Avalanche Forecast
Regions: Stevens Pass.
New snow should require careful snow and terrain evaluation west of the crest Saturday.
Detailed Forecast
Weak flow and mostly light showers should move out of a low or form over the Northwest in a cool slightly unstable air mass Saturday afternoon. These showers may be more likely during the afternoon hours near the volcanoes.
Watch for possible new shallow wind and storm slab from Friday. These layers would be deeper if you find an area that has more snowfall such as on a volcano or near Stevens or Snoqualmie if there is significant convergence.
It is April and the sun is getting much stronger. So possible loose wet avalanches will remain in the forecast as well. Solar slopes in any area with significant new snow from Friday will be very susceptible on Saturday.
Cornices won't be listed as an avalanche problem but use caution on slopes below cornices and on ridges where it can be hard to know if a cornice is present.
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.
A front moved across the Northwest Tuesday followed by showers and rapid cooling. 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 small natural cycle occurred at Alpental likely during heavy loading early Wednesday. But overall the new snow came with little to no avalanche activity.
A cool day on Thursday mainly caused consolidation and stabilizing. The Chinook DOT crew reported some snowballing on solar slopes and 8-10 inches of cool snow on north slopes.
Another front and short wave trough are crossing the Northwest Friday afternoon. This should be accompanied by moderate southwest winds and mostly light to moderate rain or snow in the Cascades. Snow showers should decrease pretty rapidly Friday evening. A couple to a few inches of new snow should be seen west of the crest. Stevens or Snoqualmie could end up with some extra snow showers in convergence Friday evening.Â
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 low 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: East, South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1