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Avalanche Forecast

Archived

Feb 3rd, 2012–Feb 4th, 2012

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

Regions

Kootenay Boundary.

Confidence

Fair - Freezing levels are uncertain on Saturday

Weather Forecast

High pressure is expected to continue to dominate the interior until the middle of next week. Warm air that is trapped above about 2100 metres continues to cause above freezing temperatures, sunny skies, and valley cloud. Valley temperatures are expected to drop below freezing overnight. The inversion may continue until Sunday. If the valley cloud clears, then we should get a good freeze in the alpine.

Avalanche Summary

Explosive control in the Kaslo to New Denver highway corridor on Thursday produced several size 2.5 moist releases that pushed storm snow to the middle of the runout of 2 km long paths. These slides started between 2000 and 2300 metres on S-SW aspects. A larger explosive controlled avalanche occurred at Bear Lake from a SE aspect in the alpine. The avalanche was size 3.5 dry slab with an average crown of 160 cm and ran full path, 1100 vertical metres for 2.5 km. Reports of loose dry sloughing in steep terrain from several operators in the area up to size 1.5. Explosive control at Kootenay Pass produced several avalanches size 2.5-3.0 on cross loaded slopes with crowns between 50-100 cm.

Snowpack Summary

New sun crusts are developing on steep solar aspects. Warm air trapped in the alpine caused temperatures to remain above freezing on Thursday night above about 2100 metres. Pin-wheeling and other signs of moist snow have been observed on solar aspects at and above treeline. Continued warm temperatures in the alpine may trigger buried weak layers on solar aspects. Steep planar slopes with shallow snowpacks are the most suspect. The recent storm snow layer is about 30-50 cm thick and is quite variable across the region. There are a couple of thin crusts buried below the storm snow that have been producing moderate to hard shears in tests. Some areas are still getting sudden planar shears on the mid-december surface hoar layer.

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.

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.