Electromagnetic wave propagation in a nonuniform troposphere is studied for a cylindrical model of the earth. The refractive index of the troposphere is assumed to vary both with height and range. The formulation is facilitated by the fact that the field within a piecewise (laterally) uniform section can be represented by a discrete sum of modes that are orthogonal in the transverse plane. Using these radial wave functions, mode conversion at a junction between two laterally uniform structures is analyzed for both TE and TM waves.