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Avalanche Forecast

Archived

Feb 22nd, 2020–Feb 23rd, 2020

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

Regions

Kootenay Boundary.

Storm slabs will build over the day with snowfall and strong wind. Use added caution on steep slopes in open trees, as a slab may rest on surface hoar, particularly in the east of the region. Conservative decision-making is recommended.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

SATURDAY NIGHT: Cloudy with light snowfall, accumulation 1 to 3 cm, light to moderate southwest wind, alpine temperature -6 C.

SUNDAY: Cloudy with snowfall, accumulation 10 to 20 cm, moderate to strong southwest wind, alpine temperature -5 C, freezing level 1200 m.

MONDAY: Mix of sun and cloud with isolated flurries, accumulation 1 to 3 cm, light to moderate northwest wind, alpine temperature -7 C, freezing level 1000 m.

TUESDAY: Partly cloudy, light northwest wind, alpine temperature -7 C, freezing level 800 m.

Avalanche Summary

No new avalanches were observed on Friday. Avalanche activity may increase on Sunday during the stormy conditions.

Snowpack Summary

Storm slabs are expected to build over Sunday with around 10 to 20 cm of snow and strong southwest wind. The snow will accumulate onto a widespread layer of feathery surface hoar crystals or a melt-freeze crust on southerly aspects. The surface hoar was reported as being around 6 to 12 mm in size before being buried.

A 20 to 30 cm thick slab has been reactive to human traffic since last weekend, where the snow overlies another weak layer of surface hoar. The slab has been most reactive in open trees in the eastern part of the region.

The remainder of the snowpack is well-settled.

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Approach steep open slopes at and below treeline cautiously, buried surface hoar may exist.

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.