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Avalanche Forecast

Archived

Mar 21st, 2017–Mar 22nd, 2017

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

Regions

Little Yoho.

Large explosive triggered avalanche occurred today. The potential for very large human triggered avalanches on the weak facets remains high. Avoid exposure to overhead hazard and stick to moderate angled supported terrain to enjoy the new snow.

Weather Forecast

Expect flurries with warmer temperatures and freezing levels around 1900m will for Wednesday before a cooling trend on Thursday. Alpine temperatures should remain below freezing. Winds will be moderate out of the SW.

Snowpack Summary

40 to 80 cm of storm snow with SW winds in the last two weeks has helped create a thick supportive slab over the weak basal facet layer in thin snowpack areas. Rain on Saturday created a surface rain crust to about 2000m which is now frozen and covered by new snow. The valley bottom snowpack is also refrozen after becoming rain saturated.

Avalanche Summary

Natural activity to size 3+ was observed Monday in Yoho and Banff. Both natural and explosive control work today and over the past several days has produced massive results in the Lake Louise and Yoho regions with impressive propagation. Many large avalanches have run to the bottom of their run outs entraining moist snow at lower elevations.

Confidence

Due to the number and quality of field observations

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.

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.