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Avalanche Forecast

Archived

Dec 23rd, 2018–Dec 24th, 2018

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

Regions

South Columbia.

The persistent slab problem is best managed with patience and conservative terrain choices. Read more in the new forecaster blog here.

Confidence

High - Due to the number and quality of field observations.

Weather Forecast

SUNDAY NIGHT: Isolated flurries with localized accumulations of 2-5 cm, light wind from the southwest, alpine temperatures drop to -8°c. MONDAY: Mostly cloudy with a few sunny breaks, light wind, alpine high temperatures around -8°c. TUESDAY: Mix of sun and cloud, light wind, alpine high temperatures around -10°c. WEDNESDAY: Mostly cloudy, light wind, alpine high temperatures around -10°c.

Avalanche Summary

Preliminary reports from Sunday indicate the most recent 20 cm of new snow was reactive to skiers on steep and convex features. No significant avalanche activity was reported on Saturday, as natural and human triggered activity has started to tapered off. However, as recent as Friday, large (size 2-3) persistent slab avalanches were occurring naturally. There have also been a few notable persistent slab avalanches remotely triggered from skiers on adjacent slopes. Most recently, a few large (size 2-2.5) avalanches on north-facing slopes at treeline elevations were remotely triggered by skiers in the Selkirks on Wednesday.

Snowpack Summary

Recent wind from the southwest has formed wind slabs in the alpine and around treeline. A week of stormy weather has deposited 50-100 cm of snow above a weak layer of facets (sugary snow), surface hoar (feathery crystals), and a sun crust (on south aspects) that formed during the dry spell in early December. This layer has been responsible for large persistent slab avalanches over the past week, particularly on northeast facing slopes above 1900 m and on south-facing slopes in the alpine. The potential exists for smaller avalanches to step down and trigger this layer, resulting in very large avalanches. Another weak layer from mid-November is now buried up to 120 cm, but has been less active recently. At the base of the snowpack is a crust that formed in late October.

Problems

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.

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.