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Avalanche Forecast

Archived

Dec 23rd, 2022–Dec 24th, 2022

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

Regions

Kootenay Boundary, Bonnington, Grohman, Kootenay Pass, Norns, Rossland, Ymir, Kokanee, Retallack, Valhalla.

Stick to conservative terrain as the storm slab problem becomes trickier on Saturday, moderate to heavy snowfall is expected.

With several buried persistent weak layers expected to become more reactive as snowfall accumulates, step down avalanches are increasingly likely.

Confidence

Moderate

Avalanche Summary

A cycle of natural wind slab avalanches to size 1.5 was observed on Thursday morning, driven by the moderate to strong southeast winds. Two size 2 skier accidentals were also reported in north facing wind affected features, failing on the mid December surface hoar. Read about their decision making after triggering the first avalanche here.

On Tuesday and Wednesday several size one skier triggered wind slab avalanches were reported. These avalanches were on easterly aspects at upper treeline.

Snowpack Summary

The snowpack is becoming increasingly complex with several deeper instabilities that may persist through the season. Sustained cold temperatures have continued to facet (weaken) the snowpack.

At the surface, storm snow is being redistributed into wind loaded features in treeline and alpine terrain. These new slabs will form over facets, surface hoar or a crust.

Several more layers of concern exist in this snowpack:

  • An early December layer of surface hoar in sheltered areas and a thin sun crust in open south-facing terrain is buried approximately 30-50 cm deep. This layer has recently produced surprising avalanches in upper treeline and lower alpine terrain features.

  • The most concerning layer buried in mid November is made up of large surface hoar crystals, facets, and a melt-freeze crust and can be found up to 80 cm deep. This layer has been reactive at treeline between 1700 to 2200 m, on all aspects.

Weather Summary

Cold arctic air begins to weaken and move out of the area on Saturday, as a warm Pacific low pushes moderate snowfall and strong winds into the interior this week.

Friday Night

Cloudy with up to 5cm of new snow expected. Moderate southwest winds continue overnight. Freezing level below valley bottom.

Saturday

Stormy with 15-30 cm of new snow expected, favoring terrain south of Nelson and the Valhallas. Strong southwest winds and a high of -12°C.

Sunday

Cloudy with trace amounts of new snow expected. Moderate northwest winds with a high of -10°C.

Monday

Moderate to heavy snowfall returns. Temperatures warming to or above 0°C as freezing levels rise to 800 m.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

  • Watch for fresh storm slabs building throughout the day.
  • Use increased caution at all elevations. Storm snow is forming touchy slabs.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for larger than expected storm slabs due to the presence of buried surface hoar.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.