Bulletin d’avalanche

Lizard-Flathead

Jan 18, 2018Avalanche Canada
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Archivé · expiré 9 years ago

Danger d’avalanche

Fri
Sat
Alpin
4 · Fort
Limite forestière
4 · Fort
Sous la limite
4 · Fort
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Points saillants

Forecast snowfall is uncertain, but fresh storm slabs are set to form over a new weak layer on Thursday. Natural storm slab releases could provide ample triggers for deeper persistent weak layers.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible - Likely
    Taille
    2–3.5
    Large avalanches may be triggered on a number of buried weak layers, even in fairly dense trees and shallow slope angles. Stress on these weak layers will increase as new snow and wind load the snowpack on Thursday.

  • Storm Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely - Very Likely
    Taille
    1–2
    New snow will form fresh storm slabs over a new weak layer on Thursday. The new snow is not expected to bond well and winds may make slabs extra touchy. A small storm slab release could provide enough stress to trigger a deeper persistent weak layer.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Wednesday night: Flurries bringing 3-5 cm of new snow. Strong southwest winds.Thursday: Cloudy with continuing flurries bringing 5-20 cm of new snow. Strong southwest winds. Freezing level to 1700 metres with alpine high temperatures around 0 to -1.Friday: Mainly cloudy. Moderate southwest winds. Freezing level falling to around 1100 metres with alpine high temperatures of -5.Saturday: Mainly cloudy. Moderate southwest winds. Freezing level near the surface with alpine high temperatures around -6.

Avalanche Summary

Very significant avalanche activity occurred in the region last week. Large avalanches ran on multiple persistent weak layers, even in fairly dense trees and low angle slopes. Activity has gradually tapered off, but the potential for human triggering remains. On Tuesday, explosive control in the Lizard range produced a few large persistent slab avalanches on deep weak layers (size 2-2.5). Recent natural activity was also reported in the Sparwood area.

Snowpack Summary

Light new snow amounts have begun to give a thin cover to a new layer of feathery surface hoar on sheltered aspects (especially prominent from 1400-1900 m) as well as sun crust on solar aspects. Recent warm temperatures created this crust and also worked to settle the upper snowpack. Shifting winds during the warm period transported snow from last week, leaving old wind slabs in open terrain as well as cornices along ridges. A number of buried weak layers have been very concerning over the past week, and appear to be gaining strength very slowly. The early January surface hoar layer is around 60 cm below the surface and the unstable weak layer from mid-December (predominantly surface hoar and/or a sun crust) is around 100 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets that developed late-November is near the bottom of the snowpack. All of these layers have been reactive over the past week.

Régions couvertes