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 may or may not show the cauliflower form characteristic of cumulus clouds. These clouds do not generally produce precipitation, but may further advance into clouds such as cumulus congestus and Cumulonimbus, which do.
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 cloud is thickening, if thinning can lead to calm weather).