Bulletin d’avalanche

Northwest Coastal

Mar 18 – 19, 2022Avalanche Canada
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Archivé · expiré 5 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

Variable weather across the region has created different avalanche problems in different areas. Diligently gather snowpack information before choosing your line, or stick to mellow terrain. See our current forecasters' blog for more info.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Very Likely
    Taille
    2–3.5

    This layer has been most active at treeline elevations, but may extend into the low alpine, and upper below treeline. 

    Two snowpack characteristics are required for this to be an avalanche problem in your area. 

    • a layer of preserved, feathery surface hoar crystals. (40-120 cm below the snow surface)
    • a dense slab sitting on top of the weak layer. (most likely on slopes that were loaded by wind over the last week)

    Avoiding this problem will require extensive knowledge of the snowpack in your area. Be very diligent in your information gathering, or stick to simple, low consequence terrain. Signs of instability like whumpfs, shooting cracks, and recent avalanches are all cues to retreat to mellower terrain.  

    Spread out while travelling to avoid exposing multiple people to a suspect slope. Consider the terrain that is above you, as this layer may trigger remotely. 

  • Storm Slabs

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

    Snowfall has varied greatly throughout the region, recent storm snow may still avalanche under the weight of a rider. Start with small, low consequence slopes, and test the bond of the most recent snow before moving into bigger terrain. 

Confidence

Moderate - Recent weather patterns have resulted in a high degree of snowpack variability within the region.

Weather Forecast

Unsettled weather continues with light snowfall. Heavier snowfall is forecasted for the immediate coast and further up some inlets, but it is looking unlikely that it will push very far inland.

FRIDAY NIGHT: Mostly cloudy. 3-8 cm of snow expected. Moderate southwest ridgetop wind. Freezing level falls to around 500 m. Alpine low around -6 °C.

SATURDAY: Partly cloudy. 0-5 cm of snow expected. Light to moderate southwest ridgetop wind. Freezing level down to 500 m overnight, and rising to 750 m through the day. Alpine high around -4 °C.

SUNDAY: Partly cloudy. 2-10 cm of snow expected. Moderate south ridgetop winds, trending to strong in the afternoon. Freezing level at valley bottom overnight, rising to 600 m through the day. 

MONDAY: Mostly cloudy. 5-10 cm of snow expected, with another trace through the day. Strong southwest ridgetop winds. Freezing level rising to 1400 m. 

Avalanche Summary

On Thursday and Friday, northwest of Terrace, large to very large avalanches were being triggered by riders and vehicles. These avalanches:

  • were failing on a layer of fairly large (10 mm), weak, feathery, surface hoar crystals that were buried early in March.
  • were occuring mostly on Northeast facing slopes around treeline.
  • were easily triggered, and propagating long distances.
  • were failing 60-100 cm deep.

On Thursday, west of Terrace, where heavier snow and rainfall has continued, small, naturally triggered dry loose avalanches were reported in the high alpine, as well as a large glide slab avalanche at treeline. 

Snowpack Summary

35-80cm of recent snow has fallen, with strong southwest winds creating deeper deposits on east facing aspects. Low elevations may hold 10-30 cm of wet/moist snow sitting over a widespread crust on all aspects below 1200 m.

50-100 cm below the snow surface, a weak layer of feathery surface hoar crystals could be preserved in sheltered terrain at and above treeline. This weak layer has started producing large avalanches, mostly north and west of Terrace, where moderate to heavy snowfall and wind have continued through the week. In areas further inland, where the storm tapered off earlier, this layer may not be at its tipping point, but I'd still be suspicious of it through the weekend. 

A thick rain crust from mid-February is buried 100-150 cm. The snowpack below is well consolidated.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Start with conservative lines and watch for clues of instability.
  • Be careful as you transition into wind affected terrain.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Surface hoar distribution is highly variable. Avoid generalizing your observations.

Régions couvertes