Cumulo- means "heap" or "pile" in Latin. Cumulus clouds are often described as "puffy", "cotton-like" or "fluffy" in appearance, and have flat bases. Cumulus clouds, being low-level clouds, are generally less than 1,000 m (3,300 ft) in altitude unless they are the more vertical cumulus congestus form. Cumulus clouds may appear by themselves, in lines, or in clusters. Cumulus clouds are often precursors of other types of cloud, such as cumulonimbus, when influenced by weather

Contrails; short for "condensation trails") or vapor trails are line-shaped clouds sometimes produced by aircraft engine exhaust, typically at aircraft cruise altitudes several miles above the Earth's surface. Contrails are composed primarily of water, in the form of ice crystals. The combination of water vapor in aircraft engine exhaust and the low ambient temperatures that often exists at these high altitudes allows the formation of the trails. Impurities in the jet exhaust

"So much flying about" By Eric Buechel, Watercolor on Paper with Gauche Highlights. 14" x 20" Detail (Home Page)