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Avalanche Forecast

Archived

Dec 27th, 2024–Dec 28th, 2024

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

Regions

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

There's cause for concern in the south as accumulations on weak layers catch up with the north, where persistent slabs are already active. Manage uncertainty with low consequence terrain.

Confidence

Moderate

Avalanche Summary

A MIN report from the Shames area on Wednesday describes wind slab formation and reactivity to skier traffic that helped confirm active conditions near Terrace.

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. Roughly half this amount accumulated on Wednesday through Thursday and has fed into new wind slab development. You'll likely 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 early December crust down 50 to 90 cm. Recent observations of these layers in the Terrace area are limited. They are a pronounced problem in the north.

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

Weather Summary

Friday Night

Cloudy with continuing flurries bringing a trace to 5 cm of new snow. 10 to 25 km/h south ridgetop wind, easing. Freezing level falling from 800 m to 500 m.

Saturday

Mainly cloudy with isolated flurries. 5 to 15 km/h east ridgetop wind. Freezing level to surface with treeline temperature falling to -5 °C.

Sunday

Mainly sunny. Calm to 5 km/h variable ridgetop wind. Treeline high temperature around -4 °C

Monday

A mix of sun and cloud. 5 to 10 km/h variable ridgetop wind. Treeline high temperature -5 °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.
  • Start with conservative terrain and watch for signs of instability.
  • 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.