Bulletin d’avalanche

Lizard-Flathead

Feb 25 – 26, 2022Avalanche Canada
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Archivé · expiré 5 years ago

Danger d’avalanche

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

Watch for lingering pockets of wind slab on various aspects in exposed terrain and around ridgelines.

There is some recent evidence that the persistent avalanche problem may still be rider triggered in parts of our region.

Problèmes avalancheux

  • Wind Slabs

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

    Watch for pockets of wind slab on all aspects in exposed terrain and around ridgelines due to recent variable winds. 

    Alpine features are the most likely culprits for wind slabs, but exercise some caution in exposed treeline features with stiff snow as well.

    Though wind slabs are becoming more stubborn to trigger, they have formed on top of old crusts and hard wind-pressed snow and with the cold temperatures, they have been slower to heal.

     

  • Persistent Slabs

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

    Persistent slab avalanches are still possible due to a layer of buried surface hoar around 40-60 cm deep. This problem is tricky to pin down because of its spotty distribution (it isn't a problem everywhere). It has been most reactive recently in the Flathead with reports of rider triggering (see MIN post), whumpfing and propagation in snowpack tests.

    Steep, north-facing open treed features that are sheltered from the wind are the most suspect. Check out this post from the field team for the type of terrain we are avoiding.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

THURSDAY NIGHT: Partly cloudy, light southwest wind, alpine low of -16.

FRIDAY: Mix of sun and cloud. Light to moderate southwest wind. Alpine highs of -10.

SATURDAY: Mix of sun and cloud, moderate southwest wind, alpine highs of -7.

SUNDAY: Increasing cloud, moderate southwest wind, alpine highs to -4.

Avalanche Summary

There were small pockets of wind slab triggered by skiers on Wednesday. Also on Wednesday, the South Rockies team experienced whumpfing and cracking in places where the late January surface hoar is still preserved and reactive in snowpack tests, but they didn't see any new avalanches (check out their MIN).

Earlier in the week a skier accidentally triggered a wind slab on a reverse loaded feature in the Lizard Range (MIN here). On Saturday there was a machine triggered avalanche on surface hoar layer in an open gully feature in the Rolling Hills area.

Snowpack Summary

The 10-30 cm of most recent snow has been redistributed by recent variable winds and has built wind slabs in unusual places. In south-facing terrain, new snow sits on top of melt-freeze crusts, and in open terrain recent snow sits over old firm wind-affected surfaces.

A buried surface hoar layer may be found 30-60 cm deep on sheltered, north-facing treeline-type features. This distribution of this layer is spotty in nature but has recently produced avalanches, whumpfing and snowpack test results in the Flathead. 

The lower snowpack is well consolidated, with a crust/facet layer found near the bottom of the snowpack. It is currently considered dormant but could become active later this season. Check out the forecaster blog for more information. 

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Even a small avalanche can be harmful if it pushes you into an obstacle or a terrain trap.
  • Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.

Régions couvertes