Figure shows a shallow cumulus in the process of growing into a towering cumulus. The cloud is mostly updraft with weak vertical motions. Downward motions occur only along the edges of the cloud and are associated with turbulence and entrainment. Most of the cloud lies below the freezing level but a part of the cloud penetrates above the freezing level and even above the –10°C level. The –10°C level is noted since it is an important temperature threshold for ice nucleation, to be discussed shortly.