Avalanche Forecast
Regions: Snoqualmie Pass.
A spring mix of avalanche problems will be possible Saturday with new storm and wind slab concerns near and above treeline, and loose wet possibilities on steeper solar aspects in the afternoon. There's a fair amount of uncertainty with the forecast Saturday, so be attuned to quickly changing snow conditions, especially if traveling above treeline.
Detailed Forecast
A frontal system passing through Friday night should bring light to moderate rain and snow along with a cooling trend by Saturday morning.  Post frontal showers could locally be intense as the air mass destabilizes Saturday morning. Moderate SW winds will transport snow onto lee easterly aspects near and above treeline.Â
Despite the cooling trend, there should be some shallow storm and wind slab near treeline by Saturday morning. New snow that does accumulate will be susceptible to potential sunbreaks later Saturday afternoon, so use extra caution on steeper solar slopes above treeline. Locally intense showers Saturday could contain graupel and quickly lead to sensitive storm slabs.Â
Less recent snow and ample terrain anchors should greatly limit the avalanche danger below treeline.Â
Remember the NWAC forecast applies to elevations up to the Cascade crest (~7000 to 8000 ft). Significant new snowfall from late this week likely poses a higher avalanche danger at these elevations in the Mt. Baker area.  Â
Due to the low snowpack, especially below treeline, watch for terrain hazards such as open creeks, partially covered rocks and vegetation. Many areas below treeline do not have enough snow to cause an avalanche danger.
Snowpack Discussion
During the storm cycle the weekend of March 14-15th, several inches of water fell with new snow above 6000-7000 ft in the south Cascades and above 4500 ft in the north Cascades. Natural or skier triggered slides that occurred Sunday or Monday were generally loose wet size D1-D2, and to a lesser extend storm slabs, and reported throughout the west slopes of the Cascades relative to last weekend's snowline.
A few inches of snow accumulated along the west slopes of the Cascades Tuesday above 5000 feet. Observations on Wednesday noted small loose wet avalanches involving the new storm snow near and above treeline.Â
More significant new snowfall likely accumulated above 6000Â feet in the Mt. Baker area Thursday and Friday, but there have been no recent observations in this terrain.Â
The Chinook DOT crew on Monday found debris from an natural cycle of loose or storm slab avalanches from Sunday.
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You are likely to encounter debris from last weekend if traveling above 6000 ft this weekend. Photo J. Stimberis.
The snowpack at low elevations remains meager to non-existent with the average snow-line around 4500 feet along the west slopes. The mid and lower snowpack west of the crest consists of layers of stable consolidated rounded grains or melt forms and crusts from multiple warm periods this winter.
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
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: North, North East, East, South East.
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: South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1