Clouds Formation

Family D1 clouds have low to middle bases anywhere from near surface to about 10,000 ft (3,000 m) and therefore do not fit very well into the conventional height ranges of low, middle, and high. This group continues the pattern of comprising one cumuliform and one stratiform-category genus. Cumulus usually forms in the low altitude range but bases may rise into the lower part of the middle range during conditions of very low relative humidity. Nimbostratus normally forms from altostratus in the middle altitude range but the base typically subsides into the low range during precipitation.
Family D1 includes:
- Genus Cumulus (Cu): Clouds of free convection with clear-cut flat bases and domed tops. Towering cumulus (cumulus congestus) are usually classified as family D2 clouds of considerable vertical development.
+ Species Cumulus fractus (Cu fra): Cumulus clouds broken up into ragged and changing fragments.