Introduction into the theory of motions associated with weather systems in the atmosphere. The principal processes that will be discussed are wave motions associated with compressibility, gravity and rotation, motions associated with adjustment to hydrostatic, geostrophic and thermal wind balance and motions associated with hydrodynamic instability. Potential vorticity and frontogenesis are central concepts. Examples of weather systems that will be discussed are seabreeze circulations, thunderstorms, fronts and cyclones.