Bulletin d’avalanche

Kootenay Boundary

Mar 3 – 4, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Fri
Sat
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
3 · Marqué
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Points saillants

We are uncertain how buried weak layers in the snowpack will respond to rising temperatures and strong sun. The considerable rating reflects the high likelihood for small loose wet avalanches in many areas and the potential for large persistent slab avalanches in specific areas.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    2–3

    There are a few layers of concern with the first major warm up happening this week.

    1) A spotty layer of small surface hoar crystals is buried 20-40 cm deep around treeline. It won't take long for the warm temperatures to affect the snow this depth. We may see isolated avalanche activity on this layer in the early days of the warm up, but beyond that, the warming will likely help this layer heal.

    2) A persistent weak layer buried 80-150 cm deep is composed of a combination of surface hoar, crusts and facets formed on the surface in late January. The problem seems to be most pronounced in thin snowpack areas on solar aspects. Recently we have seen large explosive loads and storm slab avalanches in motion produce avalanches on this layer. Rapid warming, strong sun or loose wet avalanches could serve as triggers for large, destructive avalanches this week.

    3) Basal facets in shallow snowpack areas in the east of the region could be susceptible to shock from the warm temperatures this week. Extra caution should be exercised in these types of snowpacks. Avalanches on this layer are most likely human triggered from shallow rocky areas, which then propagate out to thicker spots, resulting in large avalanches. 

  • Loose Wet

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

    Loose wet avalanches are most likely on sun exposed slopes and at elevations experiencing above freezing temperatures for the first time. A moist or wet snow surface, pinwheeling or loose wet point releases out of the rocks are good indicators that it is time to back off. Keep in mind that loose wet avalanches can serve as triggers for persistent slabs.

Confidence

Moderate - We are confident the snowpack will rapidly lose strength with the arrival of the forecast weather. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Tuesday night: Clearing. Freezing level 1000 m. Moderate to strong southwesterly wind.

Wednesday: Sunny. Freezing level rising to 2000 m. Moderate southwest wind easing to light.

Thursday: Sunny. Freezing level 2300 m. Light to moderate southwest wind.

Friday: Sunny. Freezing level 2300 m. Moderate to strong southwest wind.

Avalanche Summary

On Monday, pinwheeling and small loose wet avalanches were observed out of steep, rocky solar exposed slopes in the afternoon. Over the weekend, there were a few natural and skier triggered wind slabs size 1.5, along with reports of wind slabs being stubborn to ski cuts. On Saturday, large explosive loads produced size 2-3 results at Kootenay Pass. In thin snowpack areas on solar aspects, a few of these large avalanches are suspected to have stepped down to the January layer described in the snowpack summary.

Snowpack Summary

At upper elevations, 20-40 cm of recent snow has seen significant wind effect, with reports of cross-loaded features and scouring on exposed windward aspects. Around treeline and below, the recent snow may sit over a layer of small surface hoar crystals in isolated areas.

A persistent layer buried 80-150 cm deep is composed of combinations of surface hoar, crusts and facets formed on the surface in late January. The problem seems to be most pronounced in thin snowpack areas on solar aspects. Recently, large explosive loads have been required to trigger an avalanche on this layer. But a rapid rise in temperature such as the one we are currently experiencing can also be a sufficient shock to these types of layers. If they start to become sensitive this week, we could see some large natural and human triggered avalanches.

Shallow snowpack areas in the east of the region may harbor a facetted basal snowpack as described in this MIN report. This structure is often a constant for thin snowpacks and can usually be managed with good travel habits of avoiding shallow rocky areas where the snowpack transitions from thick to thin. This is another layer that could be susceptible to shock from the warm temperatures this week and extra caution should be exercised in these types of snowpacks.

Terrain and Travel

  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Régions couvertes