Avalanche Forecast

Loose wet avalanches are likely on steep slopes at all elevation bands. Avoid travel in avalanche terrain if you witness heavy rain falling on dry snow. 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.

Heavy snowfall paired with strong and gusty winds will redistribute snow and build fresh wind slabs. You will encounter the problem above treeline on the lee side of ridges and on cross-loaded slopes and terrain features. Work to identify wind-drifted snow by paying close attention to sudden changes in snow surface texture and hardness. Stick to sheltered slopes or wind-scoured areas. Avoid travel on or underneath unsupported wind-loaded slopes 35 degrees and steeper.

Release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.

Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..

Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

We are closely tracking the deep persistent slab problem in neighboring areas, but have limited observations directly from the West Slope Central zone. Be conservative with your terrain selection if you travel in this area given the uncertainty. Another round of rain, snow, and wind will test this layer again on Saturday.

You are most likely to encounter this problem on north and east aspects above 5000ft where a layer of surface hoar and facets is buried 4-7ft deep. Carefully evaluate the snowpack before entering larger avalanche terrain and venturing into higher elevations.

Deep persistent slabs are difficult to assess and predict. Our current situation still requires patience. Visible crowns of very large avalanches are stark reminders of the dangers that may lurk deep within our upper elevation snowpack. It has been several days since one of these avalanches occurred, and uncertainty remains regarding the sensitivity of this problem. Although triggering a deep persistent slab avalanche is unlikely, the consequences of being caught in one remain very high.

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply buried over time.

Deep Persistent Slabs avalanches can be destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.

A snowboarder triggered this Deep Persistent Slab near treeline, well down in the path.

Deep, persistent slabs are destructive and deadly events that can take months to stabilize. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Give yourself a wide safety buffer to handle the uncertainty, potentially for the remainder of the season.