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Avalanche Forecast

Archived

Dec 25th, 2014–Dec 26th, 2014

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

Regions

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Watch for wind slab on lee slopes near and above treeline especially due to more loading on southerly aspects than usual. Loose sluffs should be manageable except be wary on steeper slopes near terrain traps. 

Detailed Forecast

Isolated snow showers, increasing high clouds, light W-NW winds and cool temperatures should do little to change the avalanche danger Friday. Watch for wind slab on lee slopes near and above treeline. NW winds have likely loaded southerly aspects more than usual. Loose sluffs should be manageable except be wary on steeper slopes near terrain traps. 

 

Snowpack Discussion

The frontal system that impacted the area Tuesday through Wednesday morning started warm and ended cold for a right side up layering. New snowfall generally ranged 6-12", with lower amounts near Snoqualmie.  Winds turned northwesterly with the cool-down... loading SE aspects Wednesday. A few inches of new snow accumulated Wednesday night and Thursday. 

On Wednesday, NWAC Pro-observer Jeff Hambelton in Mt. Baker area found a right-side upper snowpack. Moderate wind transport had created a stiffer layer of snow on some lee slopes near and above treeline and observed small loose dry sluffs -  Watch Jeff's video.  

Moderate NW winds and light snow showers on Thursday continued to load lee slopes. 

The lower snowpack is generally strong and comprised of crusts and polycrystals.  

If traveling to the east slopes of the Cascades be aware of the different snowpack structure containing persistent weak layers and read the avalanche forecast. 

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.