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Avalanche Forecast

Archived

Dec 15th, 2015–Dec 16th, 2015

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

Regions

Northwest Coastal.

You don't have to be an avalanche expert to submit to the MIN. If you've been out in the mountains, we'd love to hear about what you've seen.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Mainly clear skies are forecast for Wednesday and Thursday morning. Increased cloud is expected throughout the day on Thursday with 5-15cm of new snow falling between Thursday afternoon and Friday morning. Ridgetop winds should be light to moderate from the north on Wednesday, switching to strong and southwesterly with Thursday's snowfall. Freezing levels should hover around valley bottom for the forecast period. For a more detailed weather overview, check-out our Mountain Weather Forecast at: avalanche.ca/weather

Avalanche Summary

At the time of publishing this bulletin, there were no new reports of avalanche activity. I'm sure there was a round of new wind slab activity on Tuesday in response to new snow and strong winds. New wind slabs may remain sensitive to human triggering for longer than normal due to the presence of underlying surface hoar.

Snowpack Summary

On Monday night, between 18cm (in the north) and 26cm (in the south) of new snow and strong variable winds formed new wind slabs at treeline and in the alpine. Below the new snow, you may find a layer of surface hoar. I'd keep an eye on this layer as the overlying slab gets deeper and gains cohesion. Up to a meter below the surface you may find another layer of buried surface hoar. In some areas, this layer may be sensitive to human triggering and wide propagations while in other areas it is non-existent or has gained significant strength. Due to the variable nature of this weak layer, I'd dig down to test for it before committing to any steep lines on slopes at or below treeline.

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.