Theoretical and modelling studies of the flow response to an airstream incident upon mesoscale orography have encompassed consideration of a wide range of factors (e.g. the vertical structure of the upstream flow and stratification, frictional and diabatic effects, and nonlinear and rotational effects). Here attention is focussed on the influence of horizontal (sic. lateral) shear of the incident airstream. The nature of the flow response in the parameter space defined by the orography and the strength and scale the flow is examined by conducting a series of idealised experiments with a version of the non-hydrostatic Canadian MC2 model. It is shown that the spatial variation of the Rossby number (- attributable to the shear) can exert a strong influence upon both the overall nature of the flow response (i.e. balanced or unbalanced) and the detailed flow structure within the balanced or unbalanced regimes. For example, depending on the location and the strength of the shear zone, the modification in the transmission properties of the stream can induce significant interference effects of ineria-bouancy waves, and reduce the occurence and alter the location of wave breaking. The results from the simulations are intepreted in terms of extant theoretical concepts.