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Avalanche Forecast

Archived

Jan 28th, 2021–Jan 29th, 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 possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Kootenay Boundary.

The recent snow has added load to buried weak layers and fresh storm slabs will likely be reactive to human triggers in many areas. Conservative terrain selection is recommended.

Confidence

Moderate - Uncertainty is due to how quickly the snowpack will recover and gain strength.

Weather Forecast

THURSDAY NIGHT - Flurries, 5-10 cm / light to moderate southwest wind / alpine low temperature near -6

FRIDAY - Mainly cloudy with isolated flurries / light to moderate southwest wind / alpine high temperature near -5 

SATURDAY - Mainly cloudy with a few flurries, up to 5 cm / light to moderate southwest wind / alpine high temperature near -6 

SUNDAY - Flurries, 5-10 cm / moderate to strong southwest wind / alpine high temperature near -4

Avalanche Summary

With up to 50 cm of new snow sitting on potential weak layers, storm slabs are expected to be easy to trigger on Friday.

There were numerous reports of natural and explosives triggered size 1-2 storm slab avalanches on Thursday.

A few size 1 storm slab avalanches were reported in the region on Wednesday.

Snowpack Summary

25-50 cm of new snow sits on firm wind slabs in exposed areas, on a melt-freeze crust in many areas around treeline and below treeline, on a sun crust on steep south-facing slopes, and on large surface hoar in sheltered areas.

There are potentially several more layers of surface hoar in the upper snowpack, with the most notable one down about 50-70 cm. This layer was buried in early January.

A couple of crusts surrounded by weak faceted grains are buried deep within the snowpack. The upper layer is 80 to 130 cm deep and the lower one is near the ground. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for loose avalanches in steep terrain where snow hasn't formed a slab.

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.