Avalanche Forecast
Regions: Cascades - North East.
Expect dangerous avalanche conditions on Thursday. Strong winds along with heavy snowfall will create unstable snow at upper elevations. This potent storm will drastically change the previous snow cover. Even small avalanches can cause injury if you take a ride through shallowly buried rocks, stumps or other ground hazards.
Discussion
We have limited information about the current snow and avalanche set up, but heres what we know: Washington pass did well with a few storms in late November, opening up opportunities to recreate on snow mainly near and above treeline. As of this writing, average snow depths of 15" to 30" can be found in the area. That is set to increase, perhaps double over the next couple of days. Along with potential instabilities within the storm layer, the snowpack structure does harbor some weak snow. The recently buried surface, and a layer of facets above a crust found roughly 12" up from the ground warrant closer inspection. Â
On December 10th, an observer reported reactive conditions within a wind drift on a north facing slope at around 6,000ft. Check his recent observation here. On December 8th, test results indicated sudden failures 12" from the ground on a southeast facing slope at 7,000ft above Blue Lakes Trailhead on weak snow above a crust near the ground. On December 7, an observer found a natural slab that was triggered from loose snow just above Blue Lake on a north facing slope at 6,400ft. This appears to have occurred on the same layer. This is enough information to warrant suspicion of persistent layers, and bears consideration as the storm tapers off into the weekend.Â
Snowpack Discussion
Regional Synopsis Coming Thursday, December 12, 2019
Avalanche Problems
Storm Slabs
Heavy snowfall overnight Wednesday and through the day Thursday, along with strong westerly winds are likely to create unstable slabs as the day progresses. The most dangerous areas may be found above 5,500ft, where more snow will accumulate, and the slopes are more exposed to wind drifting. You are likely to experience stormy weather, poor visibility, and quickly changing conditions in the mountains. If you do go out, look for signs of instability such as cracking, collapsing, and hollow sounding snow. It may be a good day to avoid going in to avalanche terrain altogether, steering clear from big features such as large bowls and chutes. It is still early season, and shallowly buried rocks, trees, and creeks abound.
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: Likely
Expected Size: 1 - 1