Bulletin d’avalanche

Lizard-Flathead

Feb 28 – Mar 1, 2022Avalanche Canada
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Archivé · expiré 5 years ago

Danger d’avalanche

Wed
Thu
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
3 · Marqué
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Points saillants

Avalanche danger will increase throughout the day with heavy snowfall, southwest wind and rising freezing levels. 

Avoid avalanche terrain during periods of heavy loading from new snow and wind.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1.5–3

    Persistent slab avalanches are still possible due to a layer of buried surface hoar that was around 40-60 cm deep before this storm. 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.

    Smaller storm avalanches have the potential to step down to these deeper layers in sheltered north-facing treed terrain.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    1–3

    Ongoing snowfall, southwest wind and rising freezing levels will combine to make dangerous avalanche conditions as the day progresses. Storm slabs will become increasingly sensitive to human triggering and a natural avalanche cycle will begin as snow stacks up. Avoiding avalanche terrain and staying clear of overhead hazard is the best way to stay safe during periods of heavy snow accumulation.

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

There is some model disagreement around the timing and intensity of the next system. 

Sunday night: Snowfall 5-10 cm, moderate southwest wind, treeline low around -5 °C.

Monday: Snowfall 20-35 cm, moderate to strong southwest wind, rising freezing levels, treeline high around -1 °C.

Monday night: Heavy snowfall possible (up to 50 cm), moderate to strong southwest winds, freezing levels rising into Tuesday morning.

Tuesday: Precipitation continues with 10-15 mm, moderate to strong southwest wind, freezing levels hovering around 2000 m. 

Wednesday: Light snow, light to moderate southwest wind, freezing levels around 1700 m.

Avalanche Summary

On Saturday the wind triggered some small dry loose avalanches and wind slabs were starting to form again in spill zones. No new avalanches were reported on Thursday or Friday. On Wednesday, skiers were triggering small wind slabs. The Avalanche Canada field team reported whumpfing and cracking in places where the late-January surface hoar is still preserved and reactive, but they didn't see any new avalanches.

Last Saturday, there was a machine-triggered persistent slab avalanche on a surface hoar layer in an open gully feature in the Rolling Hills area.

Snowpack Summary

New storm snow will build slabs on a variety of old surfaces like recent wind slabs, sun crusts on south-facing terrain, and cold weak crystals on shaded aspects. 

A buried surface hoar layer that was 30-60 cm deep before the storm can still be found on sheltered, north-facing treeline-type features. This distribution of this layer is spotty in nature but has produced avalanches and snowpack test results in the past week, mostly in the Flathead. While it does not appear to be as widespread or reactive in the Lizard Range, it has been found in some locations. 

The lower snowpack is well consolidated, with a crust/facet layer from early-December 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

  • Storm slab size and sensitivity to triggering will likely increase through the day.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.

Régions couvertes