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Avalanche Forecast

Archived

Apr 19th, 2017–Apr 20th, 2017

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

Regions

Little Yoho.

Isolated windslabs exist at ridgetop on north and east aspects in the alpine but are generally small and predictable. Start and finish your trips early before the strong April sun destabilizes the snowpack.

Weather Forecast

Thursday looks to be partly cloudy with some afternoon flurries and freezing levels rising to ~ 2400m. Friday morning there will be a weak freeze, but sunny skies will make afternoon temperatures even warmer. Saturday looks to be the warmest day as we start to finally get into a springlike pattern. Winds look to be light through the period.

Snowpack Summary

The snowpack is a real mixed bag right now: totally dependent on aspect and elevation. At treeline and above, melt freeze crusts exist to ridgetop on solar aspects, while on north aspects, dry surface snow still exists above ~2200m. Below treeline the snowpack becomes wet through the day. The snowpack is slowly transitioning to a spring snowpack.

Avalanche Summary

Two size 3's were reported in the Sunshine Village backcountry. These were both initiated by cornice failures in the alpine at ~2800m which triggered the deep persistent weak layer and failed on the ground.

Confidence

Timing or intensity of solar radiation is uncertain

Problems

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.

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.