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Avalanche Forecast

Archived

Dec 28th, 2024–Dec 29th, 2024

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

Regions

Northwest Coastal, Boundary, Kitimat, Nass, Rupert, Seven Sisters, Shames, Stewart, Howson, Microwave-Sinclair.

Seek out sheltered snow to avoid wind slab problems but approach any avalanche terrain with caution. A problematic persistent slab structure exists in much of the region's snowpack.

Confidence

Moderate

Avalanche Summary

No avalanches have been observed in the south of the region since a report of reactive wind slabs at Shames on Wednesday.

In the north of the region, simultaneous remote-triggered size 2.5 and size 2 persistent slabs were seen Thursday, triggered from 150 m away. They fit a pattern of increasing persistent slab activity up north, where natural avalanches up to size 3 failing on the early December crust have been focused around northwest aspects in the alpine.

Snowpack Summary

Up to 60 cm of recent snow overlies previously wind affected surfaces in the alpine and at treeline. You may find moist surface snow or thin accumulations on crust below 900 m.

Below these surface layers, two distinct weak layers exist in the top meter of the snowpack. A layer of facets and/or surface hoar down 30 to 50 cm and the more prominent early December crust down 50 to 90 cm. Observations of these layers in the Terrace area are limited, but snowpack tests by the field team produced easy, sudden results in facets on the crust 60 cm deep in the Ashman area on Friday. This structure is an active problem in the north of the region.

Treeline snow depth range from 200-280 cm. The lower snowpack has no layers of concern.

Weather Summary

Saturday Night

Cloudy with flurries bringing up to 5 cm of new snow. 5 to 30 km/h southeast ridgetop wind, increasing. Freezing level to surface.

Sunday

A mix of sun and cloud. Calm to 10 km/h variable ridgetop wind. Treeline high temperature around -4 °C

Monday

A mix of sun and cloud. 5 to 15 km/h variable ridgetop wind. Treeline high temperature -5 °C.

Tuesday

Mainly cloudy with isolated flurries. 30 to 40 km east or southeast ridgetop wind, increasing. Treeline high temperature -6 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
  • Be aware of the potential for large avalanches due to buried weak layers.
  • Avoid steep, rocky, and wind-affected areas where triggering slabs is more likely.

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.