Avalanche Forecast

We’re a few days into this springtime cycle and several loose wet avalanches already occurred. Monday’s initial warm-up likely caused the bulk of the natural activity, however, you could still see a few more avalanches from slopes that haven’t already slid. Even though the air temperatures may not dip below freezing in some areas, clear skies should allow the snow surface to freeze, minimizing avalanche danger in the morning. It won’t take long for the sun and rapidly warming temperatures to soften the snow surface. When you find your boot sinking in past the ankle, its time to change to aspects with snow that’s slightly more frozen. Expect the snow to weaken first on easterly aspects and move around the compass dial as the day progresses. Take time to think about what slopes you’ll need to cross to return to your car later in the day and how they may be affected by the warming snow. 

On Wednesday we’ll be entering our 3rd day of above freezing temperatures and we’re starting to think about how water may impact other layers in the snowpack. As water works its way deeper, you could see an isolated larger slab or glide avalanches. It may be best to limit you exposure to large complex terrain during the warmer parts 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.

A look around the ridgelines near the Pass will quickly remind you that cornices have grown large and looming after a full winter. Now, during this warm spell, we’re worried about them falling down. Choose routes that minimize the amount of time you spend below these ticking time-bombs. Falling cornices, or any avalanche, could act as a trigger for larger deeper slabs. Recently, a cornice failed in the upper Chair Peak basin triggering a large wind slab on a north-facing slope below. Even though the slope was in the shade, the top of the cornice was in the sun. 

Observations from the Pass continue to confirm that soft dry snow is hiding in the shadows of steeper northerly slopes. In these locations, think about wind affected snow. Numerous wind slabs were triggered over the weekend in similar terrain. Evaluate steep and complex lines for signs of wind loading before committing to the 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.