Bulletin d’avalanche

Lizard-Flathead

Jan 31 – Feb 1, 2020Avalanche Canada
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Archivé · expiré 7 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

A wet and warm weather system is headed for the region. Expect to find increasingly reactive storm slabs as snow falls with strong winds and rising temperatures.

Problèmes avalancheux

  • Storm Slabs

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

    Snow falling with strong winds and rising temperatures will develop an increasingly reactive storm slab problem through the day. Expect to find the most reactive deposits in open areas, around ridge features, and lee terrain - places where wind has redistributed loose snow. Rain and rising freezing levels will encourage loose-wet avalanches at lower elevations as freezing levels rise and the snowpack warms.

  • Deep Persistent Slabs

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

    Facetted, weak snow at the base of the snowpack is a cause for concern with forecasted weather. Rapid loading from new snow and wind or rapid warming from rising freezing levels or rain can stress previously inactive weak layers in the snowpack. If this layer "wakes up" with increasing load and temperatures, it will produce large and destructive avalanches.

Terrain and Travel

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • Watch for wind-loaded pockets especially around ridgecrest and in extreme terrain.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.

Confidence

Moderate - Uncertainty is due to the track & intensity of the incoming weather system.

Weather Forecast

Thursday night: Cloudy with isolated flurries, up to 10 cm. Alpine low temperature -7 C. Moderate southwest winds.

Friday: Mix of sun, cloud and flurries, 10-20 cm. Alpine high temperature +2 C. Moderate to strong southwest winds. Freezing level rising to 2000 m.

Saturday: Flurries and snow, 10-30 cm. Alpine high temperature 0 C. Moderate southwest wind gusting to extreme. Freezing level 1900 m.

Sunday: Mix of sun, cloud, and isolated flurries. Alpine high temperature -9 C. Light southwest wind gusting to strong. Freezing level dropping to valley bottom.

Avalanche Summary

On Wednesday, explosives triggered avalanches to size 2 within the recent storm snow.

Last weekend and early this week, there were reports of natural, human-triggered, and explosive triggered avalanches up to size 2.5 breaking in the new storm snow, specifically where it was drifted by wind into stiffer slabs on northwest through northeast aspects. A couple of these avalanches have been reportedly triggered by cornice fall. See this MIN report for a helpful illustration of these wind slab avalanches.

Snowpack Summary

Southwest winds have impacted 20-40 cm recent snow producing slabs in the alpine and exposed tree line areas and building reactive cornices. The recent snow covers a temperature crust which formed Friday up to 1600 m and higher elevations solar features.

The stout upper snowpack continues to settle in mild temperatures. Several crust layers exist in the mid-pack as a result of previous warming and rain events. These have not been identified as bed surfaces or failure planes in recent avalanche activity. The bottom 10-20 cm of the snowpack consists of faceted snow and decomposing crusts. Although inherently weak, this basal layer has not been an active avalanche problem in the region since December.

Régions couvertes