Copyright 1991 by Bruce McMillan
These clouds are named because they are puffy ("cumulo") and because they often are dark clouds which cause rainstorms ("nimbus"). Cumulonimbus clouds are different because they cannot be classified as low, middle or high altitude clouds. These are often storm clouds which can be ten or more miles in height, extending through all the levels of altitude. These clouds form when a front of cool air meets a body of hot, moist air. Cumulonimbus clouds can produce rain showers, snow showers, hail, or even thunderstorms.