An avalanche occurs when a layer of snow loses its grip on a slope and slides downhill. Avalanches kill one to two people, on average, every year in Washington, although many more are involved in avalanche accidents that do not result in fatalities. Most current avalanche victims are participating in recreational activities in the backcountry where there is no avalanche control. Only one-tenth of 1 percent of avalanche fatalities occurs on open runs at ski areas or on highways.
The avalanche season begins in November and continues until early summer for all mountain areas of the state. In the high alpine areas of the Cascades and Olympics, the avalanche season continues year-round.