Avalanche Forecast

Heavy rain will fall on the previously dry layers of snow. This is a perfect combination for wet avalanches. Much of the rain and avalanches will come overnight, but activity will continue through Saturday. 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. While these avalanches are the second problem on the list, they could have serious consequences. Wind slabs could break above you and could be big enough to kill you. 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.

This is a low likelihood, high consequence problem. The chances of triggering are very low, but the resulting avalanche could be unsurvivable. Few backcountry travelers have experience with avalanches of this magnitude. Use caution in the eastern end of the zone (east of Smith Brook) and anywhere with less than 5 feet of snow on the ground. There, the snowpack is similar to what you will find in the East Central forecast zone. You can trigger deep persistent slab avalanches more easily in these areas. 

The best way to reduce the risk of the high consequence of deep persistent slab avalanches 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.

Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage. They commonly develop when Persistent Slabs become more deeply buried over time.

Deep Persistent Slabs avalanches can be destructive and deadly events that can take months to stabilize. You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.

A snowboarder triggered this Deep Persistent Slab near treeline, well down in the path.

Deep, persistent slabs are destructive and deadly events that can take months to stabilize. You can triggered them from well down in the avalanche path, and after dozens of tracks have crossed the slope. Give yourself a wide safety buffer to handle the uncertainty, potentially for the remainder of the season.