Cumulus mediocris

Cumulus mediocris cloud
Cumulus mediocris clouds above Auckland with streaks of light precipitation visible in the distance.
Abbreviation	Cu
Symbol
Genus	Cumulus (heaped)
Species	mediocris (moderate)
Altitude	500-3000 m (1,500-10,000 ft)
Appearance	Medium to large cumulus clouds
Precipitation cloud?	Uncommon, but it can develop into a cumulus congestus which is a common precipitation cloud

Cumulus mediocris is a low to middle level cloud with some vertical extent (Family D1) of the genus cumulus, larger in vertical development than cumulus humilis. It also may exhibit small protuberances from the top. It may or may not show the cauliflower form characteristic of cumulus clouds. These clouds don't generally produce precipitation of more than very light intensity, but may further advance into clouds such as cumulus congestus and Cumulonimbus, which do.

Species Cumulus mediocris (Cu med) achieves moderate vertical development, has medium-grey shading underneath. This larger species is also classified as a low cloud by some authorities and is coded C_L2 on the synop report.

These clouds are common in the advance of a cold front or in unstable atmospheric conditions such as an area of low pressure. They can grow into larger clouds (Cumulus Congestus) which could bring rain, winds and in worse cases, thunder and lightning. If these clouds are present in the morning or early afternoon they show a significant instability in the atmosphere likely leading to storms later in the day (if the cloud is thickening, if thinning can lead to calm weather).

These clouds occur when there is more rising air than the Cumulus Humilis. Like any cumulus cloud, this cloud requires convection before developing. This occurs when pockets of air around them become warmer and begin to rise. As the air rises, it condenses forming a cumulus humilis cloud as it continues to rise, a cumulus mediocris.