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Avalanche Forecast

Archived

Jan 17th, 2022–Jan 18th, 2022

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Coastal.

Assess for wind slabs prior to committing to terrain with high consequence.

Confidence

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

Weather Forecast

MONDAY NIGHT: Clear skies with no precipitation, 20 km/h north wind, alpine temperature -6 C.

TUESDAY: Partly cloudy with no precipitation, 10 km/h north wind, alpine temperature -7 C.

WEDNESDAY: Cloudy with snowfall, accumulation 10 cm, 60 km/h southwest wind, alpine temperature -5 C.

THURSDAY: Cloudy with snowfall, accumulation 20 to 40 cm, 60 km/h southwest wind, alpine temperature -3 C, freezing level 800 m.

Avalanche Summary

Many large avalanches were triggered naturally and by explosives on Sunday and Monday, with substantial entrainment of wet snow at lower elevations. Storm slabs were most prominent above around 1200 m and wet avalanches below. 

Avalanche activity is anticipated to decrease on Tuesday with cooler weather.

Snowpack Summary

Around 30 cm of recent snow fell above 1200 m with associated strong wind from the southwest to northwest, which formed wind slabs in lee terrain features in wind-exposed terrain. Below around 1200 m, the precipitation mostly fell as rain, which will freeze into a hard melt-freeze crust.

A weak layer of faceted grains and/or surface hoar may be found about 50 to 100 cm deep, formed late December to early January. This layer was the culprit of avalanche activity last week in the north of the region.

The remainder of the snowpack is mostly strong in the south of the region. In the north, the base of the snowpack consists of faceted grains around a melt-freeze crust, which is currently dormant.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Avoid freshly wind loaded terrain features.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.