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Avalanche Forecast

Archived

Dec 29th, 2018–Dec 30th, 2018

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

Regions

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Winds will continue to transport fresh snow onto lee slopes through much of Sunday. Stay off of steep wind loaded terrain where deeper slabs will build. Enjoy the fresh snow in wind sheltered spots, watching for storm slabs on specific terrain features like convex rolls or steep unsupported slopes.

Discussion

Snowpack and Avalanche Discussion

It's worth calling out that we have a relevant professional snowpack observation from 12/28 in the West Central zone, from north of Darrington on Green Mountain. The snowdepth jumps dramatically above 4500', with marginal cover below 4000'.  A generally strong and deep snowpack was found above 5000'. The 12/9 buried surface hoar/facet layer was identified but gaining strength.

Snowpack Discussion

Updated Regional Synopsis coming Sunday 12/30

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.