Avalanche Forecast

We’re deep into a prolonged spring-time pattern and loose wet avalanche cycle. Each evening, cold clear nights help the snow surface freeze and limit the loose wet hazard. During the day rapidly warming temperatures and a strong sun weaken the surface and drive the potential for more loose avalanches. Information about the extent of a natural loose wet cycle in the West-South has been limited this week. A few observations reported human triggered loose slides in the Crystal backcountry on Wednesday. When you see your boot sinking into the wet surface past your ankle (about 4”), conditions are changing from “fun and soft” to “weak and unstable.” Seek out slightly firmer, less sun affected snow by changing aspects. As you plan your day, consider what slopes you’ll need to cross to return to the trailhead and how these areas may react later in the afternoon. 

Even after 5 days of warm weather, below the surface, the snowpack still resembles mid-winter, with several dry layers and firm crust. It’s hard to say how or when avalanches could fail as water reaches these layers. Be leery of large complex sunny terrain during the heat of the day where you’re most likely to see a deeper slab or glide 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.

A wet and stormy winter built large cornices that now loom over many alpine slopes. This warm stretch of weather may cause these frozen waves to sag and collapse. Choose routes that minimize the amount of time you spend below these precarious blocks of snow. While you could see a cornice on any aspect, the largest seem to exist on NE-E terrain. Remember, even while you may shiver in the shade, cornices, and slopes above you may be feeling the full warmth of the sun. A collapsing cornice, or any avalanche, could trigger a large, deep slide on the slopes below. 

You may still find cold dry snow at upper elevations and on steeper shaded slopes. When you transition into these winter-like areas, turn your attention to wind affected snow. Take time to carefully assess your line for any evidence of wind loading prior to committing to the terrain.

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.

A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.

Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.