Bulletin d’avalanche

Lizard-Flathead

Dec 16 – 17, 2022Avalanche Canada
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Archivé · expiré 4 years ago

Danger d’avalanche

Sun
Mon
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Watch for fresh wind slabs forming on atypical aspects at ridgetop as upper level wind picks up from the northwest.

We have uncertainty around the reactivity of a buried weak layer that produced large rider-triggered avalanches last weekend. Read our latest blog for advice on how to manage a persistent slab problem.

Problèmes avalancheux

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    As ridgetop winds pick up from the northwest, watch for fresh wind slabs forming in atypical terrain features due to reverse-loading.

  • Persistent Slabs

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

    A layer of surface hoar buried 30-50 cm deep has shown propagation in recent snowpack tests.

    Layers of surface hoar and facets, buried 80-90 cm deep, were reactive to human triggers at treeline elevations last weekend.

Confidence

Low

Avalanche Summary

Earlier this week, avalanche observations were mostly limited to small, explosive-triggered wind slabs.

Last weekend, there were several alarming reports of large (size 2-3) persistent slab avalanches. They were remotely triggered by skiers or snowmobiles at treeline elevations. Check out these MIN reports here and here. A huge thank you to the groups who shared their observations to the Mountain Information Network!

Snowpack Summary

A thin surface crust may be found on steep south aspects. 5-10 cm of recent snow rests over a layer of surface hoar at treeline and below. Near ridgetop, the recent snow is likely being reverse-loaded into atypical terrain features as upper level northwest winds pick up on Friday.

A well settled upper snowpack may overlie a layer of surface hoar formed in early December, now buried 30-50 cm deep.

A concerning weak layer consisting of facets and surface hoar formed in November is now buried 80-90 cm deep. At the bottom of the snowpack, a thick crust sits on the ground.

At treeline, snowpack depths vary from 120 to 200 cm.

Weather Summary

Thursday night

Partly cloudy. Ridgetop wind light to moderate west. Alpine low -14 C.

Friday

Mix of sun and cloud. Ridgetop wind moderate northwest. Alpine high -11 C.

Saturday

Around 5 cm new snow. Light southwest wind. Alpine high -9 C.

Sunday

Mix of sun and cloud with isolated flurries. Light to moderate southwest wind. Alpine high -20 C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Avoid open slopes and convex rolls at and below treeline where weak layers may be preserved.
  • In times of uncertainty conservative terrain choices are our best defense.

Régions couvertes