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Avalanche Forecast

Archived

Jan 13th, 2021–Jan 14th, 2021

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

Regions

Kootenay Boundary.

Don't let the sunshine and fresh snow lure you into aggressive terrain. Storm and wind slabs will likely remain reactive to rider triggers, especially where they sit above a persistent weak layer. Use a conservative approach and be aware of overhead hazards like cornices. 

Confidence

Moderate -

Weather Forecast

An upper ridge will build Thursday bringing dryer and sunnier weather.

Thursday/ Friday: A mix of sun and cloud. Alpine temperatures near -2 and freezing levels 1200 m. Ridgetop wind light-moderate from the southwest.

Saturday: Cloudy with some flurries. Light West wind and freezing levels 800 m. 

Avalanche Summary

On Wednesday, a widespread natural avalanche cycle up to size 2.5 was reported on all aspects and elevations. A recent MIN report observed from Rossland also shows a size 3 natural persistent slab avalanche that occurred during or post-storm. 

On Tuesday, explosive control triggered numerous size 2-2.5 slab avalanches and human triggered avalanches up to size 1.5 were also reported. 

Natural and human triggered slab avalanches will continue to exist on Thursday.

Of note, a naturally-triggered size 3 deep persistent slab avalanche released on a southeast aspect at 2200 m in the Rossland range last Tuesday or Wednesday. The avalanche likely failed on the weak layers described in the Snowpack Summary and scrubbed to the ground. 

Snowpack Summary

Up to 40 cm of recent storm snow accompanied by strong to extreme westerly wind has built reactive storm and wind slabs at upper elevations. These slabs may be extra sensitive where they overlie surface hoar in sheltered terrain. Warmer temperatures and a period of rain overnight Tuesday has formed a 3mm surface crust to 1780 m in Kootenay Pass.

Two weak layers are buried in close proximity to one another. They are 70 to 130 cm deep. The layers are composed of surface hoar and faceted grains and they overlie a hard melt-freeze crust. This recent MIN report observed from Rossland on Wednesday the 13th shows good evidence of a large natural slab avalanche failing on the early December persistent layer during or post-storm. This suggests that it remains possible for riders to trigger these layers.

Another layer of faceted grains above a melt-freeze crust that formed in early November is upwards of 200 cm below the surface. This has been the suspected failure layer of a few very large avalanches that released last week in the Rossland range.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Cornice failure may trigger large avalanches.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.