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Avalanche Forecast

Archived

Dec 21st, 2015–Dec 22nd, 2015

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

Regions

South Columbia.

The wind effect from the last storm seems to be highly variable. The best (and safest) riding may be found on sheltered slopes at treeline and below.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

A fairly benign weather pattern is setting up for the forecast period. Light flurries are expected for Tuesday, but snowfall amounts shouldn't exceed 5cm. Isolated flurries with occasional sunny breaks are forecast for Wednesday and Thursday. Ridgetop winds are forecast to remain mainly light for all 3 days while alpine temperatures should hover between -12 and -15.

Avalanche Summary

On Sunday, we received a few reports of widespread natural and human-triggered wind slab avalanche activity to size 2. As the weather eases, so should natural wind slab avalanche activity. That said, human triggering will remain a concern for a few days.

Snowpack Summary

Throughout the weekend there was up to about 70cm of new snow in the Monashees and slightly less in the Selkirks. Strong to extreme southerly winds have redistributed much of this snow into deeper wind slabs in exposed lee features in the alpine and at treeline. In more sheltered terrain, I would expect deep powder and really good riding. Between 80 and 150cm below the surface you'll likely find a weak layer of well-developed surface hoar. This layer is most widespread and reactive at lower elevations (between 1400m and 1800m.) Snow pit tests suggest that human triggering of this interface has become unlikely. That said, if it does fail the overlying slab is stiff enough to propagate over a wide distance. Below this layer, the snowpack is thought to be generally strong and well-settled.

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.