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Avalanche Forecast

Archived

Apr 15th, 2017–Apr 16th, 2017

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.

Travel and ski conditions should improve for Sunday and Monday but watch for newly formed wind slabs and cornices, as well as the effects of daytime heating as the skies clear.

Weather Forecast

Moderate to strong west winds with light snowfall will continue through Saturday night before easing up on Sunday morning. Freezing levels will creep higher Sunday and higher still Monday with increasing solar influence as a ridge and clearing skies arrives on Sunday afternoon.

Snowpack Summary

5cm of new snow over a melt freeze crust on all aspects at tree line, and up to 2900m on solar aspects. 20-50cm of snow over the last week in the alpine. Moderate west winds creating soft slabs and rapid cornice growth. At tree line and above the mid-pack is a 120cm+ firm slab with few weaknesses. Thin snow pack areas may have weaker basal facets.

Avalanche Summary

Reports of a couple skier triggered wind slabs in the alpine at Bow Summit and Cathedral Peak on Friday as the winds increased. Propagation up to 100m was reported. On Saturday local ski areas were seeing rapid cornice growth and were able to ski cut small wind slabs in lee areas throughout the day. No new naturals observed but visibility was poor.

Confidence

Timing of incoming weather systems is uncertain on Monday

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.

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.