Avalanche Forecast

Archived

Apr 12th, 2018–Apr 13th, 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.

New snow and moderate winds will build fresh wind slabs throughout the day Friday. Avoid slopes greater than 35 degrees where you see blowing snow, snow drifts, or fresh cornices. At lower elevations rain will create wet avalanche conditions. Stay off of steep slopes where you see new rollerballs, fresh fan shaped debris, and during periods of intense rainfall.

Detailed Forecast

Expect new wind slabs to form throughout the day becoming larger and easier to trigger. 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 will develop wet surface snow conditions. Stay off of slopes greater than 35 degrees where you see new rollerballs, observe fan sharped avalanche debris, or during periods of intense rain. Loose wet avalanches have the ability to entrain large amounts of snow and may carry you into areas with higher consequences, such as trees, creeks or gullies.

Other spring hazards exist in the mountains. 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

Six inches (15cm) of moist new snow fell near Hurricane Ridge Wednesday afternoon into Thursday afternoon. Moderate south winds drifted the new snow in wind exposed areas. Observations indicate that the new 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.