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Avalanche Forecast

Archived

Dec 27th, 2015–Dec 28th, 2015

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
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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New wind slab should be found on a variety of aspects Monday, mainly near and above treeline. Remember MODERATE danger means human triggered avalanches are possible. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees. 

Detailed Forecast

Wind slab will most likely be found on north to southeast aspects near and above tree line, except locally on west-northwest aspects near the Cascade Passes. NW winds will redistribute new snowfall to lee SE slopes above treeline Monday. Wind and storm slab avalanches should stay within recent storm layers. Test for inverted strong over weak storm snow and give cornices a wide margin.

Beware of loose dry avalanches in steep non-wind affected terrain that could have unintended consequences such as knocking you off your feet and into a terrain trap.

There have been snow immersion fatalities in tree wells already this season at Snoqualmie and in Canada. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees and maintain visual contact.  

Snowpack Discussion

For the week ending on Dec. 24th, a snowy and cool storm cycle brought 5-9 feet of snowfall along the west slopes. Only light additional accumulations over the last few days have allowed the snowpack to gradually settle, but it remains deep out there with generally great skiing and riding!  

The upper snowpack should generally be right side up with increasing hardness with depth. Moderate S-SW transport winds with Sunday's system may have built new wind slab on N through E aspects. However, Alpental pro-patrol did observe local east winds at Snoqualmie Pass building thin wind slabs over weaker snow near treeline Sunday.  

The most recent snowpack and avalanche observations include shallow storm slab releases from Alpental pro-patrol during AM control work on Christmas and of a small skier triggered storm slab near treeline in the Crystal backcountry Saturday. Light snowfall on Sunday was not expected to significantly increase the storm hazard.

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.

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.