Avalanche Forecast

A poor snowpack structure is to be found in areas on the eastern slope. If you hit the wrong place in the snowpack, it could result in a very large and dangerous avalanche. Large triggers are more likely to initiate a persistent slab. Steep, unsupported slopes with recent wind loading are the most likely terrain where these can occur.

The best way to reduce the risk of this high consequence situation is to minimize your exposure to slopes capable of producing large avalanches.

-Choose not to trust steep slopes.

-Attempt to put a significant distance in between where you are traveling and where avalanches start, run, and stop.

-Don’t underestimate how far and wide these could run when identifying safer areas to stop and regroup.

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.

The most dangerous slopes will be at upper elevations where thick slabs may have formed from deeper accumulations and wind. Stay off of steep slopes near and above treeline if finding these slabs. The storm snow is sitting on variable old snow surfaces, from low density cold snow to hard wind slabs. This bonding may be variable between the storm snow and the old snow surface. Carefully evaluate the new snow depth, it’s cohesiveness, and how it is bonding before choosing to travel in avalanche terrain. Use small, inconsequential slopes and tests to check if the storm snow will slide.

Any avalanche in the storm snow layers may break into deeper, old snow layers. 

Small loose wet avalanches may become likely in the afternoon on steep, southerly aspects. Limit your time spent on steep slopes during the middle of the day, and if noticing roller balls or recent loose avalanches. 

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.