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Avalanche Forecast

Archived

Mar 5th, 2013–Mar 6th, 2013

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

Confidence

Good

Weather Forecast

Tonight and Wednesday: A low pressure system moves inland to the South of the border. Light-moderate precipitation will begin this evening over the Southern ranges. Ridgetop winds light from the SE. Alpine temperatures near -5 and freezing levels 1300 m. Thursday: Mainly cool and dry with some clouds. Ridgetop winds light from the NW. Alpine temperatures near -7 and freezing levels at 1200 m. Friday: The ridge will remain over the region with mainly dry, sunny conditions. Ridgetop winds light from the NW. Alpine temperatures near -7 and freezing levels at 1300 m.

Avalanche Summary

On Monday, natural slab avalanche activity occurred up to size 2 on N-E aspects and above 2000 m. Numerous natural loose dry avalanches also occurred up to size 1.0 from steeper terrain features.

Snowpack Summary

In much of the region, up to 80 cm recent snow overlies older interfaces comprising of surface hoar and sun crusts. The storm slab above these interfaces has the potential for wide propagations and surprisingly large avalanches.Wind slabs and new cornice development exist at ridgelines and on lee slopes. These are likely sensitive to human triggers. A strong melt-freeze crust exists at 1700 m and below and is generally bridging any deeper instabilities. The average treeline snow depths sit near 250 cm.

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.