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Avalanche Forecast

Archived

May 8th, 2019–May 9th, 2019

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

Regions

Jasper.

Soaring freezing levels and hot sun will stress a relatively cool, wintery snowpack.  The sound of natural avalanches will echo around the hills this weekend - steer clear of avalanche terrain Friday onwards. Start very early if traveling on snow.

Weather Forecast

Freezing level soaring, with valley bottom highs forecast in the 20's.  Generally scattered cloud, warm overnight temperatures.

Thursday: Mainly sunny, Treeline low -1, high 6 °C, Light NW winds, Freezing level 3100 metres.

Friday: Treeline low 2.5, High 7. freezing level 3000m.

Saturday: Treeline Low 5, High 1, freezing level 3500m1

Snowpack Summary

Surface layers becoming wet daily, as the snowpack is forced to transition rapidly from Winter to Spring.  Snow from frequent small Spring storms has settled quickly, but overlies crusts and facets in the upper snowpack. The crusts are thick on solar aspects.  The snowpack remains faceted on shady aspects, and weak in shallow areas.

Avalanche Summary

On Wednesday, numerous small (size 1-1.5) loose wet avalanches were observed on N and E aspects near Jasper townsite.  On Sunday, a large (size 2.5) natural slab avalanche was observed at 2400m on a NE aspect of Pyramid Mountain. 

Confidence

Due to the number of field observations

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.

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.

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.