The momentum equations can be written in a form whereby pressure is replaced by a deviation of pressure from a hydrostatic, horizontally homogeneous base state. This pressure perturbation has both hydrostatic and nonhydrostatic parts owing to density deviations from the horizontally homogeneous base state and three-dimensional wind velocity gradients, respectively. The pressure perturbation also can be decomposed into what are referred to as a dynamic pressure perturbation and a buoyancy pressure perturbation. It is shown that dynamic pressure perturbations arise when deformation or vorticity are present in the velocity field. Buoyancy pressure perturbations arise when vertical buoyancy gradients exist.