Avalanche Forecast

New snow accompanied by strong winds will create storm slabs at all elevations. The incoming snow may not bond well to the old snow surface. Be especially careful of leeward areas below ridges and cross-loaded slopes. Any triggered avalanche within new snow has the potential to break further down in the snowpack creating a much larger, wider, more dangerous avalanche. Watch for recent avalanches, shooting cracks, and collapses. Seek out low-angle supported terrain away from overhead hazard.

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.

These avalanches could break near the ground and act in surprising ways. You may be able to trigger them remotely, from low-angle terrain or adjacent slopes. You may see signs of instability such as recent avalanches, snowpack tests that show propagation, collapses, or cracks that travel away from where you impact the snow. Give yourself a wide safety buffer to address the uncertainty. This dangerous problem continues to deserve a high level of respect and caution.

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.