Avalanche Forecast

We don’t have any direct observations from the West South zone from Monday, but new Loose Wet avalanches were easily identified in adjacent zones as temperatures rose and the sun was able to weaken this past weekend’s snow. Looking at weather input, it was certainly sunny and warm in the West South, making us believe that Loose Wet avalanches occurred. How large and widespread the avalanche cycle was on Monday is at the core of our uncertainty moving forward, but we expect a major shedding cycle throughout the week. That said, some clouds and slightly cooler temperatures are forecast for Tuesday, but Loose Wet avalanches will continue to be of concern at all elevations. If you find that a slope produced an avalanche on Monday down to the melt-freeze crust (2/13 interface), it is unlikely that slope will produce a second Loose Wet avalanche during this cycle. Keep in mind that slopes that did avalanche may be connected to higher elevation terrain which has not yet slid, meaning it is not free from danger. Many slopes have not yet reached their tipping point and avalanches Tuesday could be large in isolated areas or could start small before entraining lots of snow, triggering slabs, and traveling far distances as they descend. If you notice signs of these avalanches such as rollerballs, snow shedding from trees and rocks, or new avalanches with fan-shaped debris, then seek out shaded terrain away from sun-exposed slopes above you.

Additionally, with sunshine and warm temperatures this time of year, cornice collapses or glide avalanches are not uncommon. We have some large mature cornices along with fresh cornices from the winds this past weekend. Cornice falls could trigger slabs or start Loose Wet avalanches. Regardless of their age, give these cornices a wide berth by not traveling on or below them and if you see large crevasse like cracks in the snow, avoid slopes below them.

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.

Winds Slabs up to 16” deep were reactive over the weekend and surprised a number of travelers due to fairly poor bonding or unusual loading patterns. East winds like we had during the storm often produce more cross-loading and mid slope loading than we are used to, so there may be wind-loaded features not generally on your radar. A number of the human-triggered slides over the weekend occurred on convex rollovers at middle and upper elevations. Wind Slabs should be stabilizing over the next few days, but for now, you should continue to look for textured snow surfaces or freshly built cornices to help you determine wind-loaded features to avoid. Hand-pits and test slopes can help determine the bond and sensitivity of any potential Wind Slab. If you find reactive pockets of snow or a poor bond, think twice before stepping into consequential terrain.

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.