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Avalanche Forecast

Archived

Feb 27th, 2016–Feb 28th, 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.

Small wind slaps in steep or exposed terrain could have severe consequence.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Unsettled weather on Sunday with flurries amounting to 5-10cm. Ridgetop winds spike Sunday afternoon with strong southwesterlies, then die down for remainder of period. Freezing levels should remain under 1600m.

Avalanche Summary

On Friday numerous natural loose wet avalanches to size 2 were reported on steep solar aspects in the alpine.

Snowpack Summary

Sunday's snow will bury the widespread surface hoar being reported up to 20mm in size on shady aspects at all elevations throughout the region. The strong winds associated with Sunday's storm will build fresh wind slabs on lee features in alpine. Cornices are large and looming. The mid February layer is down 70-100cm and is the primary layer of concern. This layer is a crust and generally well bonded to the overlying persistent slab. However, in isolated areas on northerly aspects between 1800-2100m the layer is surface hoar which means there are still a few "land mines" out there that if triggered could produce large destructive 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.

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.

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.