Avalanche Forecast
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.Â
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.Â
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.Â
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.Â
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.Â
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1