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Avalanche Forecast

Archived

Dec 22nd, 2015–Dec 23rd, 2015

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

Regions

Cariboos.

Low Danger does not mean No Danger. Make observations continually as you travel.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

A benign yet cool weather pattern has set up and will continue for the forecast period. For each day, expect a mix of sun and cloud with isolated flurries. Ridgetop winds are expected to remain light while alpine temperatures should remain between -12 and -16.

Avalanche Summary

Evidence of a fairly widespread cycle of soft wind slab avalanches in the size 1-1.5 range was observed in extreme terrain on Monday. The avalanches occurred in response to new snow and wind over the weekend.

Snowpack Summary

20-40cm of low-density snow overlies soft wind slabs which formed last weekend. The few observations we've had suggest a good bond within the storm layers in the upper snowpack. I'd still remain cautious in upper elevation lee terrain where buried wind slabs may still be sensitive to human triggering. Between 80 and 130cm below the surface you'll likely find a weak layer of well-developed surface hoar which was buried in early December. This layer is most widespread and reactive at lower elevations (between 1100m and 1800m.) Snow pit tests suggest that human triggering of this interface has become less likely. 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.