Avalanche Forecast
Regions: Olympics.
Dangerous wet snow conditions will develop Friday night and Saturday. Avoid avalanche terrain if you see slab avalanches in areas of wet snow. Minimize your exposure to large avalanche terrain from above. Avoid slopes with terrain traps where even a small Loose Wet avalanche would have serious consequences. Shallow Wind Slabs may build above treeline late in the afternoon.
Detailed Forecast
Rainfall late Friday night and Saturday morning will be followed by a cooling trend with snow levels falling to 5000-5500 feet in the afternoon. Windy conditions should also develop Saturday.Â
Large and destructive Wet Slab avalanches are likely Saturday, especially near and above treeline. One potential bed surface is the former Persistent Slab interface found on N-E aspects near and above treeline about 1-1.5 down. These avalanches may run naturally or be human triggered. Watch for liquid water reaching buried crusts or softer layers of snow, well-below the snow surface as a sign that Wet Slab avalanches could occur. Wet Slabs are dangerous because they are hard to predict, give little warning, and can be very destructive. If you see slab avalanches in areas of wet snowpack, avoid traveling in avalanche terrain. You may be able to trigger smaller Loose Wet avalanches more easily in the same types of terrain where the Wet Slab problem exists. Avoid slopes with terrain traps where even a small Loose Wet avalanche would have serious consequences.
Large or very large glide avalanches are possible in isolated areas with a smooth rock bed surface. In these specific terrain features, the entire snowpack may release if lubricated with water due to recent rainfall and sustained periods of above freezing temperatures. Look for glide cracks as a precursor that large and dangerous natural glide avalanches are possible. Glide avalanche releases are not tied to peak warming or rainfall and are difficult to predict. Â
Recent rain and warm temperature have weakened Cornices. Give Cornices a wide berth if traveling along ridgelines as they often break back further than expected. Be aware of overhead hazard if traveling on slopes with Cornices above as they may fail naturally or be human-triggered.Â
Rain will change to snow Saturday afternoon near and above treeline. Wind and new snow will form shallow Wind Slabs on lee slopes near and above treeline. Visual clues such as blowing snow, fresh cornices, and cracks in the snow all indicate that you could trigger a Wind Slab avalanche.Â
Snowpack Discussion
Periods of light rain and mild temperatures have caused wet snow conditions to extend into the above treeline terrain in the Hurricane Ridge area.
On Wednesday, shallow amounts of wet snow accumulated above about 5000 ft.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 allow Wet Slabs to fail at this interface.
There are no other significant layers of concern in the snowpack at this time.
Observations
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 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 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
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
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.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1