Avalanche Forecast

Rain will fall on the previously dry layers of snow. This is a perfect combination for wet avalanches. While loose wet avalanches are likely, they are also easy to predict and avoid. They typically break where you impact the snow. Roller balls and pinwheeling snow are good indicators that you may soon see wet avalanches. If you see avalanches, there's a really good chance you can trigger more in similar terrain. Stay off of steep slopes (over 35 degrees, 40 degrees is perfect) where the upper snowpack is wet. Don't linger below these slopes, as avalanches may occur naturally and come down from above. 

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.

Snow and wind will build fresh wind slabs. You can trigger these avalanches at the highest elevations on leeward slopes. Steer around recently drifted features and where the snow is thickly pillowed. At mid elevations moist snow will be adding an extra element to the snowpack structure. Here you may see both wet avalanches and wind drifting.

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.

While it’s now harder to trigger persistent slabs, the grave consequences remain. The best way to reduce the risk of this low likelihood, high consequence avalanche problem is to:

-Limit the amount of time you spend on or near large slopes 35 degrees and steeper.

-Put an extra buffer of terrain between where you travel and where avalanches could start, run, or stop.

-Stay away from features where avalanches are commonly triggered like: rocks, steep roll-overs and convexities, unsupported slopes ending in cliffs or steep drops, and areas of shallow, variable snow.

-When in doubt, avoid avalanche terrain.

Recent avalanches, collapsing, and tests showing cracks spreading through the snow (propagation) are all signs to minimize your exposure to avalanche terrain. If you were in Icicle Creek, Mission Ridge, or near Washington Pass during the avalanche cycle of Dec 18-20th, it was obvious that mountains were falling down. Now, your challenge is; both the chances of triggering and the consequences of these avalanches are less obvious. Incremental snow and wind in the past week stressed the weak layers that lurk in the snowpack, maintaining the possibility of triggering persistent slabs. Due to the uncertain nature of these avalanches, it's best to minimize your exposure to avalanche terrain.

If you dig you'll find the classic strong over weak snow layers of a slab avalanche. A layer of small facets and surface hoar was buried on December 9th and can be found in the lower half of the snowpack on most slopes. At upper elevations a deeper layer of facets can be found close to the ground.

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.