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Avalanche Forecast

Archived

Jan 17th, 2016–Jan 18th, 2016

Alpine
Natural avalanches possible, human triggered probable.
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

Olympics.

Even with an overall stabilizing trend on Monday, dangerous avalanche conditions may persist on lee wind-loaded slopes above treeline and where storm slabs remain sensitive to human triggering. Take it slow on Monday and evaluate the snowpack as you travel conservatively through the terrain.  

Detailed Forecast

Light showers should taper off Monday morning and a few sunbreaks are possible late morning before cloud cover increases early Monday afternoon ahead of the next frontal system. 

Wind slab should be found mainly on lee north to east slopes near and especially above treeline. Generally avoid wind loaded slopes above treeline.  

Storm slabs may become more cohesive and likely to trigger with day-time warming and some sunshine. Choose lower angled slopes if you find sensitive storm layers.  

Small loose wet avalanches should be likely on steeper slopes below treeline involving small amounts of recent storm snow. Watch for loose wet avalanches near terrain traps, where even a small avalanche could have unintended consequences. 

Snowpack Discussion

Deep storm snow that fell during mid-late December is well settled, homogeneous and has stabilized so the current avalanche danger focus will be on the upper snowpack. Fair weather over the New Year caused extensive surface hoar and near surface faceted snow that was buried by about 6 inches of snowfall at Hurricane from January 3-6th. An active and mild pattern over the last week has most likely eliminated any persistent weak layers like those found in the Cascades. Avalanche concerns should be limited to recent storm snow. 

The latest period of snowfall has been from about January 11-17th. The NPS rangers have reported about 6 inches of new snowfall over the weekend along with fluctuating snow levels.  

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.