Avalanche Forecast
Regions: Olympics.
Shallow storm slabs found mainly above treeline Sunday may be sensitive to human triggering. Despite the cool weather Sunday, brief sunbreaks could cause small loose wet avalanches on steeper solar slopes.
Detailed Forecast
A frontal system passing through the Cascades Saturday night will bring light amounts of new snow to mid and higher elevations late Saturday night through Sunday. The avalanche forecast will slightly differ by zone based on expected new snow amounts, with the most snow expected in the northwest Cascades but little new snow expected along the east slopes of the Cascades. Â
Shallow storm slabs are possible mainly above treeline Sunday. Due to the refreezing snow surface and a cooling trend, new snow should generally bond well to wet snow or rough surface crusts. However, due to the showery regime in the cold air mass overhead Sunday, graupel layers are a probable bed surface for shallow storm slabs. Wind slab will not be specifically listed, but with light to moderate westerly transport winds, expect some loading on lee slopes above treeline.  Â
Due to the cooling trend and cloudy skies expected, small loose wet avalanches should be unlikely except on isolated steep slopes at lower elevations or during sunbreaks on solar aspects. Watch for terrain traps that might funnel even shallow, loose snow, such as gullies and creeks.Â
The potential for cornice releases will diminish, but still remain a possibility through the weekend. Cornice releases are very unpredictable, so avoid areas below cornices and remember that cornices can break much further back than expected along ridges.
Although not listed as an avalanche problem, powerful glide avalanches can release unexpectedly so also avoid areas below steep unsupported slopes or rock faces, especially if they are showing glide cracks.
Snowpack Discussion
Weather and Snowpack
On Friday we began our slow transition from unusual April warmth to a cooler and unsettled pattern. Saturday featured mostly cloudy skies and occasional light showers for the west slopes of the Cascades, Olympics and Mt. Hood area while the eastern slopes away from the Cascade crest saw mostly sunny skies.Â
For most of last week, freezing levels had averaged near or above 10,000 feet with strong spring sunshine. This was the third period in April with freezing levels above 10,000 feet. The cumulative effect of the warm stretches have helped establish good melt water drain channels in the snowpack with much of the lower elevation snow continuing to melt away and generally transitioned us to a homogeneous spring snowpack throughout the region.Â
Storms in March built unusually large cornices along many ridges. While these have been melting back, many have failed recently, producing small and large wet snow avalanches on slopes below during the recent warm weather. The potential for low probability/high consequence encounters, such as cornice failures and glide avalanches from steep unsupported slopes and smooth rock faces, will continue this spring.Â
The mid and lower snowpack should generally be a stable mix of crusts and layers of moist and rounded snow crystals.
Recent Observations
The most recent observation from the Hurricane Ridge area came from Matt Schonwald on Saturday 4/16 and indicated there was no longer enough snow in the below treeline band to be an avalanche problem and even within the near treeline band, avalanches were confined to specific terrain features.Â
After another week of hot weather, the melt back of the snowpack has continued to diminish the threat of avalanches in this area.
Watch for cornices and possible shallow wet snow conditions in areas that are maintaining a more significant snowpack.
Avalanche Problems
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
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: Alpine, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1