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Avalanche Forecast

Archived

Mar 28th, 2013–Mar 29th, 2013

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

Regions

Northwest Coastal.

Large natural and human-triggered avalanches have occurred on a persistent weakness buried on March 9th. Continued reactivity is expected on this layer throughout the weekend.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

No precipitation is expected for the forecast period. Mainly clear skies are forecast for Friday and Sunday, although high cloud is expected on Saturday.Winds will be light from the west on Friday switching to light and northwesterly on Saturday and Sunday.Freezing levels will climb steadily from 1200m on Friday to about 2400m on Sunday.

Avalanche Summary

Natural slab avalanches up to 2.5 have been reported, likely failing on the March 9th layer. Loose wet sluffs up to 2.0 have also been reported. As well, a recent size 2.5 slab avalanche was remotely triggered by a skier in the Hidden Lake area near Shames. Once again, the March 9 surface hoar layer was the culprit. Nobody was caught in the slide.

Snowpack Summary

Recent snow has settled with the influence of warm temperatures and surface hoar is growing on shaded slopes. Solar aspects and lower elevation terrain are now well into a daily melt-freeze cycle. Wind slabs may be found at alpine and treeline elevations on many aspects due to variable winds. Between 50-75cm below the surface is layer of surface hoar buried on March 9th which is variably reactive. In some areas it is stubborn and requires a significant trigger, while in other areas the layer is well preserved and primed for human triggering with the potential for very large avalanches. Check out the Forecaster's Blog for related discussion. The mid snowpack is generally well settled and strong. Cornices are large and untrustworthy, especially when the sun is out.

Problems

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.

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.