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Avalanche Forecast

Archived

Mar 22nd, 2016–Mar 23rd, 2016

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.

Give cornices a wide berth.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

A frontal system is expected to bring around 10-15 cm snow on Wednesday night, with moderate to strong SW winds and the freezing level around 1400 m.  Snow showers linger on Thursday before a ridge brings clearing skies on Friday.

Avalanche Summary

A few small storm slabs were triggered by explosives and a skier yesterday.

Snowpack Summary

Surface snow layers are becoming moist and weak in the heat of the day, but generally settling and bonding with warm temperatures and sunshine. Several crusts are buried in the upper snowpack. Some of these are breaking down on sunny aspects. The late February persistent weak layer down 70 to 120 cm remains a lingering concern. Test results are variable, with occasional sudden planar (pop) results. This interface may remain more reactive on northerly (shaded) aspects above about 1700 m, where buried surface hoar has the best chance of preservation. On sunny aspects, this interface may be a crust/ facet layer. It is most likely to be triggered by a cornice fall or from a thin snowpack area.

Problems

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.