Avalanche Forecast

Issued: Dec 10th, 2018 10:15AM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Loose Wet.

Northwest Avalanche Center NWAC, Northwest Avalanche Center

Dangerous avalanche conditions will develop quickly on Tuesday. Avalanches are likely due to significant new snow and wind, especially near and above treeline. Due to early season conditions, small avalanches have a greater potential for injury due to exposed rocks and vegetation. 

Summary

Snowpack Discussion

Regional Synopsis coming soon. 

Problems

Storm Slabs

An icon showing Storm Slabs

Storm slabs will quickly build and become sensitive to human triggering Tuesday.  Larger, more destructive slabs are possible near and above treeline, especially on wind loaded slopes.  

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

Very Likely

Expected Size

1 - 1

Loose Wet

An icon showing Loose Wet

Loose wet avalanches will occur in the afternoon as snow turns to rain below treeline. They may entrain new snowfall received earlier in the storm. Even small avalanches can be dangerous when combined with terrain traps like cliffs or exposed early season hazards. 

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

Very Likely

Expected Size

1 - 1

Valid until: Dec 11th, 2018 10:15AM