Avalanche Forecast
Regions: Snoqualmie Pass.
The avalanche danger you encounter Thursday depends on how much new snow you find. When you come across more than 8 inches of heavy storm snow or find the wind formed snowdrifts, steer around all open slopes greater than 35 degrees. If you discover evidence of strong over weak snow at lower elevations, you can expect the same issue to be larger and harder to manage as you ascend.
Discussion
This is a tricky avalanche forecast because it depends on additional snow associated with a Puget Sound Convergence Zone. This weather phenomenon can lead to high levels of spatial variability with some locations experiencing substantial rain/snow while areas nearby receive very little. The avalanche hazard you encounter will depend on your location in the zone and how the weather plays out Wednesday night.Â
Limited information, especially at upper elevations, around Snoqualmie Pass, leave us with a higher degree of uncertainty than normal for this time of year. Take time to make observations and compare them to the forecast. When conditions differ from what you expected, step-back and reevaluate.
Snowpack Discussion
New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.
Avalanche Problems
Storm Slabs
These may not look like your normal run of the mill storm slabs. Wind gusts at the top of Alpental exceed 100mph Tuesday night. However, temperatures fluctuated, intense precipitation occurred, and we continue to receive more snow. Even though the weather that formed these potential avalanches is complex, the solution is simple. When you find more than 8 inches of up-side-down storm snow or notice the wind drifted snow into thicker slabs, stay off of slopes greater than 35 degrees. When rain changes to snow (as it did in this storm), you may often find that any slab does not fail immediately above the rain crust, but rather an inch or two higher. You can use hand pits, up-track tests, and small slopes to investigate the new storm snow.
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