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Avalanche Forecast

Archived

Mar 18th, 2012–Mar 19th, 2012

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

Regions

Northwest Coastal.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Monday: A mix of sun and cloud with a slight chance of flurries in some areas. The freezing level should be at valley bottom overnight, rising to 500-600m during the day. Winds are light, rising to moderate from the SE in the afternoon. Tuesday and Wednesday: Light to moderate snow - 10-15cm each day. The freezing level is around 500m and winds are moderate to strong from the S-SW.

Avalanche Summary

Some areas saw a fairly widespread cycle on southerly aspects on Friday and Saturday with avalanches up to Size 3. Other reports indicate primarily moist loose snow avalanches up to Size 2 on steep south aspects on Saturday. There are also reports of natural avalanches up to Size 3 on northerly aspects in the Bear Pass area.

Snowpack Summary

Sporadic strong and variable winds have redistributed moderate amounts of recent storm snow into wind slabs that most commonly exist in the lee of terrain features at treeline and in the alpine. The mid-pack varies greatly depending on location. You may find up to three persistent weak layers. First, a surface hoar layer buried mid-March, now buried 60-80cm deep, which seems to be most prevalent in the mountains around Stewart. Second, a surface hoar layer buried early March, buried around 1m deep, has been causing problems north of Terrace. Third, a weak layer comprising surface hoar or facets, buried early in February, is now more than 1m down. This has been causing issues particularly in the north around Ninginsaw. However, recent reports indicate this layer is becoming difficult to trigger. Bear in mind that triggering any of these persistent weak layers would likely result in a very large avalanche. Cornices in the region are reported to be very large and potentially unstable.

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.

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.