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Avalanche Forecast

Archived

Dec 6th, 2022–Dec 7th, 2022

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

Regions

North Columbia, South Columbia, Blue River, Clearwater, Clemina, Esplanade, Jordan, North Monashee, North Selkirk, West Purcell, Badshot-Battle, Central Selkirk, Goat, Gold, Kokanee, Retallack, Valhalla, Whatshan.

Westerly wind formed fresh wind slabs in the alpine and at treeline. Choose conservative terrain and consider that hazard may be highest at treeline elevations, where fresh slabs may sit on a 40-80 cm deep persistent weak layer.

Confidence

Low

Avalanche Summary

A weak layer of surface hoar below recent snow has been responsible for the latest snowpack instability. Reports suggest this interface is most prevalent at treeline, between 1700-2000 m, but it was also reported as low as 1450 m.

Saturday: Reports of a reactive snowpack continued throughout the region. From Blue River to Kokanee Glacier, skiers reported whumpfing and cracking. In the Monashees near Revelstoke, shooting cracks were reported as low as 1450 m. Explosives triggered numerous size 2 avalanches failing 50-60 cm down on surface hoar. These avalanches were triggered between 2000-2100 m on north to west aspects.

Sunday: Skier triggered and natural avalanches up to size 2 were reported around treeline on easterly aspects in the south of the forecasting region. They failed on feathery surface hoar about 40 cm deep. In the Revelstoke area, skiers triggered avalanches up to size 2.5 about 40-70 cm deep (see a picture in this MIN report and a more detailed description of the same avalanche in this MIN report). Avalanches were triggered on southerly and north aspects at treeline and in the lower alpine and some were triggered from a short distance away.

Monday: No new avalanches were observed. However, whumpfing and cracking was reported at treeline and below in the Monashees.

Snowpack Summary

Up to 20 cm low-density snow fell on a cold snow surface consisting of feathery surface hoar on shaded aspects and a sun crust on sun exposed aspects.

Buried 40-80 cm deep, a layer of surface hoar, crust, and faceted crystals is the persistent layer of concern. This layer has been most reactive at treeline between 1700-2200 m, but it was also observed as low as 1450 m and widespread whumpfing and cracking was reported throughout the region. In wind exposed areas, the loose snow formed reactive wind slabs over this layer.

Snowpack depths range from 70 cm at treeline to 170 cm in the alpine, with wind-loaded areas exceeding 200 cm.

Weather Summary

Tuesday night

Cloudy with up to 10 cm low-density snow. West wind 30 km/h. Treeline temperature low -12 °C.

Wednesday

Cloudy with a trace of new snow. West wind changing to southwest 25 km/h. Treeline temperature rising to -9 °C.

Thursday

Cloudy, up to 5 cm new snow. Southwest wind increasing to 50 km/h. Treeline temperature rising to -6 °C.

Friday

Mostly cloudy, up to 5 cm new snow. Southwest wind 30 km/h. Treeline high temperature -7 °C.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Expect slab conditions to change drastically as you move into wind exposed terrain.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

Problems

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.

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.