Avalanche Forecast

The winds on Saturday formed wind slabs on many open slopes. Areas that received sustained moderate winds, such as Paradise and Chinook Pass, were the most susceptible to wind slab development. At locations such as Crystal and White Pass, the winds were so strong, that the loading pattern was more erratic. Winds were generally out of the East, which can create unusual loading patterns where wind slabs form on slopes normally scoured by prevailing winds. Keep your eyes open for signs of wind transported snow. Do you see fresh cornices, drifted snow, or uneven snow surfaces? If you answer, “yes,” wind slabs are likely nearby. Avoid wind loaded slopes greater than 35 degrees.

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.

With so much new snow, especially around the volcanoes, we’re concerned about the triggering slab avalanches within the recent snow. This may take settlement of the new snow either from the sun or simply time. You’ll need to check the snow as you travel for strong over weak structure. Small slope tests, and simple hand pits can help you look for storm slabs as you travel. Does the snow change by aspect? How does it change throughout the day? Is the sun causing a slab to develop on sunny slopes? If you find stronger storm snow over weaker snow, avoid slopes greater than 35 degrees.

In areas that received less snow, or where the snow has not settled, you may trigger loose dry avalanches. Even though these avalanches are easier to predict, they aren’t to be trifled with. They can be dangerous if you are traveling in high consequence terrain, such as near gullies or cliffs.

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.