Avalanche Forecast
Issued: Apr 12th, 2018 11:01AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs, Storm Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Expect avalanche hazard to rise throughout the day as another storm impacts the Northeast Cascade zone. The exact avalanche problem will be dependent on elevation and proximity to the Cascade crest. Avoid opens slopes greater than 35 degrees at all elevations Friday.
Summary
Detailed Forecast
Avalanche hazard will rise Friday as a new round of precipitation impacts the Northeast Cascade zone. Expect avalanche problems to develop throughout the day, becoming larger and easier to trigger. Precipitation amounts will vary by location, expect the highest amounts in locations close to the Cascade crest such as Washington Pass. Avalanche hazard may be lower in areas farther east.
You will be able to trigger new wind slabs on lee slopes and cross-loaded features. Use visual clues such as blowing snow, fresh cornices, and snow drifts to identify and avoid steep wind loaded terrain.
As snow accumulates throughout the day, it will become possible for you to trigger storm slab avalanches. Warming temperatures along with the snow will create heavier stronger snow over lighter weaker snow. You are most likely to trigger storm slabs in very steep terrain, near convex rollovers, or on unsupported slopes.
At lower elevations rain will develop wet surface snow conditions. Stay off of slopes greater than 35 degrees after snow transitions to rain. If you see new rollerballs, observe fan shaped avalanche debris, or experience periods of moderate rain, limit your exposure to steep terrain above you where avalanches may initiate.
Other spring-time hazards exist in the mountains. Cornices, glide cracks, and open creeks can all pose a risk to backcountry travelers.
Snowpack Discussion
Generally warm weather over the last several days has allowed the upper snowpack to gain strength. Several freeze and thaw cycles have likely created a strong surface crust in many locations.
We have very limited information about older persistent weak layers in the Washington Pass area. While recent weather conditions have likely allowed many of these layers to gain strength, we do not have any direct recent observations. If you have any information on snowpack conditions consider sharing your observations with NWAC on our public observations page.
Two common persistent weak layers seen in the Northeast Cascades are:
- 3/25 and 3/22: Buried surface hoar layers found on shaded aspects near and above treeline.
- 2/13 Facets above a firm and thick melt-freeze crust can be found in many locations near and above treeline. This layer is thought to be dormant at this time but may re-awaken with a substantial weather input.
Lower elevations further east of the crest have melted back for the season and no longer present an avalanche risk.
Observations
No recent observations
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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
Expected Size
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.
Elevations: Below Treeline.
Likelihood
Expected Size
Valid until: Apr 13th, 2018 11:01AM
