Bulletin d’avalanche

Lizard-Flathead

Jan 5 – 6, 2021Avalanche Canada
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Archivé · expiré 6 years ago

Danger d’avalanche

Thu
Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Points saillants

Human triggered avalanches are likely at higher elevations after a storm crosses the region Monday night.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely - Possible
    Taille
    2–2.5

    The snowpack across the region has some isolated areas where persistent weak layers remain a problem. These layers include feathery surface hoar and/or sugary faceted grains above a hard crust roughly 50 to 100 cm deep. This is a difficult problem to manage because it does not seem to exist in most terrain, but in the isolated places where it does exist it can produce large destructive avalanches.

  • Storm Slabs

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

    Stormy weather on Monday night will create a new storm slab problem. Some natural avalanches may occur in the alpine during the peak of the storm overnight, and then human triggered avalanches will remain likely on Tuesday. With only 10-20 cm of snow expected, the most likely spots for human triggering will be on slopes that have been loaded by wind.

Confidence

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

Weather Forecast

Frontal systems cross the region Monday night and Wednesday afternoon.

MONDAY NIGHT: 10-20 cm of snow, moderate southwest wind, treeline temperatures around -4 C.

TUESDAY: Flurries easing off in the afternoon then some sunny breaks in the afternoon, moderate west wind, treeline temperatures around -6 C.

WEDNESDAY: Scattered flurries throughout the day with 5-10 cm of snow, light southwest wind, temperatures around -4 C.

THURSDAY: Another 5-10 cm of snow by the morning then clearing in the afternoon, light northwest wind, temperatures around-6 C.

Avalanche Summary

The storm over the weekend resulted in a widespread cycle of storm slab avalanches in the Fernie area. This included numerous size 2-3 explosive and naturally triggered avalanches. There was also persistent slab avalanche on Sunday that was remotely triggered in a north facing gully around 1350 m (see the photo here). The avalanche failed on a 50 cm deep surface hoar layer, and illustrates how the current persistent slab problem is lingering in isolated areas.

Watch for fresh storm slabs on Tuesday and keep in mind the potential for surprisingly large avalanches due to the isolated persistent slab problem.

Snowpack Summary

A brief storm crossing the region on Monday night will bring 10-20 cm of snow and southwest wind to create a new storm slab problem at upper elevations. This is falling on top of 30 cm of settled snow from a few days ago. A melt-freeze crust beneath this snow has been reported up to an elevation of 1900 m, but does not seem to be a problem at this point. Around 50 to 100 cm deep, weak layers of feathery surface hoar and/or faceted grains may overly a hard melt-freeze crust. This layer appears to be bonding in certain areas of the region but remains suspect where it is well preserved.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Be careful to keep storm day fever from luring you out into bigger terrain features.
  • Choose slopes that are well supported and have limited consequence.

Régions couvertes