What is the dividing line between cumulus and cumulonimbus clouds? How tall does a cumulus cloud have to be before it is called a cumulonimbus cloud?
In the four major cloud groups, cumulus and cumulonimbus are “clouds with vertical development.” Cumulus clouds are detached, fair-weather clouds with relatively flat bases and dome-shaped tops. They usually don’t have extensive vertical development or produce precipitation. Cumulonimbus clouds are unstable, large, vertical clouds with dense, boiling tops that bring showers, hail, thunder, and lightning. Vertical-development clouds have bases ranging from 1,600 to 20,000 feet. The cumulus-type clouds usually are in the lower range.