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Avalanche Forecast

Archived

Apr 16th, 2017–Apr 17th, 2017

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

Regions

Little Yoho.

Wind and storm slabs in the alpine continue to react to skier traffic today.

Weather Forecast

Clear skies will lead to a solid freeze overnight Sunday. Despite the potential for flurries Monday, freezing levels are still forecast to reach 2200m as unsettled air tracks east from the coast: don't rule out loose wet activity and light rain BTL. Tuesday should see West winds return to the moderate range with the potential for flurries.

Snowpack Summary

Sunday morning saw 5 to 10cm storm snow over recent crusts below 2300m. Solar heating is making new crusts today. 20-50cm of snow over the last week in the alpine sits over crusts on S aspects and was redistributed by moderate west winds. At tree line and above the mid-pack is a 120cm+ firm slab overlying weaker basal facets in much of the region.

Avalanche Summary

Skiers triggered a sz 2 slab at 2500m on the S aspect of Mt Jimmy Simpson 40 deep over a crust on a 30 degree slope. A field team on the Wapta reported sz 2 windslabs: 1 on the SE aspect of Mt Ayesha, and 2 on the East aspect of Arete Peak, an icefall triggered sz 2 slab off of the East aspect of Mt. Collie, and sz 1.5 loose wet off the S of Gordon

Confidence

Freezing levels are 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.