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Avalanche Forecast

Archived

Mar 18th, 2016–Mar 19th, 2016

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

Regions

Little Yoho.

Simplify your terrain choices this weekend. Sunny skies Saturday will increase the danger on solar aspects and weaken cornices on lee aspects. SH

Weather Forecast

A good freeze overnight into Saturday with mainly sunny skies. Freezing levels will shoot to 2000m quickly with high solar input and a temperature inversion (warmer air aloft). Sunday may be even warmer. Light Westerly winds through the weekend.

Snowpack Summary

40-60cm of recent, dry storm snow overlies a well settled mid and lower pack. Observations are limited but we suspect there are buried sun crusts on steep E through W aspects with 60-100cm above (similar to Banff region).  Isolated thin snowpack areas have weaker facet layers, but this is not a widespread snowpack characteristic of the region.

Avalanche Summary

Avalanche control on Mts. Stephen and Dennis Friday produced avalanches to size 3, one of which slid to ground in a steep, thin snowpack area. That flight saw numerous slides to size 3 mainly along and East of the divide where the basal weak layers are more prevalent.  These were on N- NE aspects in the alpine in the last 24-48 hours.

Confidence

Freezing levels are uncertain on Saturday

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.