Avalanche Forecast

Ridgetop winds have averaged 20-40 mph and gusting to 60 mph over the past two days. 3 feet or more of storm snow combined with these strong winds are building deep slab layers in exposed terrain, with large hard slabs forming above treeline. Any wind-affected snow is likely to be very sensitive to human triggering. Most wind slabs overlie faceted (weak) snow above a firm crust (sliding bed surface), which is a dangerous recipe for slab avalanches. Avoid avalanche terrain and stick to low angle sheltered terrain well away from open slopes above.

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.

Continued snowfall overnight will continue to build unstable slabs that may produce large natural or human-triggered avalanches. A very weak underlying snow structure exists in most areas, consisting of weak snow that may be poorly bonded to a hard crust, especially on any southerly facing terrain. Winds will keep the storm slab problem confined mostly to sheltered terrain. It will be best to avoid steep slopes greater than 35 degrees and seek out wind sheltered terrain Wednesday.

Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.

You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.

Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.