Avalanche Forecast

Avalanches may begin on east and southeasterly aspects early in the day and continue onto southwest aspects by afternoon. You may see these avalanches start to occur at higher elevations and even onto northwest aspects as the warm weather continues. Look for signs of loose wet instability such as wet, heavy surface snow, rollerballs, and fan-shaped avalanches. If you notice these clues, avoid going underneath steep slopes where loose wet slides may run naturally.

The cloud cover has been ongoing and challenging to predict this week. The loose wet avalanche cycle has been prolonged and slow to run its course. As you travel through the mountains, take note of how much the sun is affecting the snow surface and creating avalanches.

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.

The recent storm snow landed on a variety of surfaces from surface facets and surface hoar on shaded aspects to melt-freeze crusts on southerly aspects. Winds built slabs on exposed open slopes. Winds transported both the recent storm snow, and snow that was previously on the surface. Even locations that didn't receive much new snow may have recently formed wind slabs. The snow may fracture quite wide on shaded aspects where the recently buried layer is weak and faceted. Any avalanches on the old surface may step down a foot or so to layers from early March. Check for thick, cohesive layer of snow sitting over a weaker snow layer. If you see obvious clues to instability such as shooting cracks and wind loaded texture, it's a good bet to stay off of steep wind loaded slopes. 

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.

At lower elevations, where the snowpack is shallow, a poor structure can be found with facets underneath a crust from early February This shallow snowpack is weak, especially on shaded aspects. In the foothills, facets can be found near the ground beneath February's storm snow. These deeper slabs are most concerning on isolated, shaded slopes where stronger snow may rest over facets. At upper elevations, these layers are generally not a concern anymore. 

If you find yourself in an area that appears to have a shallow snowpack, stick to well supported slopes and avoid steep convex rolls. Travel one at a time from well defined safe zones when moving through steeper terrain. If you find signs of instability such as cracking and collapsing, avoid steep slopes nearby. 

Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slabs.

The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices. They can be triggered by light loads and weeks after the last storm. The slabs often propagate in surprising and unpredictable ways. This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.

This Persistent Slab was triggered remotely, failed on a layer of faceted snow in the middle of the snowpack, and crossed several terrain features.

Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.