Avalanche Forecast

The Pass is several days into a prolonged spring cycle with gradually warming temperatures and loose wet avalanches. We still haven’t seen a big “shed” of loose wet slides. Instead, a few more occur each day. This pattern should continue on Thursday. Expect clear skies and cool temperatures overnight to help the snow surface freeze and limit the loose wet hazard. Sunshine will quickly warm temperatures in the morning and begin to soften the frozen surface. When you notice that your boot sinking past the ankle (about 4”), you’re moving from “soft” too weak and unstable. It’s time to change aspects and seek out slightly firmer snow. As you plan your day, consider the slopes you’ll need to cross to return to your car and how they may react in the heat of the afternoon.

This snowpack has not transitioned to spring and many cold dry layers and crusts still exist. As this warm stretch continues, we’re starting to think about how water may affect these layers and potentially produce deeper slab and glide avalanches. Be leery of large sunny complex slopes during the heat of the day.

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.

Large cornices loom over numerous alpine slopes and this springtime pattern is making them weak and saggy. On Thursday, you could see them begin to fail. Choose routes that minimize the time you spend below these huge blocks. They may be in the sun, even while you shiver in the shade. A collapsing cornice or other avalanches can act as a very large trigger for slopes below, causing slides to break into deeper layers. 

Cold dry snow continues to hang on at upper elevations and in steep shaded terrain. When you move into winter-like areas, take a second to refocus your attention and look for signs of wind affected snow. Small isolated pockets of wind slab were seen Wednesday near Mount Roosevelt and likely exist in other locations. Evaluate your line carefully for signs of wind loading prior to committing to a slope.

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.