Solution of constant values of φ for WKB approximation of a fast wave generated on lower boundary for −1 ≤ x₀ ≤ 1, y₀ = 0, z₀ = 0.2 and its resultant propagation in the xz-plane at various times. Displayed times have been chosen to best illustrate evolution so time between frames is not necessarily uniform. The wavefront consists of crosses from the WKB wave solution, to better illustrate the evolution. The red separatrices in the xz-plane are also shown to provide context.