An avalanche is a mass of snow that loses its grip and slides down a slope. Avalanches occur where snow can collect on a steep slope. There are two types of avalanches, loose and slab, and two types of slab avalanches, dry and wet. Although the most dangerous avalanche is the slab avalanche, loose slides can and do produce injury and death.
In Idaho, they are found in the mountainous portions of the state. They can occur rapidly, can be difficult to predict with certainty, and are sometimes initiated by their victims. The Colorado Avalanche Information Center reported sixty-eight fatalities in Idaho from 1950 through 2006. Snowmobiling is the leading cause of avalanche fatalities in Idaho. Avalanches often occur near transportation routes, interrupting travel and threatening those passing by.
Four avalanche centers operated by the US Forest Service and supported by private non-profit organizations provide hazard monitoring and forecasting, broadcasting of public information and avalanche safety education. These centers collect data through remote instruments, field work, public observations and National Weather Service information products to generate hazard forecasts. Avalanche and mountain weather advisories based on these observations are made available through phone or web services. The centers also provide education for recreational users of the backcountry and avalanche awareness for the general public. When avalanche hazards are high to extreme, the National Weather Service offices in Boise and Pocatello issue avalanche reports by through Snow Avalanche Bulletins.