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Avalanche Forecast

Archived

Apr 19th, 2021–Apr 20th, 2021

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

Banff Yoho Kootenay.

Tuesday and Wednesday look like beautiful days to be in the mountains. Start and finish your trips early to take advantage of the good overnight freezes.

Weather Forecast

Tuesday and Wednesday look like beautiful days to be in the mountains. Sunny with light winds and good overnight freezes. Freezing levels will rise to around 2200m both days but the sun is strong this time of year so expect solar aspects to feel warmer than that. Thursday is looking to be cool with light snow.

Snowpack Summary

10-20 cm of new snow on Sunday refreshed the ski quality. This sits on crusts to ridgetop on solar aspects and below 2000m on shaded aspects. Persistent layers in the mid and lower snowpack were re-activated in a few instances during the heating last week producing large avalanches with large loads (cornice failures and explosives). 

Avalanche Summary

An avalanche cycle to size 3 occurred with last weeks warm up. Primarily loose wet and cornice triggered avalanches with the occasional larger avalanche failing on persistent layers in the mid and lower pack. Since the temperatures cooled on Sunday, no new avalanche activity observed.

Confidence

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.