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Avalanche Forecast

Archived

Apr 13th, 2018–Apr 14th, 2018

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

Regions

Olympics.

Recently formed wind slabs exist at higher elevations and new wind slabs may form, particularly Saturday afternoon. Avoid slopes greater than 35 degrees where you see blowing snow, snow drifts, or fresh cornices. At lower elevations rain will continue to create wet avalanche conditions. Stay off of steep slopes where you see new rollerballs, fresh fan shaped debris, or crevasse-like cracks in the snow.

Detailed Forecast

Fresh wind slabs will build Saturday afternoon on northerly aspects as snowfall and winds increase, adding onto the shallow recent wind slabs formed due to moderate winds transporting 6-8" of snow from the previous 48 hours.  You can use visual clues to identify wind loaded slopes. Blowing snow, snow drifts, and fresh cornices all indicate that wind slabs may exist in nearby terrain. Avoid slopes greater than 35 degrees where you see wind loading has occurred.

At lower elevations, rain has saturated snow near the surface and cooling Friday night may not be sufficient to consolidate the snow. Where you encounter heavy rain or wet snow surface conditions, indicated by roller balls or fan-shaped avalanche debris, stay off of slopes greater than 35 degrees. Loose Wet avalanches have the ability to entrain more snow than you might expect and may carry you into areas with higher consequences, such as trees, creeks or gullies.

Other spring hazards exist in the mountains. As water drains the snowpack, Glide avalanches are possible on slopes with smooth ground surfaces. Minimize your exposure to slopes with crevasse-like glide cracks. Glide avalanches are difficult to predict and can occur without warning.

Recent warm weather and rain resulted in many creeks beginning to open. Be cautious if your intended route takes you over larger creeks as snow bridges may have grown thin and weak.

Snowpack Discussion

An inch or two of new snow is expected to have fallen at Hurricane Ridge Thursday night through Friday at higher elevations, adding to six inches (15cm) of moist snow that fell Wednesday afternoon into Thursday afternoon. Rain likely mixed with snow on Friday during the mid-day hours into the near treeline elevation band. Moderate south winds drifted the new snow in wind exposed areas Wednesday and are likely to have continued drifting the snow on Friday. Observations indicate that the recent snow fell on an underlying strong and supportable crust.

The upper snowpack generally consist of layers of melt-form snow and strong rounded grains. This has produced a strong snowpack without any layers of concern.

Older weak snow had been observed on N-E aspects near and above treeline. Small facets were found just above a crust about 1.5 ft (45cm) below the snow surface. This interface is likely no longer an issue due to recent rain and warm temperatures. 

Observations

On Thursday NPS Rangers reported 6” (15cm) of heavy new snow over the most recent crust (4/11). The recently formed crust was strong and supportable.

On Friday 4/6, NWAC professional observer Matt Schonwald found glide cracks in isolated areas. The snowpack on solar aspects is becoming patchy, especially below treeline. 

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 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.