Avalanche Forecast

Strong to extreme winds will blow several 1-2 feet of new, low-density snow far and wide. Any wind-affected snow is likely to be reactive. Wind slabs may be very large and may form at any elevation, may cross-load slopes into the treeline band, and may run full path. The wind slabs will be sitting on faceted (weak) snow above a firm crust (sliding bed surface), which is a prime recipe for very dangerous slab avalanches. Stick to lower angle terrain in dense old-growth trees where safer conditions may be found.

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.

Heavy snowfall will form a deep slab that will produce large natural and human-triggered avalanches. This slab may be reactive within the storm snow or on the new/old snow interface. The last storm snow buried surface hoar or near surface facets near and below treeline or a crust BTL and on sun-affected aspects. Areas that had weak underlying snow are most likely to produce large avalanches. Winds will keep the storm slab problem confined to lower-elevation sheltered terrain. Don’t be lulled into thinking that open slopes are safe at any elevation.

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.