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Avalanche Forecast

Archived

Dec 4th, 2022–Dec 5th, 2022

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

Pay attention if the wind picks up - reactive slabs may form quickly over weak surface hoar. Choose conservative terrain and consider that hazard may be highest at treeline elevations.

Confidence

Low

Avalanche Summary

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

Wednesday: a natural avalanche cycle size 2-3 was reported in both the Selkirks and Monashees north of Revelstoke. Whumpfing and cracking were reported throughout the region.

Thursday and Friday: Widespread reports of whumpfs and cracks continued, and included a size 2 avalanche remote triggered by skiers in the Selkirks south of Revelstoke.

Saturday: a reactive snowpack continued to be reported throughout the region on Saturday. From Blue River to Kokanee glacier skiers reported whumpfs and cracking. In the Monashees near Revelstoke, shooting cracks were reported as low as 1450 m.

As well on Saturday, 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.

Snowpack Summary

Low-density flurries have dusted localized areas overnight and cold temperatures and starry skies are promoting surface hoar growth and facetting.

Buried 40-70 cm, a layer of surface hoar, crust, and faceted crystals is the persistent layer of concern. This layer has been most reactive between 1700-2200 m, but reported as low as 1450 m with widespread whumpfing and cracking reported around the region. Cold temperatures and little wind have limited slab development over this layer, this could quickly change as wind increases with plenty of low-density snow available for transport.

Snowpack depths range from 70 cm at treeline to 150 cm in the alpine, with wind-loaded areas exceeding 200 cm.

Weather Summary

Sunday night

Clear with patchy cloud, possible inversion and valley fog forming. Northeast wind 10-25 km/hr. Treeline temperature low -22 °C

Monday

Increasing cloud and isolated flurries, trace accumulation. Southwest wind 10-20 km/hr. Treeline high temperature -16 C.

Tuesday

Increasing cloud and isolated flurries, trace to 5 mm accumulation, high snow-to-liquid ratios could produce enhanced snowfall at upper elevations. West wind 15-25 km/hr. Treeline high temperature -12 C.

Wednesday

Cloudy, windy, and flurries, up to 10 mm accumulation forecast (cold, low-density snow). Southwest wind gusting upwards of 40 km/hr. Treeline temperature rising to -8 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.
  • Keep in mind that human triggering potential persists as natural avalanching tapers off.
  • Carefully monitor the bond between the new snow and old surface.

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.