Avalanche Forecast

Heavy snowfall will build fresh storm slabs over the next 24 hours. Avalanches are very likely within the new snow. Wind-loaded terrain at upper elevations will develop thicker and more reactive slabs. Avalanches involving new snow have the potential to step down and trigger deeper weak layers in the snowpack. Storm slabs will become more problematic throughout the day as temperatures cool and more snow accumulates. Watch for shooting cracks, collapses, and recent avalanches. Give the storm snow time to stabilize. Avoid travel near and below avalanche terrain.

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.

Expect wet loose avalanches on steep slopes at mid and low elevations. Avoid travel in avalanche terrain during periods of heavy rain. As wet avalanches run downslope, they could entrain large amounts of snow and even trigger slab avalanches. Look for roller balls and pinwheels as indicators of weakening snow surfaces. Avoid gullies and other confined terrain features where debris could pile up and increase the consequences of even a small avalanche. 

Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.

Several loose wet avalanches, and lots of pinwheels and roller balls.

Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.

New snow and wind will thicken existing slabs resting on a layer of feathery surface hoar that formed around Christmas. Recent observations from this area indicate the surface hoar has a spotty distribution and can be hard to find. Regardless, impressive and unusual recent avalanches still have us concerned. This layer can be found in the upper snowpack between 4500-5500ft primarily on north and east aspects. Be especially mindful of steep slopes near treeline that are sheltered from the wind. Let the snowpack adjust as it experiences rapid change over the next 24 hours.

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.