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Avalanche Forecast

Archived

Apr 14th, 2017–Apr 15th, 2017

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

Regions

Little Yoho.

West winds have created touchy new windslabs. There is the potential for more snow Saturday. This, coupled with increasing winds will raise the hazard this weekend.

Weather Forecast

West winds will continue to build late Friday reaching strong values midday Saturday before diminishing Sunday. Up to 15cm of precip is in the forecast for the 93N with less further South for Saturday. Freezing levels look to stay around 1500m for Saturday but will creep higher Sunday and higher still Monday with increasing solar influence.

Snowpack Summary

Small amounts of snow over this past week have added up to about 20-40cm that moderate west winds redistributed Thursday night. A new crust formed to 2300m on North aspects late Thursday and much higher on sunny slopes. At treeline and above, the midpack is a 120cm+ firm slab with few weaknesses overlying weaker basal facets in much of the region.

Avalanche Summary

Late day heating Thursday may have triggered two sz 2.5 storm slabs near the Lake Louise resort 60cm x 100m wide. West winds overnight resulted in several skier triggered windslabs propagating up to 100m wide in the alpine. Skiers deliberately triggered a sz 2 windslab at the top of the North gulley on Mt Cathedral.

Confidence

Intensity of incoming weather systems is uncertain on Saturday

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.

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.

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.