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Avalanche Forecast

Archived

Dec 27th, 2013–Dec 28th, 2013

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

Regions

Cariboos.

Confidence

Fair - Due to the number of field observations

Weather Forecast

Saturday: Mainly cloudy with a chance of flurries and possible sunny breaks. The freezing level drops to valley bottom and winds are light to moderate from the northwest. Sunday: Mainly cloudy with a chance of flurries or light snow – around 5 cm. The freezing level is near valley bottom and winds are moderate gusting strong from the W-NW. Monday: Flurries or periods of snow. The freezing level should remain at valley bottom.

Avalanche Summary

Reports from the past couple days are very limited. It's likely that the combination of new snow, wind, and mild temperatures kicked off a natural avalanche cycle in some areas over the past couple days. The additional load may have also been enough to trigger deep persistent weaknesses in isolated areas. Cooler temperatures and drier conditions on the weekend should help to stabilize the snowpack, but rider triggering will certainly remain a concern. Watch for steep slopes that did not previously avalanche, wind loaded areas, and high north-facing terrain with variable snow cover.

Snowpack Summary

An additional 20-30 cm of snow has fallen accompanied by moderate to strong W-SW winds and mild temperatures. New dense wind slabs are likely in exposed lee terrain at and above treeline. Up to 80cm of snow now sits on a variety of weaknesses from early December (surface hoar, faceted snow, and/or a crust). An older layer of surface hoar or facets from late November can be found deeper in the snowpack. Recent snowpack tests results vary but some are showing this layer "pop" with medium loads, indicating a potential for human triggering.Snowpack depths vary, but in general up to 150 cm of snow can be found at treeline, with 100-200 cm in the alpine. In many places we're still dealing with a relatively thin snowpack (thanks to a windy early season) so there's not a whole lot of snow between riders and the sugary snow (facets) near the ground. The basal facet/crust combo has been recently active in parts of the region.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.