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Avalanche Forecast

Archived

Jan 17th, 2013–Jan 18th, 2013

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

Regions

South Columbia.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Friday: Moderate to strong NW winds. Alpine temperature near -2. No snow.Saturday: Moderate to strong W winds. Alpine temperature near -2. No snow.Sunday: Light to moderate W winds. Alpine temperature near -2. No snow.

Avalanche Summary

A natural and human-triggered cycle of wind slabs to size 2 was observed on Tuesday. Solar-triggered loose snow avalanches also failed on steep sun-exposed slopes. Occasional skier-triggered avalanches have been failing on persistent weak layers from early January over the last week. These have mostly been on steep south-facing slopes or sheltered slopes below treeline.

Snowpack Summary

Strong NW through SW winds have left wind slabs in many areas, even at treeline. Around 40-60 cm settled snow sits above surface hoar (found especially at and below treeline in sheltered areas), a sun crust (on steep S to SW -facing slopes) and facets. The distribution of these weaknesses is patchy, but where they exist, it may still be possible to trigger a large avalanche with the weight of a person or snowmobile. Test results on these interfaces vary from no result to moderate, sudden results. A strong mid-pack overlies a weak facet/crust layer near the base of the snowpack, which is now considered inactive.

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.