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Avalanche Forecast

Archived

Apr 2nd, 2015–Apr 3rd, 2015

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

Regions

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Changing weather will require careful snow and terrain evaluation east of the crest Friday afternoon.

Detailed Forecast

A moderate front and short wave trough will cross the the Northwest on Friday afternoon and evening. Rain or snow should begin over the Cascades Friday afternoon.

Increasing winds and increasing snow mainly above treeline east of the crest should begin to build new wind and storm slab Friday afternoon. These new layers should still be fairly shallow and mainly above treeline east of the crest by the end of the afternoon. The danger will be greater if the snowfall begins sooner or is heavier than expected by the end of the afternoon.

New wind and storm slab should continue to build Friday evening especially downwind of possible convergence near Stevens Pass.

Even though Friday should overall be cool and cloudy it is April and the sun is getting much stronger. So possible loose wet avalanches involving recent storm snow will remain in the forecast as well and emphasized for solar slopes.

Snowpack Discussion

Active weather has been seen since about mid March but there has been little snowfall overall east of the crest. So consolidation and stabilizing has been mainly seen east of the crest the past couple weeks.

However during the fair and mild weather Monday, DOT avalanche professionals working in the Washington Pass area triggered significant slides Monday using explosives. Wet slab avalanches entrained moist snow in the Liberty Bell paths and buried the closed highway with about 8 feet of debris. But little natural avalanche activity was observed in the area. 

The latest front moved across the Northwest Tuesday followed by showers and rapid cooling Tuesday night and Wednesday. But this caused little snow east of the crest.

Snowdepths vary greatly across the east slopes with a regionally healthy snowpack in the northeast Cascades to bare solar and lower elevation slopes in the central and southeast Cascades. Many areas at lower elevations and further away from the Cascade crest do not have enough snow to cause an avalanche danger.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.