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Avalanche Forecast

Archived

Apr 26th, 2023–Apr 27th, 2023

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

Regions

Northwest Coastal, Northwest Inland, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson, Kispiox, Microwave-Sinclair, Ningunsaw, Ningunsaw, South Bulkley, South Bulkley, Telkwa.

Wintry conditions are found in the alpine, whereas spring-like problems are prominent at lower elevations. Travel cautiously and be aware of the various avalanche problems you could come across.

Confidence

Moderate

Avalanche Summary

Numerous human-triggered persistent slab avalanches have occurred on the layers described in the Snowpack Summary over the past few weeks. Continue diligent terrain travel to limit your exposure to this avalanche problem.

The likelihood of seeing very large avalanches releasing on the deeply buried weak layer near the base of the snowpack as described in the Snowpack Summary will increase with each day of warming. This is particularly true for days without an overnight surface refreeze. Humans are most likely to trigger these layer in steep and rocky slopes where the layer is closer to the snow surface.

Avoiding cornice exposure is also a good idea, as they are very large and could fail naturally or under the weight of a human.

Snowpack Summary

Wind and storm slabs may have formed during Tuesday night's storm. This new snow overlies a melt-freeze crust on all aspects up to 1300 m and to ridgetop on sun-exposed slopes.

Various layers of surface hoar, facets, and crusts may be found around 50 to 150 cm deep in coastal areas and 30 to 50 cm in shallower snowpack areas in the north and east of the region.

Weak faceted grains may exist near the base of the snowpack, particularly in shallower snowpack areas.

Cornices are large and looming at this time of year and will weaken with daytime warming.

Weather Summary

A cool and cloudy Thursday is expected with the freezing level around 1000 m and moderate southwest winds. Freezing levels are on the rise for Friday and into the weekend, ranging from 2000 m to 3300 m. A mix of sun and cloud is generally expected, with cloudy skies and rain on Sunday.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Use small low consequence slopes to test the bond of the new snow.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Cornice failures could trigger very large and destructive avalanches.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.