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Avalanche Forecast

Archived

Apr 7th, 2021–Apr 8th, 2021

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

Regions

Little Yoho.

There is a huge range of conditions over the forecast region. Also, some unexpected deeper releases two days ago have lowered our confidence. Winds should decrease tomorrow, but watch for fresh wind slabs in the alpine.

Weather Forecast

5-10cm are expected along the divide and West tonight. Strong SW winds will diminish Wednesday night and will be moderate for Thursday. Temperatures will dip below freezing tonight at valley bottom, and 3000m temperatures will drop to -15C.

Snowpack Summary

The snow surface is mix of crusts to 1800 m, and dry powder snow on north facing slopes above 1800 m. New snow, strong winds and cooling temps have promoted some wind slab development. Treeline and below treeline elevations should become frozen and stay mostly frozen. Quite a variable spring snowpack.

Avalanche Summary

No new avalanches reported today. There were a few deeper releases yesterday on Mt. Des Poilus and in the Lake Louise backcountry up to size 3.5. It is unsure the sliding surface, but they started as smaller slabs that had enough weight to dig down deeper. Also yesterday an almost full burial near Lake Agnes in the alpine with no injuries.

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Problems

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.

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.