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Avalanche Forecast

Archived

Feb 13th, 2018–Feb 14th, 2018

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

Regions

South Coast.

Touchy new storm slabs are expected to form over Tuesday night. Wind affected areas where new snow will fall on firm crust are the most concerning.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Tuesday night: Periods of snow bringing approximately 20 cm of new snow. Moderate to strong southwest winds.Wednesday: A mix of sun and cloud with clearing over the day. Light to moderate northeast winds. Freezing level rising to 900 metres with alpine high temperatures of -3.Thursday: Mainly cloudy with cloud and light flurries increasing over the day. About 5 cm of new snow accumulating by Friday morning. Light southwest winds, increasing overnight. Freezing level to 500 metres with alpine high temperatures of -4.Friday: A mix of sun and cloud. Light to moderate northwest winds. Freezing level to 900 metres with alpine high temperatures around -2.

Avalanche Summary

On Saturday, a cornice collapse was the likely cause of a size 2 avalanche on a north facing slope near the West Lion. See here for images and more details. Looking forward, avalanche danger will increasing quickly over Tuesday night as new storm slabs form over the firm crust that exists at most elevations. This crust is likely to act as a very effective sliding layer that will resist bonding to the new snow over the near term. Treeline elevations may see the touchiest conditions develop because of the combination of this crust with the added factor of winds promoting slab formation.

Snowpack Summary

Increasing flurries are expected to bring about 20 cm of new snow to the region by Wednesday morning. Beneath the new snow, the upper snowpack at most elevations has locked up as a firm rain crust. In the high alpine, the new snow is accumulating over wind affected surfaces and thin wind slabs. It will take time for the new snow to form a solid bond with these varied surfaces - especially the rain crust. The average snowpack depth at treeline is 300 cm of well settled snow with no significant layers of concern.

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.

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.