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Avalanche Forecast

Archived

Jan 11th, 2012–Jan 12th, 2012

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

Regions

Kootenay Boundary.

Confidence

Good - -1

Weather Forecast

Thursday: Dry and clear, with freezing levels near valley bottoms and moderate northwesterly winds. Friday: Increasing cloud in the afternoon with freezing levels briefly rising as high as 1500m. Saturday: Light snowfall with freezing levels around 900m.

Avalanche Summary

Recent observations include a slope-cut Size 1.5 20-40cm thick slab avalanche that ran on the mid-December persistent weakness where it was found to be facets on a very steep shallow rocky unsupported roll. Other reports include a few small natural avalanches from recent wind loading in cross-loaded treeline features, and skiers hucking pillows and cliffs on open slopes below treeline were triggering small 20-30cm thick soft slabs suspected to involve surface hoar buried early January. Finally, low density surface snow is sluffing readily in steep terrain.

Snowpack Summary

Warm temperatures and light precipitation settled the 20-40cm of recent storm snow and created upside down slabs and/or thin surface crust on Monday. Since then, light amounts dry snow is maintaining the snow supply for wind slab development, cold temperatures are likely starting to improve storm slab stability, and surface hoar is growing. A thin melt/freeze crust can be found in the upper snowpack as high as 1900m, and some areas are reporting surface hoar buried early-January now down 10-30cm. The late-December interface is now down 30-60cm and producing moderate to hard resistant snowpack test results. While the mid-December surface hoar/facet persistent weakness, down 40-100cm, is producing anywhere from easy to hard results, but consistently shows a high propensity to propagate fractures. Recent whumpfing suggests basal facets remain concern in shallow snowpack areas especially with heavy triggers in thin spots, and weaknesses in the slab above create the potential for step-down avalanches.

Problems

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.

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.