Avalanche Forecast
Regions: Cascades - South West.
Changing weather will require careful snow and terrain evaluation west of the crest by Friday afternoon.
Detailed Forecast
A moderate front and short wave trough will cross the the Northwest on Friday afternoon and evening. Rain or snow should begin over the Cascades Friday afternoon.
Increasing winds and increasing snow mainly above and near treeline west of the crest should begin to build new wind and storm slab Friday afternoon. These new layers should still be fairly shallow by the end of the afternoon. The danger will be greater if the snowfall begins sooner or is heavier than expected by the end of the afternoon.
New wind and storm slab should continue to build Friday evening especially if convergence is significant near Stevens Pass.
Even though Friday should overall be cool and cloudy it is April and the sun is getting much stronger. So possible loose wet avalanches involving recent storm snow will remain in the forecast as well and emphasized for solar slopes.
Snowpack Discussion
Active weather and periods of snowfall have been seen since about mid March with some avalanche cycles and also periods of consolidation and stabilizing. The largest avalanche cycle was at Mt Rainier March 25th.
The latest front moved across the Northwest Tuesday followed by showers and rapid cooling Tuesday night and Wednesday. Storm snow from this system ranged from about 3-10 inches along the west slopes except at Snoqualmie with 15-20 inches in strong convergence Tuesday night.
A bit surprising has been the reports from ski patrols at Alpental and Crystal Mountain Wednesday that the new snow quickly settled with little to no avalanche activity. There was evidence at Alpental that a natural cycle occurred before daylight Wednesday likely during some heavy loading in the early morning hours.  A testament to how quickly new snow is able to settle and stabilize as we move into April. By Wednesday afternoon, the snow had settled 6 inches at the Snoqualmie Pass level from the early morning depths.
A cool to mild day on Thursday is mainly causing of consolidation and stabilizing. The Alpental patrol had no avalanches to report on the upper mountain on Thursday with recent surface snow getting heavy on solar slopes and staying cool and light on north slopes.
Snowpack problems west of the crest should remain in the upper or surface layers. 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 season. Many areas at the lowest elevations do not have enough snow to cause an avalanche danger.
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: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
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: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1