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South Central Avalanche Control

Purpose and goal:

To decrease hazard to motorists from avalanches, and to reduce highway closure time caused by avalanches and avalanche hazard.

An avalanche is a snow slide. A simple explanation is that the snow on a slope will slide (avalanche) when the snow strength can no longer support its own weight.

Active Avalanche Control

Active avalanche control is the intentional triggering of slides. This control work is done to minimize the chance of natural avalanches into traffic. Avalanche control work is done all over the world; by highway departments, ski resorts, railroads, mining operations, utility companies, and other activities threatened by avalanches.

WSDOT does avalanche control to force snow to avalanche while traffic is clear of the hazardous area and snow removal equipment is on hand. This work is most likely to occur during times of heavy snowfall, when traffic is already presented with traction related challenges. To be effective avalanche control must usually be done when the snow is somewhat unstable, or just before the snow will avalanche naturally. This pre-emptive triggering of avalanches produces more frequent and smaller avalanches that will take less total time to clear than larger or natural avalanches.

Thousands of avalanches fall in the mountains of Washington every winter. In a big winter over a hundred avalanches can affect the highway over Snoqualmie Pass. These can be big or small. Even a small avalanche into traffic is a potential for accidents and/or delays. Weather and snow pack conditions are continually monitored throughout the winter months to evaluate avalanche potential.

Map of I90 Snoqualime Pass


Highway safety is our ultimate concern!