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Avalanche Forecast

Archived

Mar 22nd, 2012–Mar 23rd, 2012

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

Regions

South Coast.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Mainly sunny and mild weather is expected through the weekend. The freezing level should be near valley bottom overnight and rise to 1200m Friday and 1500m on Saturday and Sunday. Ridge top winds are generally light from the south.

Avalanche Summary

Wednesday was a very active day in the Coquihalla Pass. Explosive control produced several Size 4 avalanches running full path and taking out extensive mature timber, and numerous Size 2-3 avalanches. A few large natural avalanches were also observed in lee terrain. Explosive control on the Duffy Lake road on Wednesday results in one Size 2.5 slab avalanche on a SW aspect and many large black holes with no result.

Snowpack Summary

Solar aspects will likely go through a melt-freeze cycle with a frozen surface overnight becoming moist throughout the day. Snowfall amounts over the past few days have varied significantly throughout the region with southeast areas (Coquihalla) receiving up to 60cm of new snow, while places like the Duffy Lake have seen considerably less. Expect wind slabs to be deep in heavy snowfall areas and thin in other areas. Crusts down around 60cm can be found on solar aspects in the Duffey Lake, Chilcotin, and down closer to 1m in the Coquihalla. These exhibit moderate to hard, sudden results in snowpack tests. Deeper persistent weak layers are variable in distribution across the region. A crust/surface hoar/facet layer buried in early February, now down about 1.5m, is still is a key concern. It is especially prevalent on south-facing slopes above treeline, and all slopes below treeline. Although the likelihood of triggering this layer has decreased, the potential for surprisingly large avalanches remains. Cornices are reported to be very large and should be given a wide berth.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.