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Avalanche Forecast

Archived

Apr 10th, 2018–Apr 11th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

Tuesday will be a transition day as we begin to enter a cooler snowier pattern. You may still encounter large and destructive Wet Snow avalanches at lower elevations, while fresh Wind Slabs develop near and above treeline. During this transition, continue to give fresh Cornices a large margin and minimize travel on slopes below.  

Detailed Forecast

On Tuesday, a frontal system will bring a rapid cool down with new snowfall accumulating above 4500-5000 ft by the afternoon. You may still trigger Loose Wet avalanches or they may be triggered by additional rainfall Tuesday morning. Watch for signs of wet snow conditions such as sluffing, roller-balling and any natural Loose Wet avalanches as signs of an increasing hazard. Loose Wet avalanches still have the ability to become large in areas where they gouge down to deeper layers of moist or wet snow. 

Shallow new Wind Slabs may form on lee slopes near and above treeline by the afternoon. Use visual clues such as fresh cornices, wind drifted pillows and cracks in the snow all indicating that you could trigger a Wind Slab avalanche. Strong winds will likely make for erratic loading patterns, suspect Wind Slabs may be present on all aspects. 

Large fresh cornices will still be fragile due to recent warm temperatures and initial rainfall Tuesday morning. Give cornices a large margin of safety and avoid travel on slopes below, as cornice failures may trigger large avalanches on slopes below.

Minimize or avoid exposure below unsupported slopes as the potential for Glide Avalanches will increase during prolonged rainfall and warm temperatures. 

Snowpack Discussion

Monday was warm with filtered sunshine. A strong storm over the weekend caused rain Saturday to high elevations followed by cooling and new storm snow of a foot or more by Sunday afternoon. The new snow was transported by periods strong winds that built fresh Wind Slabs on a variety of aspects, especially below ridges.

The recent storm grew fresh cornices along exposed ridges. 

Older weak snow has been observed on N-E aspects near and above treeline above a crust over the last 2 weeks. This layer is generally 1 to 1.5 feet (30-45 cm) below the snow surface. Rainfall and continued above freezing temperatures Friday night and Saturday may have allowed Wet Slabs to fail at this interface.

There are no other significant layers of concern in the snowpack at this time.

Observations

Park rangers reported about 1 ft of new snow as of Sunday morning.

On Friday 4/6, NWAC professional observer Matt Schonwald found the facets above a crust on NE aspects between 5200-5400 ft healing.  While this interface may have come into play with Wet Slabs Saturday, the Persistent Slab problem has ended. Matt also found glide cracks opening on the 20th of June path. Weak snow at the ground could allow the 3 ft (85 cm) of firmer snow above to fail as a Glide avalanche if thoroughly wetted. While he found other areas with glide cracks, they were not widespread. 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.