treeline temperatures falling to -18 C.

Sunday

Sunny with cloudy periods, no accumulation, winds north 20 km/h, treeline temperatures -23 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Watch for changing conditions today, storm slabs may become increasingly reactive.
  • Uncertainty is best managed through conservative terrain choices at this time.
  • Avoid areas with overhead hazard.
  • Be carefull around freshly wind loaded features.
  • Choose slopes that are well supported and have limited consequence.

Régions couvertes