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Avalanche Forecast

Archived

Apr 20th, 2015–Apr 21st, 2015

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

Regions

Glacier.

We're in a typical spring pattern with some overnight crust recovery and high daytime temperatures. Watch for the rapid deterioration of the upper snowpack on solar aspects. Plan to stay off of these slopes by mid to late morning.

Weather Forecast

Another clear sunny day is upon us with few clouds and little wind. Freezing levels are steadily rising to 2700m and expected to reach 3000m tomorrow with no overnight refreeze tonight. High pressure ridge is slowly breaking down and by Wednesday we'll have some cloud cover and light rain at most elevations into Thursday.

Snowpack Summary

Overnight refreeze created a surface crust over moist or wet snow. The snowpack on solar aspects is mostly moist and composed of multiple crusts. This will differ on sheltered north aspects in the alpine where dry snow can still be found above 1900m. Weak layers still exist in the upper snowpack on crusts or surface hoar on north aspects higher up.

Avalanche Summary

Yesterday, natural slab avalanche on Mt Fidelity peak, size 2.5, south aspect, 2500m, down ~30cm, ~200m wide, ~150m long. Similar avalanche on Bruins Ridge, 2 days ago, size 2.5, E aspect, 100m wide, 30cm deep, 250m long which ran into Hospital Bowl. Several solar avalanches to size 2.5 and one size 3 glide crack release in the highway corridor .

Confidence

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.