In other situations, the cumulus may decrease in height and the bases may gradually spread or develop to form areas of altocumulus. These types of clouds do not normally move rapidly. Altocumulus castellanus, particularly those with turrets, develop rapidly with solar heating of the surface. The changing structure often lead to thunderstorm development. In this case the development is mostly noted in vertical structure.
Development also occurs in other regions adjacent to the existing cloud.
Altocumulus can develop in more than one layer. Therefore, the fact that two layers exist mean that development and dissipating processes can create more complex changes. In fact, the movement in slightly different directions and at relatively different speeds changes the appearance of the cloud. Perhaps breaks may coincide briefly allowing sunshine through. Sometimes, lenticular altocumulus occurs below or just ahead of approaching thunderstorms.