Cumulus mediocris

(Section 2.5.2.9.2)

Below the cloud. The usually horizontal base of Cumulus mediocris is a little darker than the base of Cumulus humilis, and turbulence is often strong.

Within the cloud. This cloud is composed of water droplets (sometimes supercooled). Visibility is variable, and often very poor or even zero. There may be light to moderate icing. Ascending currents may exceed 5 m/s (17 ft/s). Turbulence is fairly severe.

Above the cloud. Viewed from above, these Cumulus clouds show slight or moderate projections or domes, which may vary in size from one cloud to another. White cloud veils (pileus or velum) may be observed over Cumulus mediocris. Cumulus mediocris clouds may occasionally be arranged in rows oriented in the direction of the wind. These “cloud streets” may look like Stratocumulus when viewed from a considerable distance.

Note that Cumulus mediocris includes cumuliform clouds with variable vertical development (pre­-thunderstorm convection sky), which usually have ragged borders and torn tops. They rapidly reach the stage of Cumulonimbus after a short passage through that of Cumulus congestus.