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Avalanche Forecast

Archived

Jan 6th, 2016–Jan 7th, 2016

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

Snoqualmie Pass.

In specific areas, where the most recent storm snow is more cohesive, small human-triggered slab avalanches will be possible. Before committing to a slope, think about the consequences of the terrain if even a small avalanche occurred. Newly formed wind slab is more likely in the Snoqualmie Pass area and south, near and above treeline, on a variety of aspects.  

Detailed Forecast

In general, the most recent storm snow overlying recently buried weak layers is lacking widespread cohesion to be deemed likely to trigger. In specific areas, where the storm snow is more cohesive, small human-triggered slab avalanches will be possible. Before committing to a slope, think about the consequences of the terrain if even a small avalanche occurred. Note density changes in the upper snowpack throughout the day and as you change aspect and elevation.  

Wind slab formed last week loaded lee west slopes as well as cross-loaded a variety of other aspects. Moderate E-SE winds in the Paradise, Crystal, and Snoqualmie areas may have built new shallow wind slabs over the last day or two in the near and above treeline zones. Look for signs of firmer wind transported snow that can indicate wind slab layers.

Snowpack Discussion

Fair weather occurred for almost a week around the New Year leading to extensive consolidation and stabilizing of the heavy snow from December. It also led to extensive surface hoar and near surface faceted snow on non-solar sheltered slopes according to reports for west and east of the crest in the Washington Cascades. On solar aspects, a sun crust formed during the stretch of high pressure. 

Moderate to strong east winds seen around New Years Eve through the weekend built wind slab on west aspects, primarily in the central and south Cascades including the Cascade Passes. A hiker was killed by a natural or triggered wind slab on Granite Mountain near Snoqualmie Pass Thursday, likely due to a wind slab avalanche on a west facing slope near treeline. Other skier triggered wind slab avalanches were reported near Paradise and Snoqualmie on north to west aspects last Thursday and Friday as well.

A pattern change beginning Sunday led to moderating temperatures and light snowfall Sunday through early Wednesday morning, with about 6-12 inches along the west slopes. This new snowfall accumulated on the surface hoar and near surface faceted snow from around the New Year on many non-solar or sheltered slopes. While a few reports via the NWAC observation page confirm the new snow failing on these recently buried weak layers, Pro-patrol reports along the west slopes generally reported the new snow lacking cohesiveness and unlikely to propagate in snowpack tests or during control work.

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.

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 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.