Avalanche Forecast

The incoming snow over the next 24 hours will thicken existing storm slabs. Look for density changes within the upper snowpack. These “strong over weak” layering configurations may exist, making storm slab avalanches easy to trigger on Friday. Plenty of snow is available for transport, and winds may blow snow and create thicker and more reactive slabs. Avoid fresh drifts and steer around areas where the wind has stiffened the snow on leeward slopes at mid and upper elevations. Continue to watch for loose dry avalanches - they could knock you off your feet or pile up debris deeper than you expect. Use small test slopes to assess how the new snow is bonding to itself and older snow layers.

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.

Near Washington Pass, a recently buried layer of facets may be found underneath the new snow. This layer looks to become a lasting problem. Look out for slab structure, especially in recently wind loaded areas, and check for weak snow underneath the slab. Step back and give the snowpack time to adjust while we collectively discover more about this recently buried layer.

We have less information about areas near, east, and south of Mazama. Persistent slab avalanches may be in play in these areas where recent snow may have fallen on a weaker snowpack. Watch for cracking, listen for collapses, or dig down to look for these layers of concern. If you can find layers of facets or surface hoar, all you need is a slab on top, and you have a recipe for dangerous avalanches.

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.