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Avalanche Forecast

Archived

Dec 15th, 2017–Dec 16th, 2017

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

Regions

Northwest Coastal.

Saturday is storm day! Avoid avalanche terrain during periods of heavy loading from rain, new snow and wind.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Saturday: Snow amounts 20-30 cm. Alpine temperatures -2 and freezing levels 800 m. Ridgetop winds strong from the southwest.Sunday: Cloudy with sunny periods and new snow amounts 3-10 cm. Alpine temperatures -3 and freezing levels 600 m. Ridgetop winds light with strong gusts from the southwest.Monday: Cloudy with isolated flurries. Alpine temperatures -3 and freezing levels 600 m. Ridgetop winds light from the southwest.Check out the Mountain Weather Forecast for more detail.

Avalanche Summary

On Friday, wet slab avalanches size 1-2 were reported from steep terrain where the ground cover consists of smooth rock slab features. These avalanches went to ground. Widespread natural avalanche activity expected through the forecast period with new rain, snow and wind.

Snowpack Summary

Up to 30 mm of precipitation fell as a rain and saturated the snowpack up to 800 m on Thursday. On Friday, the freezing levels dropped and the new snow is currently building storm slabs on all aspects and elevations. Below the surface sits a well-settled snowpack overlying several layers of interest. Down 70-100 cm you'll likely find a 5-10 cm thick crust which was buried on November 23 and in some areas, a feathery surface hoar layer down 50-60 cm producing moderate snowpack test results. The widespread crust/facet interface that was buried at the end of October can now be found 100-200 cm deep and exists region wide.

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.

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.