Standardized Result Lide, David R. Handbook of Chemistry and Physics . National Weather Service Office, Newport North Carolina. The path length of the discharge is normally several kilometers. The cumulonimbus clouds of thunderstorms are the most common producers of lightning, but it is also produced by cumulus, stratus, and other kinds of clouds, including snowstorms, sandstorms, and clouds over erupting volcanoes.
Lightning can also occur in clean air within a few kilometers of a thunderstorm.
More than half of all discharges occur within a cloud. A rare discharge called an up flash, between large storms and the clear air above, may be caused by electrons cascading down from the ionosphere. At any one time about 2,000 thunderstorms may exist worldwide, producing lighting flashing at a total rate of 100 per second. In an average year, about 100 to 200 persons are killed and several hundred injured by lightning in the United States alone, a death rate exceeding deaths cause by hurricanes and tornadoes.