Avalanche Forecast

Don’t overlook the huge volume of water we just received in a relatively short amount of time. Human-triggered avalanches are possible near and above treeline, where the snow is drier and deeper. Use caution on slopes steeper than 35 degrees, and steer clear of convexities, wind-loaded terrain, or unsupported slopes where you could trigger avalanches more easily. As temperatures continue to cool and more time passes, these avalanches will become less likely. 

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.

Recent very large and destructive avalanches prove this persistent weak layer survived the storm loading in some areas. Avoid traveling on large steep slopes above 5800’ on W-N-E aspects. Snowpits and crown profiles identified a layer of weak snow grains associated with a thin crust about a foot above the ground. Persistent slabs are difficult to assess, but if you trigger an avalanche it could be 3-6ft deep, break on slopes as low as 30 degrees, and wrap around features in the terrain. While snowpack tests can confirm this layer’s presence, they can not prove its absence. Don’t rely on a snowpit to interpret stability. This layer and these events have only been confirmed in the Crystal region. We don’t know if this layer exists in other areas, please submit your observations to our website.

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.