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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 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.

Regions

South Columbia.

Confidence

Good - -1

Weather Forecast

A small "Pineapple" (or maybe we should refer to it as a Papaya due to lack of moisture in the Interior) is pushing through the Southern ranges. Tuesday night snow amounts up to 10cms. Wind 60-90km/hr from the SW. Light precipitation during the day. Freezing levels rising to 2000m through the day. Wednesday night snow amounts 10-20cms with 20cms more realistic in the Northern parts of the region, less in the South. Freezing levels fall to 1000m. Thursday: Snow amounts near 10cms. Freezing levels falling from 1000m to valley bottom by Thursday afternoon. Friday: to 600m by early afternoon. Friday: Mix of sun and cloud. Light snow amounts. Light winds from the SE. Freezing levels valley bottom.

Avalanche Summary

In the Selkirks continued avalanche activity is being reported. Many of the recent avalanches have occurred due to large triggers (cornice fall, explosive testing). Yesterday there was a size 2 sled triggered avalanche that occurred west of Revelstoke on a South aspect near 1800m. No injuries reported. The mid-December persistent weak layer is buried down 80-120cms and is still a layer of concern. Avalanches that are failing on this layer are large-very large (sz 2-3.5). As the natural activity has somewhat tapered off, the sensitivity to skier, or sledder triggers are likely. Remote triggering (setting off avalanches from afar, with wide fractures) continues to be reported. I would also be suspicious of low angle terrain in the trees. It seems to be catching people by surprise.

Snowpack Summary

New snow up to 10cms has fallen over the region. This blankets all elevations and buries a new surface hoar layer that formed over the New Year. Reports indicate that the SH crystals range in size up to 10mm. The previous storm snow that fell over Christmas has been blown around by steady SW winds and has formed wind slabs. Wind slabs are widespread and found in exposed alpine and treeline locations. Below the surface 80-120cms lurks a surface hoar/facet/crust interface (persistent weak layer) from mid-December. Testing on this layer has shown moderate to hard results with sudden planer characteristics. This weak layer has been very reactive; producing large, destructive avalanches. It still remains a layer of concern and should continue to be on your radar. Below this layer sits a strong mid pack.

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.