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Avalanche Forecast

Archived

Feb 11th, 2015–Feb 12th, 2015

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

Regions

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Although less likely, the primary avalanche problem Thursday will continue to be loose wet avalanches.

Detailed Forecast

Mild snow levels will prevail again on Thursday with light rain developing for the central and north Cascades. There may be a few sunbreaks for the south Washington Cascades Thursday. 

Loose wet avalanches are possible Thursday on steeper slopes near and above treeline that either receive enough rainfall, or in areas further south, solar aspects that receive substantial sun breaks. If neither happen, the loose wet avalanche potential would be minimal.   

Lingering wind slab will be listed as a problem for one more day west of the crest above treeline. Watch for firmer wind transported snow on previous lee slopes mainly on N-SE slopes near ridges.

As a result of the overall low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation.

Snowpack Discussion

The latest atmospheric river to impact the Pacific Northwest brought several inches to around a foot of water to the west slopes last week; unfortunately it fell mostly in liquid form. This lead to significant settlement and at lower elevations, continued melting of the seasonal snowpack.   

About 5-12 inches of heavy snow was seen near and above treeline the past couple days west of the crest based on weather station data and reports.

Signs of loose wet activity that began Tuesday was dampened by extensive high cloud cover on Wednesday. Despite the continued warmth and high freezing levels, several NWAC observers along the west slopes Wednesday reported no avalanche activity in the below and near treeline zones. The most recent storm snow in the upper snowpack near treeline was reported as wet and well bonded to the previous rain crust.  

The mid and lower snowpack west of the crest should consist of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.

Problems

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.

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.