Avalanche Forecast
Issued: Jan 6th, 2016 10:04AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs, Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
In specific areas, where the most recent storm snow is more cohesive, small human-triggered slab avalanches will be possible. Before committing to a slope, think about the consequences of the terrain if even a small avalanche occurred. Newly formed wind slab is more likely in the Snoqualmie Pass area and south, near and above treeline, on a variety of aspects.
Summary
Detailed Forecast
In general, the most recent storm snow overlying recently buried weak layers is lacking widespread cohesion to be deemed likely to trigger. In specific areas, where the storm snow is more cohesive, small human-triggered slab avalanches will be possible. Before committing to a slope, think about the consequences of the terrain if even a small avalanche occurred. Note density changes in the upper snowpack throughout the day and as you change aspect and elevation.
Wind slab formed last week loaded lee west slopes as well as cross-loaded a variety of other aspects. Moderate E-SE winds in the Paradise, Crystal, and Snoqualmie areas may have built new shallow wind slabs over the last day or two in the near and above treeline zones. Look for signs of firmer wind transported snow that can indicate wind slab layers.
Snowpack Discussion
Fair weather occurred for almost a week around the New Year leading to extensive consolidation and stabilizing of the heavy snow from December. It also led to extensive surface hoar and near surface faceted snow on non-solar sheltered slopes according to reports for west and east of the crest in the Washington Cascades. On solar aspects, a sun crust formed during the stretch of high pressure.
Moderate to strong east winds seen around New Years Eve through the weekend built wind slab on west aspects, primarily in the central and south Cascades including the Cascade Passes. A hiker was killed by a natural or triggered wind slab on Granite Mountain near Snoqualmie Pass Thursday, likely due to a wind slab avalanche on a west facing slope near treeline. Other skier triggered wind slab avalanches were reported near Paradise and Snoqualmie on north to west aspects last Thursday and Friday as well.
A pattern change beginning Sunday led to moderating temperatures and light snowfall Sunday through early Wednesday morning, with about 6-12 inches along the west slopes. This new snowfall accumulated on the surface hoar and near surface faceted snow from around the New Year on many non-solar or sheltered slopes. While a few reports via the NWAC observation page confirm the new snow failing on these recently buried weak layers, Pro-patrol reports along the west slopes generally reported the new snow lacking cohesiveness and unlikely to propagate in snowpack tests or during control work.
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: All elevations.
Likelihood
Expected Size
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
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: All elevations.
Likelihood
Expected Size
Valid until: Jan 7th, 2016 10:04AM
