Avalanche Forecast

Archived

Dec 11th, 2018–Dec 12th, 2018

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Regions

Snoqualmie Pass.

We have received significant snowfall, strong winds, and have a weak snowpack. This is a recipe for avalanches. It is not the time to travel in areas where avalanches can start, nor linger where they can run or stop.

Discussion

Avalanche Summary

We have received observations of natural and human triggered avalanches in the Snoqualmie Pass area. Some of these avalanches are failing on a layer of buried surface hoar and facets. This is an obvious sign that unstable snow is present in the mountains. Observations suggest you are most likely to find these weak layers above 4000 feet where they survived a recent warm-up and rain event.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.