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Avalanche Forecast

Archived

Jan 3rd, 2012–Jan 4th, 2012

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

Regions

South Rockies.

Confidence

Good - -1

Weather Forecast

Wednesday: Mix of sun and cloud. Light precipitator today up to 5mm. Ridgetop winds from the SW 70-100km/hr. Freezing levels rising to 2000m throughout the day. Thursday: Snow amounts up to 5cms in the morning. Ridgetop winds from the West 55-70km/hr. Freezing levels falling back to valley bottom midday. Friday: Mix of sun and cloud. Freezing levels remain near valley bottom. Ridgetop winds light-moderate from the SW.

Avalanche Summary

On Monday a skier triggered a size 2 slab avalanche in the Harvey Pass area. A wind slab from the ridgecrest was triggered, then stepped down 55cms to a weak surface hoar/ facet layer beneath the surface. Please visit our incident report database on our website for more details @ avalanche.ca.

Snowpack Summary

The CAC Field team headed to Harvey Pass on Tuesday and completed a fracture line profile on yesterday's skier triggered avalanche. The total HS (height of snow) in that area is 180cms. A stiff wind slab was triggered and stepped down 55cms to the mid-December surface hoar/facet layer. Compression tests done showed hard results, but sudden planar characteristics. I suspect you can find this buried layer to the West of the divide in most locations. As soon as you travel to the east surface hoar is spotty, and/or non-existent. The snowpack to the east is 100-120cms in depth, and widespread wind slabs have formed lee to the SW in upper elevations. Many windward areas are scoured. The mid pack is generally well consolidated. At the bottom of the snowpack 20cms of 4F facets and depth hoar exist.

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.