Avalanche Forecast

Weather models are uncertain about how much new snow will fall in the area, but it is likely that storm slabs will build through the day on Sunday. If you find more than 8 inches of new snow on the ground, you may be able to trigger storm slabs on open slopes greater than 35 degrees. You are most likely to experience these conditions in locations close to the volcano, at higher elevations, and in places where the wind drifted snow into thicker slabs. As the snow accumulates through the day avalanche danger will slowly rise.

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.

The most recent layer of buried surface hoar continues to get deeper in the snowpack as snow piles deeper. This layer has been gaining strength and is becoming harder to trigger. Recent rain in the area further reduced the extent of where we expect this persistent layer to exists. You might encounter buried surface hoar 4 ft or more below the snow surface on N-E aspects above 5500 ft. Buried surface hoar can release on surprisingly low-angle slopes. If you plan to travel into higher elevation terrain, take the time to consider and discuss this low-likelihood but high-consequence avalanche problem.

Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.

The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.

This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.

Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.