Aside from the basic cloud types (Cirrus, Cumulus and Stratus), there are also cloud sub-categories. A cloud that produces rain has the term Nimbus attached to it, as in cumulonimbus, or nimbostratus, depending on the form and height of the rainmaker. The prefix Alto is added to cloud names that appear at roughly the middle layers of the atmosphere. For example, a stratus cloud that appears well above the surface would be called an altostratus cloud.
---D.M.
