Bulletin d’avalanche

Lizard-Flathead

Feb 23 – 24, 2022Avalanche Canada
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Archivé · expiré 5 years ago

Danger d’avalanche

Fri
Sat
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
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Points saillants

Recent reverse loading from northeast winds have formed wind slabs in unusual places. There is uncertainty about how quickly slabs will bond to old surfaces like melt-freeze crusts and hard wind-pressed snow. 

Problèmes avalancheux

  • Wind Slabs

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

    Watch for pockets of wind slab on various aspects in exposed terrain and around ridgelines. The storm initially came in with southwest winds, but with the intrusion of arctic air, winds switched to the northeast potentially building slabs in less common locations.

    These slabs have formed on top of old crusts and hard wind-pressed snow and there is uncertainty about how quickly they will bond to old surfaces. 

     

  • Persistent Slabs

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

    Persistent slab avalanches are possible mostly on shaded aspects due to a layer of buried surface hoar around 40-50 cm deep. The nature of this problem is tricky because of its spotty distribution and the presence of various crusts above it on some aspects. It has been most active recently in the Flathead and there is some evidence (see MIN post) it can still be triggered in sheltered open treed features. 

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

TUESDAY NIGHT: Mostly clear, winds light to moderate from the northeast. Alpine low -27.

WEDNESDAY: Mostly sunny with increasing afternoon cloud. Light northwest to southwest winds. Alpine high of -16. 

THURSDAY: Light flurries possible overnight Wed/Thurs. Partly cloudy, light north wind, alpine high of -10.

FRIDAY: Mix of sun and cloud. Light southwest wind and alpine highs of -10.

Avalanche Summary

On Monday a skier accidentally triggered a wind slab on a reverse loaded feature in the Lizard Range (MIN here). There were other reports of small natural and skier-controlled wind slabs in the region on Monday as well. On Saturday there was a machine triggered avalanche on an old buried surface hoar layer in an open gully feature in the Rolling Hills area.

Snowpack Summary

The 5-15 cm of most recent snow has been redistributed by moderate to strong northeast winds and has formed 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 30-50 cm deep on sheltered, north-facing treeline-type features. This layer has become significantly less reactive and harder to find, but it can still catch riders off guard in isolated areas. Check out this recent MIN from the Rolling Hills area for an example.

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.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Be aware of the potential for large avalanches due to the presence of buried weak layers.

Régions couvertes